Anna Frebel: Origin and Evolution of the Universe, Galaxies, and Stars

00:00:00.000 | I would run outside and just lay on the ground under the southern Milky Way, beautiful right

00:00:07.380 | up there.

00:00:09.140 | And I would just lay there like the snow angel and just kind of let my thoughts sort of pass

00:00:14.300 | through my brain.

00:00:15.300 | And this is when I personally have the feeling that I'm a part of it.

00:00:19.380 | I belong here, rather than feeling kind of small.

00:00:22.620 | Yes, I'm small, but there are many other small things, and lots of small things make one

00:00:26.960 | big whole.

00:00:27.960 | The following is a conversation with Anna Frabel, an astrophysicist at MIT, studying

00:00:35.800 | the oldest stars in the Milky Way galaxy in order to understand the chemical and physical

00:00:40.840 | conditions of the early universe, and how from that, our galaxy formed and evolved to

00:00:47.840 | what it is today, the place we humans call home.

00:00:52.440 | This is the Lex Friedman Podcast.

00:00:53.960 | To support it, please check out our sponsors in the description, and now, dear friends,

00:00:59.600 | here's Anna Frabel.

00:01:02.440 | Let's go back to the early days.

00:01:04.040 | What did the formation of the Milky Way galaxy look like?

00:01:07.960 | Or maybe we want to start even before that.

00:01:10.080 | What did the formation of the universe look like?

00:01:13.080 | Well, we scientists believe there was the Big Bang, some big beginning.

00:01:19.200 | But what is important for my work, and I think that's what we're going to talk about, is

00:01:23.440 | what kind of elements were present at that time.

00:01:27.520 | So the Big Bang left a universe behind that was made of just hydrogen and helium, and

00:01:32.800 | tiny little sprinkles of lithium.

00:01:36.200 | And that was pretty much it.

00:01:38.980 | As it turns out, it's actually quite hard to make stars or any structure from that.

00:01:44.840 | That's fairly hot gas.

00:01:47.960 | And so the very first stars that formed prior to any galaxies were very massive stars, big

00:01:55.400 | stars, 100 times the mass of the Sun, and they were made from just hydrogen and helium.

00:02:01.240 | So big stars explode pretty fast after a few million years only.

00:02:05.760 | That's very short on cosmic time scales.

00:02:08.840 | And in their explosions, they provided the first heavier elements to the universe because

00:02:14.400 | in their cores, all stars fuse lighter elements like hydrogen and helium into heavier ones.

00:02:21.440 | And then that goes all the way up to iron, and then all that material gets ejected in

00:02:25.840 | these massive supernova explosions.

00:02:28.960 | And that marked a really, really important transition in the universe because after that

00:02:36.120 | first explosion, it was no longer chemically pristine.

00:02:42.080 | And that set the stage for everything else to happen, including us here talking today.

00:02:47.000 | - So what do you mean by pristine?

00:02:48.960 | So there's a whole complex soup of elements now as opposed to just hydrogen, helium, and

00:02:56.400 | a little bit of lithium.

00:02:57.840 | - Yeah, so after the Big Bang, just hydrogen and helium.

00:03:01.320 | We don't really need to talk too much about lithium because the amount was so small.

00:03:06.800 | And after these very first stars formed and exploded, heavier elements like carbon, oxygen,

00:03:14.960 | magnesium, iron, all of that stuff was suddenly present in the gas clouds.

00:03:22.280 | Tiny amounts only, very tiny amounts.

00:03:25.280 | But that actually helped, especially the carbon and the oxygen, to make the gas cool.

00:03:31.720 | These atoms are more complicated than hydrogen.

00:03:34.840 | It's just a proton, and so it has cooling properties, can send out photons outside of

00:03:39.000 | the gas cloud so the gas can cool.

00:03:41.440 | And when you have gas that gets colder and colder, you can make smaller and smaller stars.

00:03:45.600 | So you can fragment it and clump it and turn it into stars like the Sun.

00:03:50.560 | And the cool thing about that is that when you have small stars like the Sun, they have

00:03:55.200 | a really long lifetime.

00:03:57.380 | So those first low-mass stars that formed back then are still observable today.

00:04:02.700 | That is actually what I do.

00:04:03.880 | I try to find these early survivors because they tell us what the gas looked like back

00:04:09.960 | then.

00:04:10.960 | They have preserved that composition of these early gas clouds, the chemical compositions,

00:04:16.800 | until today.

00:04:18.200 | So I don't need to look very far into the universe to study all the beginnings.

00:04:24.740 | I can just chemically analyze the oldest stars, and it's like unpacking everything that happened

00:04:32.400 | back then.

00:04:33.400 | It's exciting.

00:04:34.400 | - So to just reiterate, so in the very early days in the first few million years, there

00:04:39.960 | was giant stars that's mostly hydrogen and helium, and then they exploded in these supernova

00:04:44.760 | explosions, and then they made these clumps.

00:04:47.960 | - Yeah, so the first stars--

00:04:50.120 | - Non-pristine.

00:04:51.120 | (laughing)

00:04:52.120 | Non-pristine clumps.

00:04:53.120 | - Yeah, pretty much.

00:04:54.120 | - Fun.

00:04:55.120 | - So it took a few hundred million years for the first stars to emerge, and then they exploded

00:04:59.000 | after a few million years.

00:05:00.960 | Kaboom.

00:05:02.000 | And then it's like, I always consider the universe like a nice soup, and then these

00:05:09.080 | first supernova explosions kind of provided the salt, just a little sprinkle of heavier

00:05:14.440 | elements, and that made it really tasty.

00:05:17.600 | Just changed it completely, right?

00:05:20.000 | And that changed the physics of the gas, so that meant that these gas clouds that were

00:05:26.400 | surrounding the former first stars, they could now cool down and clump and form the

00:05:32.240 | next generation of stars that now included also little stars.

00:05:38.000 | And as I just mentioned, the small stars have these really long lifetimes.

00:05:42.920 | The Sun has a lifetime of 10 billion years.

00:05:45.920 | Any star that is even less massive will have an even longer lifetime.

00:05:50.480 | So that gives us a chance to still observe some of the stars that formed back then.

00:05:55.600 | So we are testing the conditions, the chemical and physical conditions of the early universe

00:06:00.480 | even before the galaxy formed.

00:06:03.200 | - So what's the timeline that we're talking about?

00:06:05.240 | What is the age of the universe, and what is the earliest time we got those salty, delicious

00:06:09.640 | soup, clump soups with heavier elements?

00:06:13.800 | - Well the universe is 13.8 billion years old.

00:06:16.200 | - Allegedly, yeah.

00:06:17.200 | Is it?

00:06:18.200 | - Yes.

00:06:19.200 | - Okay, 13.8, sorry.

00:06:20.200 | - Well, you know, when I was in high school, the universe was 20 billion years old.

00:06:24.120 | - Oh yeah?

00:06:25.120 | - So the estimate-- - Things have changed.

00:06:26.120 | - Do you think that estimate will evolve in interesting ways or no?

00:06:29.240 | Is it pretty stable at this point?

00:06:30.240 | - I think we have mostly converged, yes.

00:06:32.840 | Because the techniques are very different now, much more precise.

00:06:36.240 | The whole business of precision cosmology by mapping out the cosmic microwave background,

00:06:41.200 | you know, that's a marvelous feat.

00:06:45.720 | Maybe the digits will still move around a little bit, but that's all right.

00:06:49.800 | - Plus the gravitational waves and all that.

00:06:51.880 | So all the different sources of data, kind of mapping out this detailed picture of the

00:06:56.640 | early universe.

00:06:57.640 | - Totally.

00:06:58.640 | And so we think the earliest little stars formed, I don't know, maybe half a billion

00:07:03.720 | years after the Big Bang, right?

00:07:05.600 | Again a few hundred million years for the first stars to emerge, and then it took some

00:07:10.000 | time.

00:07:11.000 | So give or take half a billion years.

00:07:14.600 | And that was the time when sort of the very first proto-galaxies formed, early stellar

00:07:21.400 | structures, stellar systems, from which the Mickey eventually formed, right?

00:07:26.720 | So the Mickey was probably a bigger, slightly bigger one.

00:07:31.400 | And we know today that galaxies grow hierarchically, which means they eat their smaller neighbors.

00:07:37.080 | So if you're the bigger one and have a few friends around, you're just gonna eat them,

00:07:44.360 | absorb them, and then you grow bigger.

00:07:47.120 | And so all these little early stars kind of came into the Mickey way through that kind

00:07:53.200 | of process, and that's why we find them in the outer parts of the galaxy today, because

00:07:59.160 | they're just kind of left there since.

00:08:02.700 | - So the old stuff is on the outskirts of the galaxy, and the new stuff is closer to

00:08:06.640 | the middle?

00:08:07.640 | - Broadly speaking, yes.

00:08:08.640 | - So that's where you would look for it.

00:08:10.960 | So maybe just to step back, what is a galaxy, what is a proto-galaxy?

00:08:15.280 | - I love that question.

00:08:16.420 | So the galaxy is a huge assembly of stars.

00:08:23.560 | The Mickey Way contains something like 200 to 400 billion stars, and most of the material

00:08:30.320 | and the stars are in the disk.

00:08:32.680 | And when we look at the night sky, what we see as the Mickey Way band on the sky, that

00:08:39.680 | is actually the next inner spiral arm, because we actually live in a spiral disk galaxy,

00:08:47.520 | so the Mickey Way is a spiral disk galaxy.

00:08:51.760 | And we're looking, actually it depends a little bit in the northern hemisphere, we're looking

00:08:56.740 | out of the galaxy, so we're seeing the next outer spiral arm.

00:09:03.040 | And as you can imagine, there's only dark space behind that, so we don't see it all

00:09:08.360 | that nice on the sky, but if you travel to the southern hemisphere, let's say South America,

00:09:14.800 | you see the Mickey Way and it looks so different on the sky because that's the next inner spiral

00:09:19.760 | arm, and that's backlit by the galactic center.

00:09:23.640 | The galactic center is a very big, puffy region of gas, there's a lot of star formation, the

00:09:32.000 | galactic party is happening there, so it's very bright, and it makes for this very beautiful

00:09:37.160 | Mickey Way on the night sky that we see.

00:09:39.240 | So actually, if you ever get the chance to experience that, I encourage you to almost

00:09:45.120 | like close your eyes while seeing this and imagining that you're sitting in this kind

00:09:49.600 | of disk, in this pancake, and you're just kind of looking right into it, and you can

00:09:54.960 | really feel that we're in this 2D disk, and then you can imagine that there's a top and

00:10:00.640 | a bottom, and that we're really part of the galaxy, you can really experience that.

00:10:06.040 | We're not just lost in space somewhere, but we're really a part of it, and knowing a little

00:10:11.520 | bit about the structure of the Mickey Way really helps.

00:10:13.840 | - Do you feel small when you think about that?

00:10:17.080 | When you look on the spiral on the inside of the Mickey Way, and then you look out to

00:10:21.320 | the outside, how are we supposed to feel?

00:10:25.200 | - I don't know, I don't feel small necessarily, I feel in awe, and I feel I'm a part of it,

00:10:32.640 | because I can really feel that I'm a part of it.

00:10:36.440 | I think for many people, they think like, "Oh, there's just the planet, and then there's

00:10:40.600 | nothing."

00:10:42.600 | And that's almost a little bit sad, but that's really not the case, right?

00:10:48.040 | Because there's so much more, and I really like to imagine, wow, I'm sitting in this

00:10:52.720 | big galactic merry-go-round, and we're going around the center, and I can see the center

00:10:57.880 | above me, right, and I can almost feel like we're going there.

00:11:03.200 | Of course, we can't really feel that, but the sun does circle the galactic center.

00:11:09.480 | - But there's a kind of sadness to looking pictures of a nice vacation place.

00:11:14.840 | All we get is that light, an old light.

00:11:19.760 | Do you feel sad that we don't get to travel, or you and I will not get to travel there,

00:11:25.520 | and maybe humans will never get to travel there?

00:11:27.760 | - Yeah, I always wanted to travel into space and see the Earth and other things from up

00:11:32.040 | there.

00:11:33.040 | There's certainly that, but I don't know.

00:11:37.760 | It's also okay to just be at our vantage point and see it from here.

00:11:44.000 | - With the sensors, with the telescopes that we have, and explore the possibility.

00:11:47.880 | There is a kind of wonder to the mystery of it all, what's out there, what interesting

00:11:52.560 | things that we can't possibly imagine.

00:11:54.760 | There could be all kinds of life forms, bacteria, all this kind of stuff.

00:11:58.520 | I tend to believe that, it depends on the day, I tend to believe there's just a lot

00:12:04.560 | of very primitive organisms just spread out throughout, and they built their little things

00:12:09.400 | like bacteria-type organisms, just to think what kind of worlds there are, 'cause they're

00:12:15.480 | probably really creative living organisms.

00:12:17.720 | 'Cause the conditions, I guess the question I'm wondering to myself when I look out there

00:12:22.800 | to the stars, how different are the conditions on the different planets that orbit those

00:12:27.160 | stars?

00:12:28.160 | - It will definitely be very different.

00:12:29.760 | I mean, the variety out there is huge.

00:12:33.700 | We know now that I think it's about every other star has at least one planet.

00:12:41.840 | I already mentioned the number of stars in the galaxy.

00:12:44.400 | I mean, it's a huge number of planets out there, so who knows what that looks like.

00:12:52.200 | All we know is that there is a lot of variety.

00:12:56.040 | We don't quite yet understand what drives that, what governs that, why that is the case,

00:13:02.420 | why is it not all one size fits all?

00:13:04.360 | - You mean the dynamics of planet formation, like exoplanet formation, or star formation,

00:13:09.840 | the whole--

00:13:10.840 | - All of it, all of it.

00:13:12.560 | Star formation remains a much-researched topic.

00:13:16.520 | We definitely know that it works, because all the stars are there.

00:13:21.620 | Same for the planets.

00:13:23.200 | But the details are so varied per gas cloud, right?

00:13:29.080 | It's very hard to come up with very detailed prescriptions.

00:13:34.200 | Broadly we have figured it out.

00:13:35.360 | You need a gas cloud, you need to cool it, something clumps and fragments, and somehow

00:13:40.920 | it makes a star with planets or without.

00:13:44.320 | - But the dynamics of the clumping process is not fully understood.

00:13:47.160 | - No, no.

00:13:48.700 | The local conditions are so varied, right?

00:13:51.980 | I mean, it's the same with, all people look like people, but individually we look very

00:13:56.900 | different.

00:13:57.900 | - So even the subtle diversity of the formation process creates all kinds of fun differences.

00:14:02.460 | - Yes, so we just don't know how this turned out in an individual case.

00:14:07.580 | And it's kind of hard to figure it all out and to take a look, certainly with planets,

00:14:14.420 | the chance to ever actually take a picture of a planet is minuscule, because they don't

00:14:21.020 | shine, so they're really dark.

00:14:23.260 | So I'd say there's a lot of possibility out there, but we have to be a little bit more

00:14:29.860 | patient before we--

00:14:32.100 | - Come up with technologies where patience becomes less necessary by extending our lifetimes

00:14:38.380 | or increasing the speed of space travel, all that kind of stuff.

00:14:42.940 | Humans are pretty intelligent.

00:14:44.420 | - Sometimes, yeah.

00:14:45.420 | - For the most part, I hope, on the optimistic days.

00:14:52.580 | Well maybe just to linger on what a galaxy is, what should we know about our understanding

00:15:00.420 | of black holes in the formation?

00:15:02.540 | Is that an important thing to understand in the formation of a galaxy?

00:15:07.060 | So all the orbiting, all the spiraling that's going on, how important is that to understand?

00:15:11.660 | - All of the above.

00:15:13.540 | That's what makes astronomy really hard, but also really interesting, right?

00:15:17.460 | No day is like another because we always find something new.

00:15:21.060 | I want to come back to the idea of the proto-galaxy because it actually matches or relates to

00:15:26.900 | the black hole formation.

00:15:28.500 | So most large, well pretty much all large galaxies have a supermassive black hole in

00:15:33.580 | the center, and we don't actually know, we don't really know where they come from.

00:15:38.660 | Again, we know that they are there, but how do we get there?

00:15:43.020 | So we go back to the early universe, right?

00:15:46.220 | We had a little galaxy that just sort of, I don't know, had some small number of stars.

00:15:54.220 | It was the first gravitationally bound structure that was held together by dark matter because

00:16:00.220 | dark matter actually kind of structured up first before the luminous matter could because

00:16:06.780 | that's what dark matter kind of does.

00:16:08.740 | And it started to hold gas and then stars sort of together in these first very shallow,

00:16:16.820 | what we call potential wells, so these gravitationally bound systems.

00:16:21.100 | And then the Milky Way grew from absorbing neighboring smaller, even smaller systems.

00:16:27.260 | And somewhere in that process, there must have been a seed for one of these supermassive

00:16:34.980 | black holes, and I'm not actually sure that it's clear right now kind of what was there

00:16:39.980 | first, the supermassive black hole or the galaxy.

00:16:45.540 | So lots of people are trying to study that, and of course the black hole wasn't as massive

00:16:49.700 | back then as it is these days.

00:16:52.780 | But it's a big area of research, and the new James Webb, the JWT, the telescope, the infrared

00:17:00.980 | telescope in space is working on, many people are working on that to figure out exactly

00:17:09.380 | what happened.

00:17:10.380 | And there are some surprising results that we really don't understand right now.

00:17:15.060 | - So to solve the chicken or the egg problem of do you need a supermassive black hole to

00:17:20.540 | form a galaxy, or does the galaxy naturally create the supermassive black hole?

00:17:24.460 | - Yeah, yeah.

00:17:25.460 | I mean, I think to some degree we can answer that because there are lots of little dwarf

00:17:29.700 | galaxies out there.

00:17:31.940 | The Milky Way remains surrounded by many dozens of small dwarf galaxies.

00:17:37.820 | I have studied a bunch of them, and to the extent that we can tell, they do not contain

00:17:42.900 | black holes.

00:17:44.580 | So there certainly were gravitationally bound structures, so either you can call them proto-galaxies

00:17:50.100 | or dwarf galaxies or first galaxies, they were definitely there.

00:17:54.700 | But there must have been bigger things like the proto-Milky Way where something was different,

00:18:00.580 | right?

00:18:01.580 | What made them more massive so that they would gravitationally attract these smaller systems

00:18:06.940 | to integrate them.

00:18:09.540 | So we'll have to see.

00:18:11.180 | - How do we look into that, into the dynamics of the formation, the evolution of the proto-galaxies?

00:18:17.980 | Is it possible?

00:18:18.980 | Do they shine?

00:18:19.980 | I mean, what are the set of data that we can possibly look at?

00:18:24.180 | So we got gravitational waves, which is really insane that we can even detect those.

00:18:31.140 | There's light.

00:18:33.060 | What else can we--

00:18:34.060 | - So that would fall into the category of observational cosmology, and the JWT is the

00:18:40.540 | prime telescope right now, and it promises big, big steps forward.

00:18:47.220 | This is in its early days because it's only been online like a year or so.

00:18:53.220 | And that collects the infrared light from the farthest, like literally proto-galaxies,

00:19:01.260 | earliest galaxies.

00:19:02.820 | That light has traveled some 13 billion years to us, and they're observing these faint little

00:19:07.780 | blobs.

00:19:11.060 | And folks are trying to, again, study the onset of these early supermassive black holes,

00:19:17.460 | how they shape galaxies.

00:19:18.940 | So they're seeing that they were there, surrounded by already bigger galaxies.

00:19:24.900 | Ideally, I'd like for my colleagues to push a little bit further.

00:19:28.940 | Hopefully that will eventually happen.

00:19:30.620 | - In terms of looking towards older and older ones.

00:19:33.460 | - Yeah, yeah, more and more sort of primitive in terms of the structure.

00:19:37.620 | But of course, as you can imagine, if you make your system smaller and smaller, it becomes

00:19:42.300 | dimmer and dimmer, and it's further and further away.

00:19:45.700 | So we're reaching the end of the line from a technical perspective pretty quickly.

00:19:49.900 | - But dimmer and dimmer means older and older.

00:19:52.940 | - Yes, in a sense, because it all started really small.

00:19:57.420 | - Because it's smaller and smaller, which correlates to older and older.

00:20:01.020 | - In that phase of the universe, it would, otherwise it doesn't.

00:20:05.860 | - Just to take a small attention about black holes, because you do quite a bit of observational

00:20:12.680 | cosmology and maybe experimental astrophysics.

00:20:19.940 | What's the difference to you between theoretical physics and experimental?

00:20:23.620 | So there's a lot of really interesting explorations about paradoxes around black holes and all

00:20:29.100 | this kind of stuff, about black holes destroying information.

00:20:34.020 | Do those worlds intermix to you, especially when you step away from your work and kind

00:20:38.500 | of think about the mystery of it all?

00:20:41.180 | - Well, at first glance, there isn't actually much crosstalk.

00:20:46.340 | Personally, I mostly observe stars, so I don't usually actually think too much about black

00:20:53.140 | holes.

00:20:54.140 | - And stars is a fundamentally kind of chemical, physical phenomena that doesn't...

00:20:58.060 | - That's right.

00:20:59.060 | The physics is kind of different.

00:21:00.060 | It's not extreme.

00:21:01.060 | I mean, you know, you could consider nuclear fusion sort of be perhaps extreme.

00:21:06.220 | You need to tunnel.

00:21:07.220 | There's some interesting physics there.

00:21:10.220 | - Yeah, yeah.

00:21:11.220 | - But it's just a different flavor.

00:21:13.900 | I don't do these kinds of calculations myself either.

00:21:19.700 | I very much like to talk with my theory colleagues about these things, though, because I find

00:21:23.940 | there's always an interesting intersection.

00:21:26.820 | And often, it's just...

00:21:29.860 | I've written a number of papers with colleagues who do simulations about galaxies, and so

00:21:37.500 | they're not quite as far removed as, let's say, the black hole pen and paper folks.

00:21:42.700 | But even in those cases, we had the same interests and the same topics, but it was almost like

00:21:48.340 | we're speaking two different languages.

00:21:50.060 | And we weren't even that far removed, you know, both astronomers and all.

00:21:54.980 | And it was really interesting just to take the time and really try to talk to each other.

00:22:02.500 | And it's amazing how hard that is.

00:22:08.540 | You know, even amongst scientists, we already have trouble talking to each other.

00:22:12.420 | Imagine how hard it is to talk to non-scientists and other people to try, you know, to...

00:22:18.860 | We're all interested in the same things as humans at the end of the day, right?

00:22:22.140 | But everyone has sort of a different angle about it and different questions and way of

00:22:27.060 | formulating things, and sometimes it really takes a while to converge and to get, you

00:22:33.300 | know, to the common ground.

00:22:34.860 | But if you take the time, it's so interesting to participate in that process.

00:22:39.180 | And it feels so good in the end to say like, "Yes, we tackled this together," right?

00:22:43.140 | We overcame our differences, not so much in opinion, but just in expressing ourselves

00:22:48.540 | about this and how we go about solving a problem.

00:22:51.900 | And these were some of my most successful papers, and I certainly enjoyed them the most.

00:22:56.580 | - It could also lead to big discoveries.

00:22:58.380 | I mean, there's a...

00:22:59.380 | I think you put it really well in saying that we're all kind of studying the same kind of

00:23:04.020 | mysteries and problems.

00:23:05.260 | I mean, I see this in the space of artificial intelligence.

00:23:08.580 | You have a community, maybe it seems very far away, artificial intelligence and neuroscience.

00:23:14.180 | You know, you would think that they're studying very different things, but one is trying to

00:23:17.380 | engineer intelligence and in so doing, try to understand intelligence.

00:23:22.380 | And the other is trying to understand intelligence and cognition in the human mind.

00:23:28.380 | And they're just doing it from a different set of data, a different set of backgrounds,

00:23:31.940 | and the researchers that do that kind of work.

00:23:33.900 | And probably the same is true in observational cosmology and simulation.

00:23:41.500 | So it's like a fundamentally different approach to understanding the universe.

00:23:47.540 | Let me use, for simulation, let me use the things I know to create a bunch of parameters

00:23:53.460 | and create some...

00:23:55.180 | Just play with it.

00:23:56.420 | Play with the universe.

00:23:58.060 | Play God.

00:23:59.820 | Create a bunch of universes and see in a way that matches experimental data.

00:24:05.060 | It's a fun...

00:24:06.060 | It's like playing Sims, but at the cosmic level.

00:24:09.140 | - Yes, yes.

00:24:10.140 | - And then probably the set of terminology used there is very different.

00:24:13.500 | And maybe you're allowed to break the rules a little bit more.

00:24:16.340 | Let's have, you know, yeah, it's like the Drake equation.

00:24:19.060 | Yeah, you don't really know.

00:24:20.420 | You kind of come up with a bunch of values here and there and just see how it evolves.

00:24:24.700 | And from that, kind of intuit the different possibilities, the dynamics of the evolution

00:24:29.340 | of a galaxy, for example.

00:24:31.180 | Yeah, but it's cool to play between those two.

00:24:34.340 | Because it seems like we understand so little about our cosmos.

00:24:38.620 | So it's good to play.

00:24:39.780 | - Yes, it's like a big sandbox, right?

00:24:42.340 | And everyone kind of has their little corner and they do things, but we're all in the same

00:24:46.780 | sandbox together at the end of the day.

00:24:49.300 | - But in that sandbox does have super powerful and super expensive telescopes.

00:24:54.300 | That everybody's also...

00:24:56.180 | All the children are fighting for the resources to make sure they get to ask the right questions

00:25:00.740 | using that big cool tool.

00:25:02.940 | Well, can we actually step back on the big field of stellar archeology?

00:25:09.980 | What is this process?

00:25:10.980 | Can you just speak to it again?

00:25:11.980 | I know you've been speaking to it, but what is this process of archeology in the cosmos?

00:25:16.780 | - Yeah, it's really fascinating.

00:25:19.420 | So I mentioned the lesser the mass of the star, the longer it lives.

00:25:27.660 | And again, for reference, for the next dinner party, the sun's lifetime is 10 billion years.

00:25:33.380 | So if you have a star that's 0.6 or 0.8 solar masses, then its lifetime is going to be 15

00:25:40.940 | to 20 billion years.

00:25:42.940 | And that's an important range for our conversation because again, if you assume that such a small

00:25:48.340 | star formed soon after the Big Bang, then it is still observable today.

00:25:53.280 | You mentioned old light before.

00:25:55.860 | That light is like a few thousand years old, but compared to the age of these stars is

00:26:00.460 | nothing.

00:26:02.100 | So to me, that's young.

00:26:05.980 | Because straight from our galaxy, these stars are not far away.

00:26:10.780 | They're in our galaxy in the outskirts.

00:26:14.100 | They probably did not form in the galaxy because again, hierarchical assembly of a Milky Way

00:26:22.300 | meant...

00:26:23.300 | - They were eaten.

00:26:24.300 | - Exactly.

00:26:25.300 | They formed in a little other galaxy in the vicinity.

00:26:27.580 | And at some point, the Milky Way ate that, which means it absorbed all the stars, including

00:26:32.220 | these little old stars that are now in the outskirts of the Milky Way that I used to

00:26:35.860 | point my telescope to.

00:26:38.180 | So what can we learn from these stars?

00:26:41.620 | Why should we study them?

00:26:42.740 | Now these little stars are really, really efficient with their energy consumption.

00:26:48.660 | They're still burning, for the experts, just burning hydrogen to helium in their cores,

00:26:53.260 | and they have done so for the past 12, 13 billion years, however old they are.

00:26:58.780 | And they're going to keep doing that for another few billion years, same as the Sun.

00:27:02.540 | The Sun also just does hydrogen to helium burning and will continue that for a while.

00:27:07.820 | Which means the outer parts of the star, well, pretty much actually most of the star, that

00:27:15.540 | gas doesn't talk to the core.

00:27:19.180 | So whatever composition that star has, you know, in its outer layers, is exactly the

00:27:27.460 | same as the gas composition from which the star formed.

00:27:32.220 | Which means it has perfectly preserved that information from way back then all the way

00:27:38.780 | to today and going forward.

00:27:42.100 | So I'm a stellar archaeologist because I don't dig in the dirt to find remnants of past civilizations

00:27:49.340 | and whatnot.

00:27:51.700 | I dig for the old stars in the sky because they have preserved that information from

00:27:57.900 | those first billion years in their outer stellar atmosphere, which is what I'm observing with

00:28:05.860 | telescopes.

00:28:06.860 | So I'm getting the best look at the chemical composition early on that you could possibly

00:28:12.860 | wish for.

00:28:13.860 | - What kind of age are we talking about here?

00:28:15.860 | Are we talking about something that's close to that, you know, like a 13 billion, 12,

00:28:22.100 | 13 billion age range?

00:28:23.980 | - That's what we think.

00:28:26.420 | Now there's a small caveat here.

00:28:28.300 | We can not accurately date these stars, but we use a trick to say, "Oh, these stars must

00:28:35.820 | have formed as some of the earliest generations of stars."

00:28:39.700 | Because we need to talk about the chemical evolution of the universe and the Milky Way

00:28:43.140 | for a second.

00:28:44.540 | So I already mentioned the pristineness of the universe after the Big Bang, right?

00:28:51.580 | Just hydrogen and helium.

00:28:53.100 | Then the first stars formed, they produced a sprinkle of heavier elements up to iron.

00:28:59.180 | Then the next generation of stars formed.

00:29:01.620 | That included, again, massive stars that they would explode again, but also the little ones

00:29:07.460 | that keep on living, right?

00:29:10.380 | And then the massive ones, again, exploded supernova, so they provide, again, another

00:29:14.420 | sprinkle of heavier elements.

00:29:16.940 | And so over time, all the elements in the periodic table have been built up.

00:29:21.780 | There have been other processes, for example, neutron star mergers and other exotic supernovae

00:29:27.620 | that have provided elements heavier than iron, all the way up to uranium, from very early

00:29:33.060 | on.

00:29:34.060 | We're still trying to figure out those details.

00:29:36.660 | But I always say pretty much all the elements were done from day three.

00:29:44.140 | - So iron is where, once you get to iron, you got all the fun you need, most of the

00:29:50.060 | fun.

00:29:51.060 | - Yes, I know.

00:29:52.060 | I really like the heavier elements, gold, silver, platinum, that kind of stuff.

00:29:58.820 | - For personal reasons or for star formation?

00:30:00.940 | - Well, both.

00:30:03.380 | - What's the importance of these heavier metals in the evolution of the stars?

00:30:08.660 | - So they're the spice of life, right?

00:30:13.040 | So every supernova gives you elements up to iron.

00:30:17.020 | That's cool, but at some point it gets a little bit boring, because that always works.

00:30:22.440 | But that's the baseline.

00:30:23.460 | We need that.

00:30:25.620 | And that's certainly what came out of the first stars, and then all the other supernova

00:30:30.300 | explosions that followed with every generation.

00:30:32.860 | And it took about a thousand generations, give or take, until the sun was made.

00:30:38.260 | So the sun formed from a gas cloud that was enriched by roughly a thousand generations

00:30:44.100 | of supernova explosions, and that's why the sun has the chemical composition that it has,

00:30:51.820 | and somehow the planets were made from that as well.

00:30:54.980 | - So the supernova explosions of the many generations are creating more and more complex

00:30:58.700 | elements.

00:30:59.700 | - No, it just goes all the way up to iron, and then it's a little bit more of all of

00:31:06.220 | these elements.

00:31:07.220 | - Just more.

00:31:08.220 | - Yeah, it's one sprinkle, then another, and it just kind of adds up, right?

00:31:12.420 | Now the heavy elements form in very different ways.

00:31:14.900 | They are not fusion-made.

00:31:17.100 | They are made typically through neutron capture processes, but for that you need seed nuclei,

00:31:23.260 | particularly iron or carbon or something.

00:31:26.040 | So the supernova-made elements are very good seed nuclei for other processes that then

00:31:31.340 | create heavy elements.

00:31:33.100 | And because they cannot be made everywhere, some of my stars have huge amounts of these

00:31:41.180 | heavy elements in them, and they tell us in much more detail, "Something really interesting

00:31:47.820 | happened somewhere."

00:31:49.820 | - Well, wait, I thought the really old ones we would not have.

00:31:53.580 | So what does that mean if the old--

00:31:55.180 | - Ah, yes, important clarification.

00:31:57.660 | So the stars that we are observing today, these old ones, they formed from the gas,

00:32:05.540 | and the question is, what enriched that gas?

00:32:09.940 | So it could have been just a first star dumping their elements into that gas all the way up

00:32:16.220 | to iron.

00:32:17.220 | - Right.

00:32:19.060 | - And we have found some stars that we think are second-generation stars.

00:32:23.180 | So they formed from gas enriched by just one first star.

00:32:28.300 | That's super cool.

00:32:29.300 | - Yeah.

00:32:30.300 | - Then we find other old stars that have a much more complicated heavy element signature,

00:32:38.060 | and that means, okay, they're probably formed in a gas cloud that had a few things going

00:32:43.900 | on, such as maybe a first star, maybe another more normal supernova, and maybe some kind

00:32:52.340 | of special process like a neutron star merger that would make heavy elements.

00:32:58.500 | And so they created a local chemical signature from which the next-generation star then formed,

00:33:06.580 | and that is what we're observing today.

00:33:08.700 | So all these old stars basically carry the signature from all these progenitor events,

00:33:16.900 | and it's our job then to unravel, okay, which processes and which events and how many may

00:33:23.500 | have occurred in the early universe that led to exactly that signature that we observe

00:33:28.220 | 13 billion years later.

00:33:29.900 | - Is it possible to figure out the number of generations that resulted in these stars?

00:33:36.060 | - Well, we think we can sort of say, okay, this was like second generation or third,

00:33:42.260 | because the amounts of heavy elements in the stars that we observe is so tiny.

00:33:50.900 | One normal supernova explosion is actually already basically too much.

00:33:54.420 | It would give us too much of it.

00:33:57.060 | And the thing is, you can never take away things in the universe.

00:34:00.100 | You can only add.

00:34:01.140 | There's no cosmic vacuum cleaner going around sucking things away.

00:34:08.100 | Black holes are probably the closest to that, but they would have taken the whole star.

00:34:12.260 | - Yeah, they'd take the whole thing, not just a little bit of it.

00:34:13.580 | - They wouldn't take stuff out of the gas, you know.

00:34:17.380 | So we have maybe 10 stars or so now where we are saying they contain so little of these

00:34:26.340 | heavy elements that there must be second generation because how else would you have made them?

00:34:33.340 | And again, I want to stress that the elements that we observe in these stars were not made

00:34:38.300 | by the stars themselves that we observe.

00:34:41.060 | That's just a reflection of the gas cloud.

00:34:42.780 | So we don't actually, I had to say that because I love stars.

00:34:46.180 | At the end of the day, we don't really care for the stars that we're observing.

00:34:48.980 | We care for the story that they're telling us about the early universe.

00:34:52.460 | - So yeah, so the stars are kind of a small mirror into the early universe.

00:34:59.340 | And so what are you detecting about those stars?

00:35:00.980 | Can you tell me about the process of archeology here?

00:35:04.260 | What kind of data can we possibly get to tell the story about these heavy elements on the

00:35:09.940 | stars?

00:35:10.940 | - Yeah, it depends really on what star you find.

00:35:14.900 | There are many different chemical signatures.

00:35:19.620 | We actually pair up these days our element signatures with also kinematic information,

00:35:27.460 | how the star moves about the galaxy.

00:35:30.020 | That actually gives us clues as to where the star might have come from.

00:35:35.900 | Because again, all these old stars are in the galaxy, but they are not off the galaxy.

00:35:41.580 | That's a small but important distinction.

00:35:43.740 | So they all came from somewhere else.

00:35:45.220 | - So you can rewind back in time to kind of estimate where it came from.

00:35:48.660 | - Yeah, so we can't really say, "Oh, it came from that dwarf galaxy."

00:35:51.980 | But interestingly enough, just a few days ago, I submitted a paper with three women

00:35:57.340 | undergrads.

00:35:58.340 | It was so good to work together.

00:36:01.020 | And we found a sample of stars that have very, very low abundances in strontium and barium,

00:36:09.020 | so very heavy elements.

00:36:11.320 | And I had a hunch for a while that these stars would probably be some of the oldest.

00:36:17.300 | Because as I said, heavy elements give you extra information about special events.

00:36:23.600 | And again, finding something that's really low means that must have happened either really

00:36:31.660 | early on or in a very special environment, right?

00:36:35.820 | Because we can only ever add.

00:36:37.300 | So if you find something that's incredibly low in terms of the abundance, maybe just

00:36:42.500 | one event contributed that max.

00:36:45.640 | So we looked at the kinematics, how are these stars moving, and they're all going the wrong

00:36:51.860 | way in the galaxy.

00:36:55.980 | How is that possible?

00:36:57.180 | Well, it is possible because consider, now we come back to the proto-galaxy.

00:37:02.140 | The proto-galaxy was like a beehive.

00:37:03.780 | It just didn't really know what it was or what it wanted to become when it grew up.

00:37:08.940 | And it was absorbing all these little galaxies to grow fast.

00:37:12.660 | Some galaxies, some absorbed galaxies were thrown in going the main way, and some came

00:37:19.460 | in the wrong way.

00:37:20.980 | It happens.

00:37:23.420 | But this could only happen early on when there wasn't left and right and up and down.

00:37:29.760 | So stuff would come in from all ways.

00:37:31.400 | So now, 13 billion years later, we're looking...

00:37:34.940 | They're still doing it.

00:37:35.940 | Yeah, A, they're still doing it.

00:37:37.580 | But B, we just looked for stars that have low strontium and barium abundances, and then

00:37:43.460 | we look at the kinematics, and lo and behold, they're all at hundreds of kilometers per

00:37:48.620 | second going the wrong way.

00:37:50.540 | It's like, dude, you must have come in really early on from somewhere else.

00:37:55.380 | So we call this retrograde motion.

00:37:58.260 | That's a clear sign of accretion, so something that has come into the galaxy.

00:38:04.020 | And because they are so fast, and it's really all of them, that must have happened early

00:38:10.540 | on.

00:38:11.540 | You can't throw a galaxy into the Mickey Ray right now the wrong way.

00:38:14.900 | It eventually will turn around.

00:38:16.380 | - Can you actually just, on a small tangent, speak to the three women undergrads, this

00:38:21.460 | little...

00:38:22.460 | It's pretty cool that you were able to use a hunch to find this really cool little star.

00:38:29.740 | Yeah, what's the process like, especially with undergrads?

00:38:32.540 | I think that would be very interesting and inspiring to people.

00:38:35.020 | - Yes, it was a wonderful little collaboration that actually emerged in the fall.

00:38:42.580 | So I really like working with undergrads and grad students, postdocs, and I came up with

00:38:49.220 | a new concept for a class at MIT where I wanted to integrate the research process into the

00:38:55.940 | classroom because sometimes people find it really hard to call, email a professor, "Hey,

00:39:05.180 | I'm this and that person, and I'm interested in your research.

00:39:07.820 | Could I possibly come?"

00:39:10.540 | And I wanted to streamline that and give, not just trial, how it would work to provide

00:39:19.060 | a sort of the safe confines of a classroom where you just sign up and do research in

00:39:25.140 | a very structured way.

00:39:27.820 | And I developed it, it was a lot of work, a little bit more than I thought, to map up

00:39:34.860 | an entire research project basically from scratch in 10 worksheets so that they could

00:39:40.980 | do it, again, in a very structured and organized fashion.

00:39:43.980 | - Oh, so you created this whole framework for them to do it?

00:39:46.420 | - Yes, the whole thing.

00:39:49.100 | But the promise was, you come sign up for my class in teams of two.

00:39:54.180 | You each get your own old star that has not been analyzed before.

00:39:58.100 | I don't know what the solution is because in research, we don't look up the solution

00:40:02.740 | at the end of the book.

00:40:03.740 | We do not know what we're going to find.

00:40:05.900 | Our job is to do the work and then to interpret the numbers because our job as scientists

00:40:11.860 | is to find the story.

00:40:15.380 | Anyone can crunch numbers, anyone.

00:40:17.860 | It's kind of complicated sometimes, but it's doable, right?

00:40:23.940 | But coming up with a story, when you only have three puzzle pieces, what does the puzzle

00:40:28.620 | look like?

00:40:31.020 | You have to be a little bit bold, you need to have some experience, and you need to kind

00:40:37.140 | of see the universe in 3D.

00:40:38.900 | You just need to kind of go for it.

00:40:40.520 | And that's the beautiful thing, I really love that.

00:40:42.540 | - And so this was a story of weird kinematics going the wrong way combined with this particular

00:40:48.260 | weird signature in terms of the heavy elements.

00:40:50.700 | - Yeah, exactly.

00:40:51.700 | - And you have to come up with a story about that.

00:40:52.700 | - Yes, and so the story of that paper is now, usually I don't say I find the oldest stars.

00:41:00.700 | When I talk to my research colleagues, I talk to them about we find the chemically most

00:41:04.860 | pristine stars because that's actually what we measure, the chemical abundance that tells

00:41:09.260 | us, okay, it must have been second or third or fifth generation of stars, right?

00:41:13.900 | But these low strontium stars that go in the wrong way, like they're getting paid for it,

00:41:18.820 | they must be the oldest stars that came into the galaxy because they formed before the

00:41:25.580 | galaxy was the Milky Way, right?

00:41:29.660 | And it's so cool, and it was so wonderful.

00:41:31.780 | So this class, it went so well in the fall.

00:41:35.020 | I had nine people sign up.

00:41:38.060 | That's not unusual for a class, a specialty class at MIT, so small number.

00:41:42.440 | It was eight women, and they were so into it that I said, "Okay, let's use this opportunity.

00:41:50.340 | You're gonna do some extra work with me, and we're gonna publish this."

00:41:54.540 | - Try to publish.

00:41:55.540 | - Yes.

00:41:56.540 | - I also like that you're using the terminology of chemically more pristine.

00:42:01.060 | When I'm talking to younger people, I'll just say that I'm more chemically pristine than

00:42:04.980 | them.

00:42:05.980 | I like that description of age.

00:42:08.360 | So there's this term of metal-poor stars.

00:42:11.580 | So most of these old stars are going to be metal-poor.

00:42:13.700 | - Yes, I search for the most metal-poor stars.

00:42:16.700 | - And what does that, can we just define?

00:42:18.700 | - Yeah, what does that mean?

00:42:20.260 | I don't know who came up with this.

00:42:22.380 | I would love to know, but the universe is a complicated place.

00:42:27.620 | So many decades ago, someone clever came up with the idea to say, "Let's simplify things

00:42:34.660 | a little bit.

00:42:35.660 | Let's call hydrogen X, helium Y, and all the other elements combined, metals, Z."

00:42:46.260 | When I give public talks, I always ask, "Is there a chemist in the audience?

00:42:50.180 | Let me just tell you, neon is a wonderful metal."

00:42:52.900 | And they're like, "Oh my God, what's she saying?"

00:42:56.340 | I'm an astronomer, I'm not a chemist, so I'll get away with it.

00:42:59.680 | So if you just roll with it for a moment, all the elements except hydrogen and helium

00:43:04.540 | are called metals.

00:43:06.660 | Now if we look again at the concept of chemical evolution, it means more and more of all the

00:43:13.040 | elements, everything higher than hydrogen and helium gets produced slowly but surely

00:43:18.220 | by different types of stars and events.

00:43:21.800 | So that's a monotonously increasing function.

00:43:27.700 | And so we look for the stars that have the least amounts of heavy elements in them, because

00:43:33.140 | that means we are going further and further back in this process, in that function, almost

00:43:39.220 | all the way to the very beginning, and that is the first stars, right?

00:43:43.540 | They started that process.

00:43:46.180 | That's why I said it was such an important transition phase, because we call the post-Big

00:43:53.780 | Bang universe pristine, just hydrogen and helium, and after that the mess started.

00:43:57.860 | As soon as you add elements to it, things kind of get a little out of hand.

00:44:04.040 | That ends in this beautiful variety that we have everywhere these days.

00:44:09.220 | Yeah, and you're looking at the very early days of the introduction of the variety.

00:44:13.100 | Yes, exactly, when it was still a little bit more organizable.

00:44:20.020 | But the variety of different types of metal-poor stars we have is stark.

00:44:24.740 | Many different types of stars, many patterns we have sort of identified, but there are

00:44:28.940 | still crazy ones out there that we're still trying to kind of fit in.

00:44:34.180 | - So what kind of stars have been discovered?

00:44:35.660 | So you've already a while ago helped discover the star HE 1327 2326, great name.

00:44:46.340 | - Yes.

00:44:47.340 | - And HE 1523 0901.

00:44:51.700 | What can you say about these stars and others that have been found?

00:44:55.700 | - I love them.

00:44:56.700 | They're my baby stars.

00:44:58.460 | - What do you call your baby stars?

00:45:01.500 | - Well, I'm probably the only one who can spit out these names without cheating.

00:45:05.940 | - Are those nicknames?

00:45:06.940 | - Well, no, that's...

00:45:07.940 | - It's not allowed?

00:45:08.940 | Okay.

00:45:09.940 | - Well, some colleagues at conferences have just called them Anna Star or Fribo Star,

00:45:15.300 | because they didn't want to learn the phone number.

00:45:18.820 | You know, I get it.

00:45:19.820 | - The phone number, yeah.

00:45:20.820 | - And these numbers are actually based on older sets of coordinates for these stars.

00:45:25.500 | So they, yes, the minus in the middle means that they're in the Southern Hemisphere.

00:45:29.740 | So negative is in the Southern Hemisphere, positive is in the Northern.

00:45:33.860 | And then 13 and 15 means that sort of observable in the middle of the year.

00:45:37.340 | - Okay, so it has to do with the observation and where it was observed.

00:45:40.260 | - Yes, yes, yes.

00:45:41.620 | But they have very different stars, both absolutely significant career defining actually for me,

00:45:50.100 | but really pushed the envelope in very different ways.

00:45:54.020 | So HG 1327, the first one that you mentioned, that was the second, second generation star

00:46:00.020 | that we found.

00:46:02.060 | And you know, usually people say like, oh, the first one is the big one and the rest

00:46:06.260 | is nobody cares.

00:46:08.420 | But to us, it proved that yes, we can do it.

00:46:13.580 | Because one, astronomers live in this sort of way of, you know, there are a lot of serendipitous

00:46:19.660 | discoveries and we, that's really great, but we need to show that we can do it again.

00:46:26.500 | - Reliably.

00:46:27.500 | - Because then we're onto something and it's not just some kind of weird quirk.

00:46:31.180 | And there are a lot of quirks in the universe, but we want to know is that a real thing?

00:46:35.700 | Does that happen regularly?

00:46:36.940 | Is there something that we can learn?

00:46:38.820 | Is that a piece of the story?

00:46:41.900 | And so finding the second one that was even a little bit more extreme than the first one

00:46:46.140 | really showed, yes, our search techniques work, we can find these stars.

00:46:51.660 | They provide an important part to the story in the sense that if we had more than two

00:46:59.500 | stars, and by now we have about 10-ish or so, what do they tell us about the nature

00:47:05.900 | of the very first stars?

00:47:09.500 | And what we found, again, working with the theorists, of course, who run these supernova

00:47:15.060 | models is that, so actually let me, before I get into this, these two stars had huge

00:47:23.500 | amounts of carbon relative to iron.

00:47:26.900 | So we usually use iron as a reference element for what we call the metallicity, so the overall

00:47:34.260 | metal content, the overall amount of heavy elements in it.

00:47:38.220 | So that's why it's called iron deficient.

00:47:40.820 | That's right.

00:47:41.940 | So these stars are incredibly iron deficient, which means they must be of the second generation

00:47:47.100 | because there was, and interestingly enough, there was this discrepancy.

00:47:55.260 | A normal supernova, until then, we thought would get us so much iron, you know, and you

00:48:02.460 | would distribute that in the gas cloud and then you would form this little star that

00:48:06.260 | we're observing, but the iron abundance that we measured was actually much lower than that.

00:48:10.860 | And I already mentioned, you can't take things away.

00:48:13.540 | That must mean these early massive POP3, we call them Population 3, the first stars, they

00:48:20.140 | must have exploded in a different way than we previously thought.

00:48:23.180 | They can't output as much iron because they just can't.

00:48:28.420 | Otherwise it wouldn't match our observations.

00:48:32.020 | And so that's when we started to work with several theory groups on supernova yields.

00:48:40.080 | So what comes out of...

00:48:41.820 | From the explosion of the supernova?

00:48:43.660 | That's cool.

00:48:44.660 | Supernova yields.

00:48:45.660 | And so this one was not yielding much iron.

00:48:48.020 | Well, we needed to concoct a theoretical supernova that made less.

00:48:54.860 | And it's actually surprisingly difficult because you can always add more in the universe, right?

00:48:59.500 | But you can't take stuff away.

00:49:02.140 | So Japanese colleagues kind of came up with the idea of a fainter supernova that just

00:49:09.060 | doesn't have enough oomph when it explodes.

00:49:13.380 | So somehow there's less iron coming out.

00:49:17.100 | But at the same time, then these stars showed huge overabundances of carbon, a thousand

00:49:22.120 | times more carbon.

00:49:24.260 | So how do you now get a thousand times more carbon out of these poor first supernovae?

00:49:30.620 | That was the theoretical challenge.

00:49:32.460 | And because we didn't have just one star, but two, that really spurred the field to

00:49:39.300 | think about what was the nature of the first stars?

00:49:42.900 | How did they explode?

00:49:45.160 | What are the implications?

00:49:46.460 | Because if they are not as luminous and bright and energetic, that has consequences for these

00:49:53.100 | early proto-galaxies in which they must have been located in terms of blowing the gas out,

00:50:00.260 | let's say, and disrupting the system.

00:50:02.540 | So much higher chance for the earlier system to stay intact for longer, right?

00:50:07.580 | So there's a whole tale of consequences.

00:50:10.460 | And this is what I mean with we need to find the story because you do one thing and it's

00:50:16.900 | like the dominoes, there are consequences everywhere and suddenly you have a different

00:50:19.540 | universe, right?

00:50:20.540 | So what could possibly be a good explanation for something that yields a lot of carbon

00:50:26.580 | and doesn't yield a lot of iron?

00:50:28.580 | Well, it's not so much an explanation, more like finding a mechanism for what happens

00:50:33.980 | in supernovae and the official term, what was sort of, as I said, cooked up in order

00:50:40.740 | to explain the observation.

00:50:42.500 | And we have, by the way, found a whole bunch more of these stars, so that holds.

00:50:46.300 | And it's called a fallback mechanism.

00:50:48.060 | So actually during the supernova explosion, a massive black hole emerges.

00:50:54.780 | And so some of the material falls back onto the black hole.

00:50:58.340 | So here is a vacuum cleaner now plopped into the middle, right?

00:51:03.140 | - Like a temporary one that just cleans up some of the elements?

00:51:05.660 | - Well, sort of, right?

00:51:06.660 | Because if you think of the, we haven't talked about this yet, but if you know what a star

00:51:11.300 | looks like, a massive star looks like in its interior before it explodes, you have hydrogen

00:51:18.020 | and helium still on the outskirts, and then you have layers of heavy and heavy elements

00:51:22.580 | all the way up to iron.

00:51:23.580 | So you have an iron core in the center.

00:51:28.060 | And because you can't get any energy out of iron when you want to fuse to iron atoms anymore,

00:51:33.100 | that's when the supernova explodes, or occurs really.

00:51:36.860 | It's actually an implosion first, and then you have a bounce of the sort of neutron star

00:51:42.620 | phase that occurs in the process.

00:51:45.460 | And then it gets disrupted.

00:51:46.460 | - That is so awesome.

00:51:47.460 | - Yeah, it's like this giant basketball, and then, whoa, it all goes out.

00:51:53.460 | - So implosion first, explosion after.

00:51:55.340 | - And so in the process, right, if you make your black hole basically big enough, it will

00:51:59.700 | suck away some of the iron because that's the closest in terms of the layers.

00:52:05.500 | You hold onto it, you don't let it escape, and carbon is much further out, you let it

00:52:11.140 | all go.

00:52:12.140 | - Nice.

00:52:13.140 | - And so--

00:52:14.140 | - So that explains why you can have a big oomph and not much iron yield.

00:52:17.860 | - Yes, yes.

00:52:18.860 | - So is this explained, the HE 1327?

00:52:21.700 | - Correct.

00:52:22.700 | - And others like it?

00:52:25.380 | - Yes.

00:52:26.380 | So there's, it's well established now that the lower the iron abundance of the stars

00:52:31.980 | are, the higher the carbon sort of gets.

00:52:35.420 | And carbon is such an interesting element in that regard.

00:52:40.860 | If we come back to the formation of the first LOMAS stars, right, so we had the hotter gas,

00:52:47.420 | just hydrogen and helium, that made the first stars.

00:52:50.140 | There were 100 solar masses or so because the gas couldn't cool enough, so they were

00:52:54.980 | big and puffy.

00:52:57.820 | Carbon then, coming from the first stars, probably led to enough cooling in these gas

00:53:03.940 | clouds that enabled the formation of the first LOMAS stars.

00:53:09.220 | So think about what happened if there wouldn't have been any carbon, or the properties of

00:53:13.540 | the carbon atom would be different.

00:53:15.580 | It would not have cooled the gas in such significant ways, perhaps.

00:53:20.580 | There wouldn't be any LOMAS stars.

00:53:23.620 | We wouldn't be here today, right?

00:53:25.780 | And we're carbon-based, and so I think carbon is really the most important element in the

00:53:30.020 | universe for a variety of reasons, because it has enabled this whole evolution that we're

00:53:35.420 | now observing and literally seeing in the sky, and it's really fascinating.

00:53:40.180 | - So combined with the fact that you have the ion deficient, so all of that is probably

00:53:43.780 | important to creating humans.

00:53:46.420 | - Yeah, yeah, we need all the elements, but if you don't have stars, like the sun, small

00:53:52.380 | stars that can actually host planets, that have long lifetimes, you need long, long lifetimes

00:53:57.380 | if you want to have a stable planet and develop humans.

00:54:01.340 | - So carbon is kind of important in many ways.

00:54:04.380 | - Yes, yes.

00:54:06.180 | - This is perhaps an interesting tangent, if I could just mention that you interviewed

00:54:12.260 | a military dressel house, Carbon Queen, the remarkable life of the nanoscience pioneer.

00:54:20.020 | Is there something you could say about the magic of Carbon and the magic of Millie?

00:54:25.940 | - Well Millie was certainly magic.

00:54:28.700 | She was a professor at MIT for many decades.

00:54:32.340 | I met her a number of times.

00:54:34.900 | Her photograph, actually a young and an older Millie is still on the wall every time I step

00:54:40.180 | out of the elevator in one of the buildings I see it.

00:54:44.540 | She pioneered all sorts of carbon nanowork, so she was a material scientist, very far

00:54:54.460 | removed from what I do on a daily basis.

00:54:58.140 | But yes, carbon has amazing properties when you study it and again, that's indeed another

00:55:03.540 | aspect of why carbon is so fascinating, not just in the cosmos but also for us, making

00:55:12.620 | us, creating us in the way that we can use it.

00:55:17.820 | It's wonderful.

00:55:18.820 | - Do you sometimes think about this chemical evolution in this big philosophical way that

00:55:23.740 | we're the results of that chemical evolution, like we're made of this stuff, we're made

00:55:29.900 | of carbon?

00:55:30.900 | - Yes, we're made of star stuff.

00:55:31.900 | - Yeah, and it came-- - Cross-check and go right.

00:55:32.900 | - I mean it's almost like a cliche statement but it's also a materials, a chemical, a physics

00:55:42.100 | statement that we came from hydrogen and helium and that somehow this formation has created

00:55:47.620 | this interesting complexity of soup that made us.

00:55:52.420 | What are we supposed to make of that?

00:55:54.860 | Like what, did we just get really lucky?

00:55:56.300 | Why did we get all this cool stuff?

00:55:59.300 | - Yeah, that's a good question.

00:56:01.620 | - I don't think it's a question that has an answer, I keep just asking why.

00:56:06.140 | But it's just this incredible mystery, so much cool stuff had to happen, so much, sorry,

00:56:12.780 | hot stuff had to happen to create us.

00:56:15.740 | - And so much could have gone wrong and there would have been another outcome and it's actually

00:56:20.940 | amazing how many things kind of fell in place.

00:56:24.260 | I mean maybe that's all sort of self-deterministic in some ways, right?

00:56:29.180 | We are who we are because that was the path.

00:56:33.060 | Maybe we would have ended up being robots, I don't know.

00:56:36.940 | But it's certainly wonderful to, you know, as scientists for us to help contribute unraveling

00:56:44.060 | our cosmic history, right?

00:56:46.420 | I always say the biological evolution on Earth was absolutely facilitated by the chemical

00:56:53.860 | evolution of the universe, right?

00:56:55.340 | And one doesn't go without the other.

00:56:57.820 | - And that evolution-- - From a human perspective.

00:57:00.180 | - That evolution seems to be creating more and more complexity.

00:57:03.540 | The kind of interesting clumping of cool stuff seems to be accelerating and increasing.

00:57:11.180 | It's hard not to see as humans that there's some kind of purpose to it, like a momentum

00:57:16.500 | towards complexity and beauty, you know?

00:57:20.380 | - Well beauty's in the eye of the beholder.

00:57:23.980 | But yes, everything gets more complicated.

00:57:26.360 | - But there's also a beauty to the chemically pristine universe in the early days.

00:57:30.420 | - There certainly is, yes.

00:57:32.460 | I love the desert with its nothingness.

00:57:35.860 | It has so much aesthetics and appeal.

00:57:39.340 | We came from nothing, we'll return to nothing.

00:57:41.780 | So what about HE 1523?

00:57:44.940 | What's exciting?

00:57:45.940 | A red giant star.

00:57:49.140 | - Yes.

00:57:50.460 | - That's another one of your babies.

00:57:52.060 | - Yes.

00:57:53.060 | - 13.2 billion years old.

00:57:55.540 | - Yeah, so that one isn't quite as iron deficient as the other one.

00:58:00.020 | So probably not a second generation star, but easily second, third, fourth, fifth or

00:58:06.260 | so.

00:58:07.260 | So you can't really pin it down, but it's also not super important for us.

00:58:12.700 | What is important is that that star has a very different chemical composition in a sense

00:58:19.420 | that yes, we have all the elements up to iron there.

00:58:22.760 | They have sort of normal ratios, which means kind of the same as most other old stars and

00:58:31.900 | not too different from the Sun or at least different in quantifiable ways.

00:58:39.180 | But it has this huge overload of very heavy elements.

00:58:43.860 | And what was so nice about that star in particular was that I could measure the thorium and the

00:58:48.180 | uranium abundance.

00:58:50.900 | And again, that was the second of its kind, but the uranium abundance could be more well

00:58:58.900 | determined.

00:58:59.900 | So we had a better grasp on that.

00:59:01.620 | Now why are thorium and uranium interesting?

00:59:05.660 | They are radioactive elements.

00:59:09.060 | They decay.

00:59:11.400 | Thorium has a half-life of 14 billion years, I believe, and uranium of 4.7, which to folks

00:59:20.160 | on us on Earth is a really long time, but those kind of timelines are really good when

00:59:25.580 | you want to explore the early universe.

00:59:29.660 | So there are two questions now that kind of come to mind.

00:59:34.940 | Where do these elements come from and what do they tell us?

00:59:40.060 | And as we know, these heavy elements are made in a specific process.

00:59:46.740 | It's a neutron capture process, usually referred to as the R process for rapid neutron capture

00:59:52.760 | process.

00:59:54.140 | We talked about seed nuclei before, right?

00:59:56.380 | So we still don't exactly know where this process can occur.

01:00:00.480 | So you have, let's say, a lone iron atom somewhere, and it is in an environment where you have

01:00:07.380 | a strong neutron flux, which means there must be lots of neutrons around.

01:00:12.340 | And again, when we talk about the site, we can surmise and ponder where that might be

01:00:17.620 | the case.

01:00:19.020 | But you have this iron atom and you bombard it with neutrons and you do it incredibly

01:00:23.300 | fast.

01:00:24.300 | Now what happens in the process?

01:00:26.340 | That iron atom, you collect lots of neutrons, it becomes really big and unstable.

01:00:32.620 | So it's a heavy neutron-rich nucleus that wants to decay because it's not stable, it's

01:00:39.580 | way too big.

01:00:41.620 | And so let's say you add only one neutron to it, that would already make it unstable.

01:00:48.260 | So it has a characteristic decay time that's called the beta decay timescale, so it will

01:00:53.940 | decay to a stable nucleus.

01:00:55.540 | So the neutron will convert to a proton and that makes it stable.

01:01:00.380 | If you now bombard lots and lots and lots of neutrons onto that seed nucleus within

01:01:05.860 | that timescale of the beta decay, that's how you get to this huge, fat, neutron-rich nucleus

01:01:12.640 | that then wants to decay, right?

01:01:14.880 | So the rapid processes, you have your seed nuclei, they get bombarded, you create these

01:01:20.260 | really heavy neutron-rich nuclei, they're heavier than uranium even, the neutron flux

01:01:26.500 | stops and then all these heavy nuclei, they decay.

01:01:31.460 | And they make all these stable isotopes that we know of, all the way up to thorium and

01:01:37.540 | uranium.

01:01:38.540 | So that rapid nuclei decay is what creates all the funnels.

01:01:43.020 | Correct.

01:01:44.020 | And the whole thing is done within two seconds.

01:01:48.260 | So just to add to the rapid here, literally the snapping on my hand, it's all there.

01:01:55.820 | In my talks, I often have this nice simulation that illustrates this creation of these heavy

01:02:03.020 | nuclei, and I always say, "This is the only simulation you will ever see that's slower

01:02:09.020 | than real time."

01:02:10.020 | Because in astronomy, we show, "Oh, this is how a galaxy forms, 13 billion years in

01:02:16.020 | 30 seconds," really short, right?

01:02:19.260 | This is the opposite.

01:02:20.740 | Me showing you this, the elements are long made.

01:02:24.080 | So where and when does this happen, does this process happen?

01:02:26.980 | So you need the strong neutron flux.

01:02:31.180 | That's the clumping of the neutrons.

01:02:33.180 | Yes, that's right.

01:02:34.980 | And so there are not that many options, right?

01:02:37.460 | So where do you find lots of neutrons in the universe?

01:02:40.020 | Well, it's neutron stars, right?

01:02:42.660 | Neutron stars form in the making of supernovae, of the explosions.

01:02:48.020 | Okay, so maybe some of this heavy material gets sort of made in the making of the supernova

01:02:52.780 | explosion and then gets expelled.

01:02:56.180 | Or you have neutron stars, so if the neutron star, I mean, usually that's the leftover

01:03:03.260 | of the supernova.

01:03:04.260 | If you have two from a binary pair, so stars usually actually show up in pairs, and so

01:03:10.340 | it's not too unusual to create a pair of neutron stars that will still orbit each other after

01:03:17.980 | both of their progenitor stars have exploded.

01:03:21.460 | And those two neutron stars will orbit each other diligently.

01:03:25.740 | But as we know now, thanks to LIGO, the Gravitational Wave Observatory, I mean, we know already

01:03:32.500 | that before but now it's been measured by LIGO, is that these two neutron stars, they

01:03:38.740 | will orbit each other for like forever, but in the process they will lose energy.

01:03:44.100 | So that orbit is what we call the orbit decays, and eventually the two neutron stars will

01:03:49.980 | merge and that results in an explosive event that has roughly the energy of a supernova,

01:03:58.260 | but the process is completely different.

01:04:01.140 | And the cool thing is when these two neutron stars collide, they produce a gravitational

01:04:06.900 | wave signature because neutron stars are super dense objects.

01:04:11.580 | They're like giant atomic nucleuses.

01:04:14.660 | So there's a lot of interesting physics happening already, and so if you basically form a super

01:04:19.280 | neutron star by smashing two into each other, more interesting physics happens, and that

01:04:26.620 | means that there's this ripple sent out into the space-time continuum basically, you know,

01:04:36.140 | what do people say, the ripples of space-time, you know, it's like you drop a rock into water,

01:04:41.300 | right?

01:04:42.300 | You see the waves coming, so that's exactly what happens when two neutron stars merge,

01:04:47.740 | and this is neutrons galore, right?

01:04:49.900 | It's really violent to smash two neutron stars that are so dense already into each other.

01:04:56.900 | And in 2017, one of these events occurred, and the LIGO and Virgo Gravitational Wave

01:05:05.460 | Observatories, they detected that, and then the astronomers pointed their telescopes in

01:05:10.820 | that direction, and they indeed observed what we call the electromagnetic counterpart.

01:05:16.320 | So there was something seen in the sky that faded over the course of two weeks, and that

01:05:24.020 | light curve, that light was exactly what you get when you create all these heavy neutron-rich

01:05:32.200 | nuclei in the R process, and then the neutron flux stops, and then it takes about two or

01:05:37.620 | three weeks for most of them, of these nuclei, to decay to stability.

01:05:43.220 | So we saw, the astronomers saw in this electromagnetic counterpart, the nucleosynthesis of heavy

01:05:51.140 | elements occurring, and that's just awesome.

01:05:55.220 | - That's amazing.

01:05:56.220 | - So awesome.

01:05:57.220 | - So that's electromagnetic counterpart to the gravitational waves that were detected

01:06:01.180 | with two neutron stars colliding aggressively, violently, to create a super neutron star,

01:06:11.340 | and that's where you get all the neutrons and neutron flux somehow, and then the whole

01:06:14.940 | shebang that happens in two seconds and creates a bunch of--

01:06:17.540 | - So that confirmed that one of the sites, for sure, is, for the R process to occur,

01:06:24.260 | is neutron star mergers.

01:06:26.460 | Interestingly enough, I have to mention this here, a year prior, in 2016, my former grad

01:06:32.060 | student Alex G. and I, we discovered a small dwarf galaxy that is currently orbiting the

01:06:40.220 | Milky Way, it's called Reticulum 2, that was full of ancient iron-deficient stars that

01:06:48.060 | also had a strong signature of these heavy elements, exactly like He 1523.

01:06:54.700 | We weren't looking for that.

01:06:56.260 | I actually wanted to prove that they had really low levels of heavy elements, because that's

01:07:01.180 | what we had seen in all the other dwarf galaxies, and I was dead set on showing that that is

01:07:08.620 | yet the case again, and that that is a typical signature of early star formation.

01:07:13.540 | We already talked about low strontium and barium abundances and the oldest stars, right?

01:07:18.100 | This is what we had seen anecdotally in the ancient dwarf galaxies that are surrounding

01:07:22.520 | us.

01:07:23.520 | - That's an ancient dwarf galaxy, that dwarf galaxy has a bunch of ancient stars in it.

01:07:27.900 | - Yes, yes.

01:07:29.020 | And so now we find Reticulum 2, and it has these, the stars show the signature of the

01:07:35.580 | rapid neutron capture process, the R process, and we are like, okay, these stars are located

01:07:42.740 | in a dwarf galaxy right now, we have environmental information, they are not lost in the galaxy

01:07:47.780 | where we don't know where they actually came from.

01:07:49.700 | No, we know these stars were formed in that galaxy because they're still in it.

01:07:55.080 | And that we already deduced from that, that it must have been a neutron star merger that

01:07:59.400 | went off in Reticulum 2 at early times, that polluted the gas from which all our little

01:08:04.920 | stars formed.

01:08:05.920 | - Can you speak to what a dwarf galaxy is?

01:08:07.920 | Can you speak to what this Reticulum 2 dwarf galaxy is that is orbiting the Milky Way galaxy?

01:08:12.920 | It's going to be eaten by it, presumably?

01:08:15.120 | - It totally is going to be eaten.

01:08:17.480 | I can't tell you exactly when.

01:08:20.060 | Yeah, the Milky Way remains surrounded by dozens of small dwarf galaxies.

01:08:25.860 | They're collections of stars.

01:08:28.620 | Some of them, we call them ultra-faint dwarf galaxies because they now only contain, I

01:08:34.020 | don't know, a few thousand stars.

01:08:36.940 | Very very faint.

01:08:37.940 | - They're still detectable?

01:08:39.940 | - Yes, because they're fairly close, and we detect actual individual stars in them.

01:08:45.060 | So I've observed some of the fainter stars.

01:08:48.300 | You possibly observe with current telescopes in these dwarf galaxies because I was like,

01:08:52.460 | I need to know what the chemical composition is because there are leftovers from the early

01:08:57.980 | universe.

01:08:58.980 | They did not get eaten.

01:09:00.920 | So they're still in their native surroundings.

01:09:04.080 | It's like getting the lions in the wild, right?

01:09:06.720 | I got to study those and compare to the counterparts that got eaten and are now in the Milky Way.

01:09:13.680 | And so I...

01:09:14.680 | - But presumably most of those stars, not all of those stars in that dwarf galaxy are

01:09:18.000 | really ancient.

01:09:19.000 | - They're all really ancient because actually, as it turns out, if you have a small galaxy,

01:09:26.120 | there was a process early on in the universe called reionization that kind of heated up

01:09:30.360 | everything.

01:09:32.100 | And together with some supernova explosions in an early shallow, you know, bound system,

01:09:40.240 | all these little systems lost their gas.

01:09:42.500 | It was sort of blown out or it simply evaporated or both, probably both.

01:09:48.200 | And so these systems have been unable to continue to form stars since.

01:09:53.800 | So it's the best for us stellar archaeologists that you could hope for because it's a whole

01:10:01.320 | bunch of stars still sitting there.

01:10:03.160 | It's not just one, it's a whole bunch of them still sitting there ever since and nothing

01:10:07.840 | has literally nothing has happened to them.

01:10:10.120 | They've just been waiting there for us.

01:10:11.820 | - So from the stellar archaeology perspective, what is juicier and more interesting, the

01:10:17.840 | old stars in the outskirts that have been eaten or the outskirts of Milky Way or the

01:10:22.680 | stars in the dwarf galaxies?

01:10:24.840 | What's of all the things you love about the world?

01:10:28.960 | You said you love stars, so which do you love more of your church?

01:10:34.600 | - That's a hard one.

01:10:35.600 | I mean, I love them all, of course.

01:10:38.280 | They serve different purposes.

01:10:40.800 | The stars in the Milky Way, I can get much, much, much better data for them because they're

01:10:45.800 | brighter, they're closer, so they're brighter.

01:10:48.840 | And that tickles my fancy.

01:10:51.880 | - And they have interesting kinematics, presumably.

01:10:54.000 | - Yes, and we can get that.

01:10:55.640 | And so HT 1523, for example, that one is really bright, it's a red giant, so it's intrinsically

01:11:02.760 | bright and it's fairly close.

01:11:04.960 | And so the data I got for that was insanely good and that yielded this uranium detection

01:11:10.200 | and thorium detection.

01:11:12.400 | I can never get that kind of data for dwarf galaxies, though.

01:11:15.560 | So that's a big trade-off.

01:11:17.600 | But the environmental information that we get along with the basic information about

01:11:21.880 | these stars in each dwarf galaxy is really, really valuable in establishing, for example,

01:11:28.520 | the site information, right?

01:11:30.720 | Because the galaxy is still there, so nothing crazy could have happened.

01:11:35.560 | So actually to close that loop, probably some heavy elements come out of supernovae here

01:11:41.720 | and there, but somehow my theory colleagues tell me that a normal supernova just doesn't

01:11:46.960 | have enough oomph to really get an R process going and doing it all.

01:11:50.840 | - So you need these orbiting supernovae.

01:11:54.480 | - We need probably the neutron star mergers or we need a special kind of supernova that's

01:11:59.200 | maybe extremely massive or heavily rotating or does something else funny, right, to really

01:12:03.480 | kind of get that particular process going.

01:12:06.040 | But the normal supernovae don't do it, right?

01:12:08.280 | So only a little bit comes out.

01:12:09.600 | But you could come along and say, "Anna, why don't you just take 100 supernovae together

01:12:14.320 | to build up the yield?"

01:12:16.580 | But then I come along and say, "Look, this dwarf galaxy is still intact today.

01:12:21.120 | If you would have plugged in 100 supernovae into this little system early on, it would

01:12:25.520 | have blown apart.

01:12:26.780 | It would have blown apart past 5 supernovae or 10."

01:12:30.720 | So that's a really important constraint that we have that these systems are still alive,

01:12:34.920 | right?

01:12:35.920 | So it helps us to pin down where certain processes could have possibly happened.

01:12:41.840 | And so it's just a different type of information that we get.

01:12:46.040 | - It'd be amazing if we could talk about the observational aspect of this, the tools of

01:12:50.240 | observation.

01:12:51.580 | So what telescopes have you used, do you use, and what does the data look like?

01:12:57.080 | And I think I've read a few interesting stories about the actual process of day-to-day observation,

01:13:02.680 | a bunch of probably late nights.

01:13:05.520 | - Well, yeah, astronomers are doing it all night long, so we have lots of late nights.

01:13:10.920 | - Can you explain the all-night-long aspect of it?

01:13:14.240 | - Well, let me start by saying I mostly these days use the Magellan telescopes in Chile.

01:13:20.240 | They are 6.5 meter telescope, which means the mirror diameter is 6.5 meter.

01:13:26.800 | It's not the largest that is out there, but it's among the largest.

01:13:31.480 | And I use a spectrograph because I'm a spectroscopist, I don't take pictures.

01:13:39.160 | And that particular spectrograph at that telescope is actually unusually efficient.

01:13:45.820 | So it kind of makes up for the fact that the mirror isn't as large in, let's say, the 8

01:13:49.960 | meter telescopes from the Europeans or so.

01:13:52.840 | So I'm very happy with that.

01:13:54.560 | - Efficiency meaning?

01:13:55.560 | - So many photons get collected sort of per time unit because that's always the limiting

01:14:02.920 | factor.

01:14:06.520 | Prior to the pandemic, we would travel to Chile to do our observations.

01:14:13.000 | Those telescopes are the, that's the last observatory where people were sort of supposed

01:14:17.000 | to travel there and take their own observations.

01:14:19.840 | Most other observatories basically have staff there by now who take the observations for

01:14:25.400 | you.

01:14:26.400 | - So there's the directly, the scientists are specifying where to point the telescope

01:14:32.320 | and sitting there and collecting the data, make sure the data is collected well, the

01:14:36.320 | cleaning of the data, the offloading of the data, all that kind of stuff.

01:14:39.480 | - Yeah, so it's mostly done for them.

01:14:43.320 | Obviously that's super convenient, but it also takes away a central part of what the

01:14:49.920 | work of an astronomer is, which is data collection.

01:14:54.680 | We don't have an experiment in the basement where we can go day and night or whenever

01:14:58.560 | we please and ask a certain question of the apparatus, right?

01:15:04.160 | Let's turn this knob and see what happens.

01:15:06.880 | Let's turn that knob and see what happens.

01:15:08.480 | No, you know, we only have one experiment, which is the universe and what we see is what

01:15:15.120 | we get.

01:15:17.200 | And I think it's so important to take an active role in that.

01:15:21.540 | So I really love going to the observatory.

01:15:24.760 | I've taken many students there over the years to teach them and to just show them what it

01:15:33.160 | means to be an astronomer because you go to these remote mountaintops and it's such a

01:15:39.920 | magical environment and you wait there for the sun to go down and then you get ready

01:15:46.440 | and you look outside and it's such a serene environment.

01:15:53.120 | It's a little bit out of this world.

01:15:55.400 | You're sitting there, so the sun goes down, it's evening, late evening, and what does

01:16:00.240 | it look like?

01:16:01.240 | What are some of the most magical experiences of that process?

01:16:03.840 | Well, you know, when you're on top of a mountain, you know, climbers I guess get to see that

01:16:09.240 | probably, otherwise.

01:16:14.720 | It's very calm and the colors are so beautiful and I always become much calmer when I'm there.

01:16:22.920 | I'm just A, because I'm just there for one purpose only, that's data collection.

01:16:28.920 | I can say no to my emails, I can say no to everything else because I'm observing.

01:16:34.680 | So there's literally less distractions because, you know, you're just there to do one thing.

01:16:41.000 | And also the emails somehow seem less significant.

01:16:43.240 | Yeah, yeah.

01:16:44.680 | It's just, you can afford to focus on this one thing and it just kind of does something

01:16:52.240 | to you.

01:16:53.240 | It's a little hard to describe, but, you know, if you then fast forward, maybe I can speak

01:16:58.880 | a little bit about that.

01:17:00.560 | I have done a lot of astrophotography there as well, so, and observing faint dwarf galaxy

01:17:06.720 | stars, you know, these are like 45 minutes, 55 minute exposures, so you actually have

01:17:10.840 | a lot of time.

01:17:11.840 | And I would run outside and just lay on the ground under the Southern Milky Way, beautiful,

01:17:18.800 | right up, you know, there.

01:17:21.240 | And I would just lay there like the snow angel, you know, and just stare up there and just

01:17:27.960 | kind of let my thoughts sort of pass through my brain and just like, I'm one of it, right?

01:17:34.880 | We talked about this in the beginning.

01:17:36.980 | This is when I personally have the feeling that I'm a part of it, I belong here, rather

01:17:42.560 | than feeling kind of small.

01:17:44.120 | Yes, I'm small, but there are many other small things and lots of small things make one big

01:17:48.440 | whole, right?

01:17:49.440 | Yeah, we're part of that big whole.

01:17:51.760 | So that's looking at the inner spirals of the Milky Way galaxy.

01:17:56.160 | And just, you know, this dark sky with the bright stars.

01:18:01.160 | And I have described this in my book years ago, if the Milky Way is all bright above

01:18:07.960 | you, you don't need a moon or anything, you can walk in the starlight and you will find

01:18:12.440 | your way.

01:18:13.440 | There are no trees there for safety reasons, but you wouldn't even run into a tree, right?

01:18:18.760 | I mean, you can see, you can almost see the shadow, you know, from the starlight because

01:18:23.440 | it's such a dark sight and the stars are so bright.

01:18:26.880 | And these are kind of moments that kind of change you a little bit.

01:18:32.480 | And you see the unity of it all.

01:18:34.320 | Yeah.

01:18:35.320 | And it's just you and nature and, you know, with modern civilization and all of that,

01:18:42.040 | I think we often try a little bit too hard to be removed from nature, you know, to be

01:18:47.120 | independent of it and figuring it all out.

01:18:50.460 | But at the end of the day, we're just a part of it.

01:18:54.540 | And that really helps me to remember that, you know, we're one in the same.

01:19:00.860 | Well, that fills me with hope that, because I tend to think of us humans as in the very

01:19:05.980 | early days of whatever the heck we are.

01:19:08.300 | And so that makes me think thousands, tens of thousands, hundreds of thousands of years

01:19:13.780 | from now, that we'll be reaching, whatever we become, we'll be traveling out there to

01:19:19.780 | explore more and more and more.

01:19:21.940 | So what you're doing is the early days of exploration with the tools we have.

01:19:26.100 | Yes, the early seafarers looking at the sky for navigation.

01:19:30.820 | Coming up with different theories of what's on the other side, that the earth, starting

01:19:35.100 | to gain an intuition that the earth may be round.

01:19:38.140 | And then we might be able to navigate all the way around to get to the financial benefits

01:19:43.020 | of getting spices from India, whatever the reason, whatever the grant funding process

01:19:48.040 | is all about, but ultimately actually results in a deep understanding of the mystery that's

01:19:53.900 | all around us.

01:19:56.060 | And I mean, it's just to travel out there.

01:19:58.740 | I mean, to me, the discovery of life in the solar system, I really hope to see that in

01:20:07.380 | my lifetime.

01:20:08.380 | Some kind of life, bacteria, something, maybe dead, because that means there's life everywhere.

01:20:15.980 | And that's just the kind of stuff that might be out there.

01:20:22.380 | All the different environmental conditions, chemically speaking, that are out there.

01:20:27.380 | It just seems like when you look at earth, life finds a way to survive, to thrive in

01:20:33.060 | whatever conditions.

01:20:34.740 | And so maybe that process just kind of humbles you and is super exciting to know that there

01:20:41.900 | is life out there of different forms.

01:20:44.700 | Of course, that raises the question of what is life, even?

01:20:49.260 | We tend to have a very human-centric perspective of what is a living organism and what is intelligence

01:20:56.100 | and all this kinds of stuff.

01:20:57.740 | And all the work in artificial intelligence now is starting to challenge our ideas of

01:21:02.100 | what makes human beings special.

01:21:04.820 | I think we're doing that through all kinds of ways, and I think you're working some part

01:21:08.440 | doing that as well.

01:21:10.340 | The unity you feel is realizing we're part of this big mechanism of nature, whatever

01:21:16.620 | that is, that's creating all kinds of cool stuff from the humble, pristine origins to

01:21:22.220 | today.

01:21:23.220 | So if you could just kind of linger on the process of the data, what does the data look

01:21:30.860 | like?

01:21:32.020 | And how does the raw data lead to a discovery of an ancient star?

01:21:40.100 | Well as a spectroscopist, we have to, I guess, talk for a brief moment about what a spectrum

01:21:45.260 | is.

01:21:49.580 | Everyone I hope has seen a rainbow in the sky.

01:21:52.460 | That is basically what we're doing.

01:21:57.020 | We don't send the starlight through a raindrop that then gets bounced around and splits up

01:22:02.340 | the light into the rainbow colors.

01:22:06.380 | We do it with a spectrograph, so basically a prism.

01:22:09.740 | So we send the starlight through a prism of sorts and that splits it up, and then we record

01:22:15.980 | exactly that.

01:22:17.340 | So it's a little 2D picture actually of a spectrum.

01:22:23.500 | Now it's not going to look colorful, just black and white.

01:22:28.700 | Different colors have of course different energies, that's what we record.

01:22:34.220 | More specifically, we record it as wavelengths, so wavelengths and frequency and energies

01:22:40.100 | all the same at the end of the day.

01:22:44.300 | We process that little image in a sense that we do a crosscut and then sum up a few columns

01:22:52.220 | so that we get all the data that we recorded.

01:22:55.700 | And what we see is a, it's a bit funny to describe just with words, but a wiggly line

01:23:02.880 | with lots of dips.

01:23:04.420 | So the 2D processed spectrum, we call it continuum, so it's just a flat line basically and then

01:23:09.740 | there are dips.

01:23:10.740 | So the interesting things are the dips.

01:23:13.200 | If you think back of the rainbow, what we actually see in our stars is not just a rainbow,

01:23:18.620 | but it would be a rainbow with lots of black lines in it, which means certain little pieces

01:23:24.640 | of color have been eaten away by a certain amount.

01:23:29.260 | So we can no longer see it as well or not at all.

01:23:34.340 | Why is that happening?

01:23:35.660 | So if we come back to our stars, what we're observing, we're observing the stellar surface.

01:23:39.680 | We can actually never peer with our telescopes inside, we only ever can go after the surface.

01:23:46.660 | And the surface contains, or the surface layer contains different kinds of elements.

01:23:55.660 | Every one of those types of atoms, so elements are just different types of atoms, they absorb

01:24:02.100 | different photons that are coming from the hot core where the fusion is occurring.

01:24:08.120 | And so that means that if you were the observer, you know, with a spectrograph or without,

01:24:14.180 | you will see the starlight, but certain frequencies, certain energies of that light will have been

01:24:20.300 | absorbed by all the different atoms in the gas.

01:24:23.880 | So you see less of them.

01:24:25.220 | And so those are the dips.

01:24:27.300 | And the strength of the dips tell us which element was it and how much of that element

01:24:37.120 | was or is in the star.

01:24:40.380 | So we have many, many, many dips.

01:24:42.700 | The solar spectrum for reference, all the dips are overlapping because the abundance

01:24:47.940 | of all the elements is so high.

01:24:50.860 | It's actually a very complicated spectrum.

01:24:53.140 | My spectra really look like a straight line and then there's a dip here and then you have

01:24:57.260 | the straight line again, there's a dip there.

01:24:59.020 | The Sun doesn't have straight lines.

01:25:00.260 | I mean, it's just all absorbed in some form or another.

01:25:05.020 | But the old stars have so little of all the elements that there are only occasionally

01:25:10.900 | these dips that then indicate, okay, that one at that wavelength was iron and here we

01:25:15.900 | have carbon and there's magnesium and sodium and there's a little strontium line here.

01:25:21.180 | So we have a much easier way to map out this barcode that the spectrum pretty much is at

01:25:29.780 | the end of the day and to then measure the strength of these, we call it absorption lines,

01:25:36.060 | to then calculate with existing codes that mimic the physics of the stellar atmospheres,

01:25:41.100 | like how much was absorbed, what kind of elements were present in the stellar atmosphere.

01:25:48.580 | And so this is how we get to our abundance measurements and then all together that gives

01:25:53.020 | us the chemical composition and that particular signature in that star.

01:25:59.020 | - If you ever look at like the raw spectrograph and the absorption line and are able to see

01:26:06.220 | into it some interesting non-standard outlier kind of patterns or does this have to do heavy

01:26:14.860 | amount of processing?

01:26:18.120 | - We actually process, it's fairly straightforward to do our processing.

01:26:23.960 | We do it at the telescope.

01:26:25.420 | So I often take a shorter exposure first, let's say 10 or 15 minutes.

01:26:31.820 | So mostly when I do discovery work, we just take a quick look spectrum, then we process

01:26:37.260 | it while we observe the next star.

01:26:39.920 | Then we take a quick look, we have what I call the summary plot.

01:26:43.700 | It's a collection of little areas in the spectrum that have the key positions, the positions

01:26:50.740 | of the key elements in it.

01:26:52.500 | And it's kind of like reading the tea leaves.

01:26:55.140 | I have stared at so many spectra, I just need to know, I just need to see our summary plot

01:27:00.380 | and I can tell you exactly what the numbers are going to be.

01:27:03.300 | - And also to tell if it's going to be promising to look at further?

01:27:06.900 | - Yes, exactly.

01:27:07.900 | And so that's it.

01:27:08.900 | Thumbs up, thumbs down.

01:27:10.860 | Are you worth my time or not?

01:27:13.780 | In most cases it's not, or it's good enough, we can do a basic analysis, maybe publish

01:27:18.380 | this as part of a larger sample just so we output that we have observed the star and

01:27:23.740 | their basic nature, that's an important part to publish as well.

01:27:28.820 | And yeah, I had a run.

01:27:30.980 | So now we do remote observing.

01:27:32.460 | I do all of this now from my home, from my living room all night long.

01:27:40.140 | And I often work with colleagues, so we do it over Zoom and we process the data, we look

01:27:46.660 | at it, same thing still.

01:27:48.580 | And we just found a star that had a very low iron abundance.

01:27:54.300 | And then we decided, okay, that looks interesting, we're just going to keep exposing.

01:27:58.740 | So we took more data on it on the spot and we're writing up the paper right now.

01:28:03.100 | - How do you know where to point the telescope?

01:28:05.180 | - It's not random.

01:28:07.180 | There's a lot of work that goes into that.

01:28:11.140 | I began my career by trying to answer that question as in like doing the search process.

01:28:19.740 | That's why I called my book that I've written some time ago, "Searching for the Oldest Stars"

01:28:25.820 | because searching is one thing, it's very time consuming.

01:28:29.780 | And then on top of that, not everyone finds, right?

01:28:32.060 | And I often don't find, but I keep searching because techniques have established that yes,

01:28:38.980 | we can do it if we're just patient enough and keep going because it's a numbers game.

01:28:44.620 | And that's often the case in science.

01:28:47.420 | And that's something that not enough is talked about, how tedious it is and how long it takes

01:28:54.900 | to get to that one discovery, right?

01:28:59.860 | That moves the field further.

01:29:01.260 | - And how difficult it is to believe that there's a thing to be discovered.

01:29:06.620 | - Yes, yes.

01:29:08.820 | We have the saying, I learned this I think from my supervisor, one star is a discovery,

01:29:15.540 | two is a sample and three is a population.

01:29:20.420 | So as soon as you found three of roughly the same kind, you're done.

01:29:25.300 | But you need to get there.

01:29:26.620 | - Yeah, probably the first is the hardest, right?

01:29:29.580 | - Yes.

01:29:30.580 | - It kind of remains really hard.

01:29:33.860 | But the thing is then at past three, many of us are like, okay, we solved that problem.

01:29:38.540 | We've done it three times, we can do it.

01:29:42.020 | That's a thing, right?

01:29:43.020 | That's a population, three iron deficient stars, let's say, right?

01:29:47.820 | That's one puzzle piece.

01:29:48.940 | Now we can move on to the next thing.

01:29:50.660 | - That's an indicator that there's many more of them potentially.

01:29:53.340 | - Yes, yes, yes.

01:29:54.500 | So to cut a long story short about the searching, we started early on with what's called low

01:30:01.700 | resolution spectroscopy of many stars.

01:30:04.180 | So for example, my thesis work almost 20 years ago was piggybacking off a quasar survey that

01:30:12.100 | had collected, so quasars are basically giant supermassive black holes that are really far

01:30:18.300 | away.

01:30:19.300 | So you only see one big bright light point.

01:30:21.820 | So it looks like a star, but it's actually just a giant supermassive black hole that

01:30:25.740 | outshines its own galaxy.

01:30:29.460 | And people had been trying to study those and they had taken little spectra of all things

01:30:36.180 | in the sky and it turns out, oh, you can fish out the actual stars from that and look for

01:30:41.300 | certain signatures that might indicate low metallicity stars, so stars with low abundances.

01:30:50.060 | And so it was painstaking work to then take medium resolution spectroscopy to get a little

01:30:55.860 | bit more information and to use approximations and to kind of get candidates that we can

01:31:00.260 | then eventually take to the big glass like Magellan to get a high resolution spectrum.

01:31:05.460 | So we really see the dips of all the individual elements that then give us the final answer,

01:31:10.700 | is it yay or nay?

01:31:13.620 | These days with another grad student I developed a new technique to use images actually of

01:31:22.420 | all the stars in the sky taken with very narrow filters.

01:31:26.700 | So it's like you're wearing very specific glasses that only let so much light through.

01:31:31.680 | And so we can do similar things through having several narrow band filters, what we call

01:31:38.100 | it, to fish out things that have no absorption over here, so just the straight line and then

01:31:45.180 | a little dip here, so a little something there.

01:31:49.620 | And that has proven fairly successful in recent years.

01:31:53.180 | - So looking at the entire, looking at broader regions of space.

01:31:57.740 | - That's right, because these stars are a little bit like the needle in the haystack,

01:32:01.100 | right?

01:32:02.100 | There are not that many left over and certainly the galaxy has made plenty of stars in between.

01:32:07.420 | We need to comb through all of those to get to the goods.

01:32:12.660 | So we always start with millions and then work our way down and in the end we have like

01:32:16.820 | three good candidates.

01:32:17.820 | - I wonder how those ancient stars feel that they were noticed.

01:32:22.180 | They probably know that nobody pays attention.

01:32:24.380 | No, I'm just kidding.

01:32:25.700 | - We're all special, right?

01:32:27.380 | So are the stars.

01:32:28.380 | - It's good, it's inspiring, even if you're the outcast.

01:32:33.420 | In your pristine nature you still might nevertheless be noticed.

01:32:36.740 | I'm hoping the same about humans if somebody's observing us.

01:32:42.420 | Is there something else you could say that's about the challenges of this kind of high

01:32:46.580 | precision measurement that you're doing?

01:32:50.460 | So this kind of collection of data looking, trying to kind of pull out the signal from

01:32:58.140 | the noise out there.

01:33:00.860 | - Well that's literally what we're doing in multiple ways actually.

01:33:04.860 | We're trying to find the needle in the haystack and then we find something and then it turns

01:33:09.580 | out it's just a little bit too faint to actually get the kind of data quality on it that we

01:33:14.740 | would like or that would be warranted given the potential of the star, right?

01:33:21.060 | It's like, "Ugh!"

01:33:22.420 | - So there's always noise.

01:33:24.420 | There's always a little bit of noise and you have to try to say like, "How special is this

01:33:29.180 | when you're looking at the absorption line?"

01:33:32.100 | So the most iron-poor stars, their iron lines are so tiny that they're literally almost

01:33:37.980 | in the noise.

01:33:38.980 | So you need incredibly good data to make detections.

01:33:45.300 | And the funny thing is we're looking for the nothingness of, let's say, the iron lines,

01:33:50.820 | but then we don't want nothing because if there's nothing in the spectrum we can't measure

01:33:54.780 | anything.

01:33:55.780 | We can only get an upper limit.

01:33:57.540 | But we'd really like a measurement.

01:33:59.220 | So we are looking for the last little bit that you could possibly detect.

01:34:03.200 | And that's a strong function of the brightness of the star because the telescopes have the

01:34:07.220 | size that they do.

01:34:09.460 | That's not going to change for a while.

01:34:10.820 | Hopefully eventually it will, but it's going to be at least 10 years out.

01:34:15.000 | And so yes, we're often literally stuck in the noise because we can't make the measurements.

01:34:19.980 | So actually the record holder for the most iron-poor star only has an upper limit.

01:34:24.500 | We can't get enough data on this to actually pinpoint a measurement to then take it to

01:34:28.700 | our theory colleagues and say, "Give me this little iron out of your first star."

01:34:34.500 | So it's a bit frustrating, but also super exciting at the same time.

01:34:38.020 | - So let's go to both sides of that spectrum.

01:34:40.700 | What's the most exciting discovery to you personally?

01:34:46.060 | Is there a moment you remember that you saw a piece of data and your heart skipped a bit?

01:34:52.700 | - Yeah, yeah, of course.

01:34:56.620 | - Is it HE 1327?

01:34:59.500 | - That was definitely one of those moments.

01:35:01.740 | I wasn't actually present at the telescope, but we were sent the data immediately from

01:35:05.180 | our colleague.

01:35:07.140 | And we just looked at it and our eyes got really wide and it was like, "Oh my God, this

01:35:13.100 | is really what you think it is?"

01:35:15.260 | So we had to run some numbers and it was.

01:35:18.660 | And these are magical little moments.

01:35:22.620 | The thing is, often we have false positives.

01:35:28.380 | And so there's always this kind of period.

01:35:31.220 | And often it's, I don't know, 10, 15 minutes where you need to make some tests to kind

01:35:36.260 | of make the decision, "Is this really something I should keep observing now?

01:35:39.260 | Is this really as good as I think?

01:35:40.980 | Or am I being fooled by something?"

01:35:42.860 | So actually, if you take a spectrum of a white dwarf, a white dwarf is the leftover core

01:35:48.580 | of a star like the Sun that has gone extinct.

01:35:53.740 | And white dwarfs have lost all their outer atmosphere, so it's just the hydrogen-helium

01:35:57.500 | core, so they look like a metal-poor star because that's the only hydrogen-helium left,

01:36:02.180 | right?

01:36:03.180 | But the hydrogen lines that you can see in the spectrum of our stars and of the white

01:36:07.060 | dwarfs are a little bit wider than normal.

01:36:10.260 | So you need to have a good eye just to check, "Does this look a little bit wider than us?

01:36:15.900 | Is this a white dwarf who's fooling me here?"

01:36:18.300 | And so it's like this moment, it's like, "Oh my God!"

01:36:22.060 | - It's just minutes of nervousness.

01:36:23.980 | - Yes, yes.

01:36:25.060 | And sometimes it's a dud and sometimes it's not.

01:36:30.340 | - What's been a big, that you remember, heartbreak?

01:36:32.900 | Like a painful low point?

01:36:34.980 | Is it all leading up to the first...

01:36:37.500 | Is it all about HE 1327 again?

01:36:40.020 | Just the leading up to it?

01:36:41.020 | Or has there been like a...

01:36:42.020 | Yeah, has there been like low points in this search?

01:36:47.300 | - That's a good question.

01:36:49.860 | I mean, you know, it starts with mundane things as in like, you won your telescope time, you

01:36:55.780 | traveled there, and the weather is completely cloudy, it rains, and you had three nights,

01:37:02.940 | which is a lot, and you go home empty-handed.

01:37:06.380 | So that's definitely a low point.

01:37:09.820 | Probably not what you were thinking of, but there is a certain occupational hazard to

01:37:13.940 | it.

01:37:14.940 | - Yeah, it requires a kind of resilience and a patience.

01:37:18.460 | - Yeah, and you just gotta learn to live with it.

01:37:21.940 | Coming back to Reticulum 2, actually, you know, that little dwarf galaxy, that was a

01:37:25.740 | run that we had, and the weather was incredibly bad.

01:37:29.740 | And I had sent my student there, and I was at home, and he calls me at 2 a.m., and he

01:37:36.980 | was like, "Anna, I think I observed the wrong star, I'm so sorry."

01:37:41.180 | There is this line there, this Europium line, and it looks like a metal-rich star.

01:37:46.260 | And I was like, "It's cool, we all make mistakes.

01:37:50.940 | Send me the data, send me that summary plot."

01:37:53.980 | And so I look at it, you know, I was like super tired.

01:37:57.020 | It's like, I can't really tell, it doesn't look wrong, but I can't tell you right now

01:38:04.180 | that it's right either, so why don't you go to the next target?

01:38:09.020 | And he calls me back an hour later, "Anna, it looks just the same!

01:38:13.900 | What am I supposed to do?"

01:38:16.680 | And then I joked, "Well, maybe we found an R-process galaxy.

01:38:19.940 | Let's go to the next one!"

01:38:23.100 | And the weather was degrading.

01:38:26.460 | And so to cut a long story short, we had to come -- so he was observing the right stars.

01:38:32.820 | It was an R-process galaxy, the first one we had ever discovered, totally unpredicted.

01:38:41.700 | We had no idea that this was a thing.

01:38:46.620 | Of course we thought that such a thing might possibly exist, because why not?

01:38:53.740 | Neutron star mergers happen somewhere, crazy supernovae probably too, but we were not prepared

01:39:01.020 | in that moment to find this thing.

01:39:04.940 | And in the end, the weather was getting worse and worse, and we wanted to see how many R-process

01:39:12.180 | stars are in this galaxy.

01:39:14.060 | So we managed by a hairline to observe the nine brightest stars, but the data quality

01:39:20.820 | was atrocious.

01:39:21.820 | And the weather affects the data quality.

01:39:23.780 | Yes, absolutely, because these were really faint stars.

01:39:27.220 | And so we were really lucky by making a very tight strategy of getting the absolute bare

01:39:35.660 | minimum for all the stars so we could at least take a very crude look, "Is it a yay or is

01:39:41.580 | it a nay?"

01:39:42.580 | We couldn't even say yes or no, just to get an idea, because we needed to know.

01:39:47.940 | Why was that important?

01:39:49.180 | Because we could only observe this system again nine months later.

01:39:54.220 | So there's always a window of observation.

01:39:56.020 | Yes.

01:39:57.020 | So we were betting this was our chance, and it was going away with the clouds.

01:40:04.420 | That was super high stakes.

01:40:06.020 | But we just made it.

01:40:09.060 | Really, it was almost impossible.

01:40:12.380 | And the thing is, this is such a serendipitous moment.

01:40:18.780 | In a serendipitous moment, the enhancement of these heavy elements was so strong that

01:40:24.060 | even in this really crappy data, we could still see the enhancement.

01:40:29.700 | The absorption was so strong that it stuck out of the noise.

01:40:32.660 | If that enhancement wouldn't have been as strong, we would not have been able to say

01:40:36.820 | anything because we wouldn't have been able to tell.

01:40:40.440 | But because it was so extreme, it lent us a hand, despite the weather and all, to say

01:40:46.300 | like, "Yes, this is it."

01:40:48.940 | So that was quite the night.

01:40:51.460 | Luck, I mean, a lot of this is just luck.

01:40:55.940 | So that was the first our process galaxy discovered.

01:40:58.140 | Yes.

01:40:59.140 | I didn't sleep all that much.

01:41:01.140 | Do you have hope?

01:41:03.740 | Are you excited about James Webb Space Telescope and other telescopes in the future that increase

01:41:10.180 | the resolution and the precision of what can be detected out there?

01:41:14.660 | Absolutely.

01:41:15.660 | JWST is fantastic already.

01:41:17.700 | I am not planning to use it personally, although I think I'm on one or two observing proposals

01:41:23.180 | actually, because similar to what we already spoke about, we're interested in the same

01:41:28.540 | thing.

01:41:29.540 | We're just kind of looking at a different sides of the fence.

01:41:32.500 | I have my old surviving stars and I concoct these little stories about what the earliest

01:41:37.860 | galaxies may have looked like, what the objects were that contributed energy and elements

01:41:43.860 | and all these things.

01:41:45.700 | And my JWST colleagues, they try to detect some of these earliest photons from these

01:41:51.300 | earliest systems to look at the energetics and other things.

01:41:56.620 | What was there?

01:41:57.620 | How many?

01:41:58.620 | These kinds of things.

01:41:59.620 | So together we're trying to explore this first billion years, but we do it in very complementary

01:42:06.220 | ways.

01:42:07.220 | And so I'm very excited to see what they can come up with and how that helps me to inform

01:42:13.780 | my stories better and more comprehensively.

01:42:17.660 | What do you think is the future of the field of stellar archaeology?

01:42:22.980 | How much can we, maybe what are the limits of our understanding of this first billion

01:42:27.860 | years of our universe?

01:42:29.620 | Well, obviously lots of limitations in the sense that I always say, I have a metal pore

01:42:36.460 | star for any of your questions, because there are so many different kinds out there.

01:42:43.020 | And we still find new patterns sometimes, right?

01:42:45.460 | And there needs to be an explanation.

01:42:46.820 | The question is, is it ultimately just one quirky star?

01:42:49.740 | Is it two or is it three, right?

01:42:51.540 | Is it a sample?

01:42:52.540 | Is it a population?

01:42:53.540 | So we haven't concluded that kind of work yet.

01:42:56.140 | So every metal pore star is a kind of data point that you can use to improve the quality

01:43:01.660 | of your model of how the evolution of the early universe.

01:43:05.020 | Yes, yes.

01:43:06.020 | And I would say we've made huge progress over the last 20 years.

01:43:11.260 | When I joined that field, it was in its infancy, and there was this serendipitous discovery

01:43:15.780 | of that first, second generation star.

01:43:19.100 | And we have filled in the canvas a great deal since then.

01:43:23.700 | And this is what I have greatly enjoyed about doing so, because there was so much discovery

01:43:29.340 | potential.

01:43:30.860 | And it's been dying down a little bit because of all the progress.

01:43:36.980 | It's on the up and coming again because there are so many large spectroscopic surveys in

01:43:43.820 | the works now that will just provide a different level of data that we haven't had before.

01:43:49.020 | I'm sort of of this older generation.

01:43:52.140 | I have only very few colleagues.

01:43:53.820 | I work in small teams, and I observe every single star myself.

01:43:59.900 | Whatever I can, I do myself.

01:44:01.540 | I don't generally take other people's data, at least not certainly not in the end stage.

01:44:09.020 | And I'm not a big data kind of person, although we're all headed that way.

01:44:14.740 | I certainly use data from the Gaia astrometric satellite for the kinematics, for example.

01:44:22.580 | But that's personally a new thing for me to use sort of big sky surveys that are available.

01:44:29.000 | So it's still very sort of hand-grown field where we do our individual observations.

01:44:35.740 | I have enjoyed that a lot, but that's about to change.

01:44:39.460 | - So one star at a time.

01:44:40.460 | - Yes.

01:44:41.460 | - I mean, there's power to that, to build up intuition of the early universe by looking

01:44:44.900 | one star at a time.

01:44:47.060 | - And this is how you can really drill down on the questions that you have, right?

01:44:50.740 | Because you control what data you get.

01:44:54.380 | Otherwise you have the data that you have, right?

01:44:56.820 | You get what you get and you don't get upset.

01:45:00.040 | I don't like that.

01:45:01.040 | I'm a little bit snobby.

01:45:02.820 | I really like to formulate my questions, go to the telescope and then come what may, I

01:45:07.920 | will try to get it.

01:45:09.060 | - And also develop the intuition of where the data can be relied upon and where it can't

01:45:13.220 | and all the different quirks of the data and all that kind of stuff.

01:45:16.100 | Sometimes a lot is lost in the aggregation of the noisy data.

01:45:20.700 | - Yeah, yeah, yeah.

01:45:22.460 | And that's always the danger if you have someone else's data that you just don't really understand

01:45:26.180 | the limitations, completeness things, how certain things were set up and you get out

01:45:34.260 | what you put in.

01:45:35.460 | So I'm really particular about that and it certainly paid off for me.

01:45:39.780 | That's one of the main notions that I try to teach in my classes and to my students

01:45:45.580 | that you need to be able to formulate your question really well because otherwise you're

01:45:50.860 | going to get an answer to a different question, but you won't notice that the goalpost has

01:45:56.500 | shifted in the meantime, right?

01:45:58.620 | So your interpretation can only be as good as the question.

01:46:01.620 | If you need to change your question, that's cool.

01:46:04.140 | Do it.

01:46:06.420 | But then it needs to pair up with your interpretation again.

01:46:09.460 | And so knowing, really being in the know about every step of what happens, that leads to

01:46:15.980 | quality results, I think.

01:46:17.860 | So I have sometimes a little trouble with sort of big data and statistical analysis.

01:46:22.260 | Yes, on average, that's true.

01:46:24.860 | I'm not debating that, but I'm the kind of person I like to look at the outliers, so

01:46:30.100 | not the bulk, but the special ones.

01:46:34.180 | And they just need to be treated in a different way and there needs to be an acknowledgement

01:46:37.500 | of that, different ways for different things.

01:46:40.180 | - So big data can look at divorce rates and perhaps you and I are more interested in the

01:46:46.460 | individual love stories.

01:46:48.220 | - Yes.

01:46:49.220 | (laughing)

01:46:50.220 | That works for me.

01:46:51.900 | - So I don't know if it's possible to say, but what do you think is the big discoveries

01:46:57.260 | that are waiting?

01:46:59.560 | Is it on the different dynamics of the yield, the common narrative, the common story of

01:47:06.100 | how some of these metal poor stars are formed?

01:47:11.220 | Where are the discoveries in this field that you think will come?

01:47:14.940 | - I think the individual discoveries are actually, we've made most of those, certainly through

01:47:22.460 | individual stars.

01:47:26.420 | Finding yet another second generation star is incredibly important for me, but isn't

01:47:31.340 | really going to move the needle.

01:47:33.940 | Finding 50 of them or 100 of them, that would move the needle, but that's in a word or two

01:47:38.580 | magnitudes up.

01:47:41.100 | And new search techniques and new surveys may enable that, but would you still call

01:47:48.100 | that a discovery?

01:47:49.100 | - Sure.

01:47:50.100 | - Right?

01:47:51.100 | - So that's just a scale, that's a scale.

01:47:52.460 | - Yes.

01:47:53.460 | So I think about it more like literally of the puzzle.

01:47:56.700 | Let's say you have a thousand piece puzzle and you have 900 pieces in there.

01:48:02.220 | If you're a person like me, I want to get to the last ones.

01:48:05.620 | I'm not going to leave it just like, okay, I see broadly what this is going to look like,

01:48:09.420 | right?

01:48:10.420 | I'm going to have, no, I want to get to the last one.

01:48:14.180 | Is the picture globally going to change?

01:48:17.100 | No.

01:48:18.100 | Are we going to figure out all the details and how it really works?

01:48:21.660 | Yes.

01:48:22.660 | - So really careful, detailed map out the ancient stars of our universe.

01:48:30.300 | - Yeah, because I think that's what many of us scientists are a little bit detail obsessed,

01:48:36.580 | but I think that's our job too, right?

01:48:38.660 | To really kind of make it airtight, to really walk away saying, I fully understand this,

01:48:45.780 | not just broadly, but I really know, we really know now.

01:48:51.300 | And so more and more of that is going to happen.

01:48:56.020 | And so I think this is probably true across astronomy.

01:48:58.740 | These individual 10 sigma discoveries become less and less.

01:49:04.600 | If they were easy, we would have made them already, right?

01:49:07.580 | Which means we have made many of them.

01:49:11.380 | But really filling in the details is the next sort of level of discovery.

01:49:17.700 | Maybe we need to find a new word for that.

01:49:21.820 | The hopes and expectations that go along with the word discovery are so enormous.

01:49:27.460 | We may not always be able to live up to that, but it doesn't mean that we're not finding

01:49:32.860 | out new things.

01:49:34.260 | It's just a different kind of quality because the questions have shifted.

01:49:38.220 | You close one door, suddenly there are 10 new open doors that we want to explore and

01:49:43.100 | march through.

01:49:44.820 | And that's finding these last puzzle pieces here and there that really make it airtight.

01:49:50.100 | - So there's a lot of value and a lot of power and beauty to the discovery in the big picture

01:49:56.340 | of our universe and in the details.

01:49:58.540 | - Yes.

01:49:59.540 | - So both are really important.

01:50:00.540 | - We need both, absolutely.

01:50:03.740 | - Drifting into the philosophical, let me ask about the Big Bang as we kind of encroach

01:50:10.340 | onto it.

01:50:11.340 | So your work is kind of taking steps back through time in a weird way.

01:50:16.700 | Do you think we'll get to deeper and deeper understand the really, really early days of

01:50:23.540 | the Big Bang?

01:50:25.260 | And the philosophical question, do you think we'll be able to understand what was before

01:50:29.700 | the Big Bang or why the Big Bang happened?

01:50:32.500 | Do you think about that stuff?

01:50:35.380 | - Not with stars, for better or for worse, because stars only probe the time when they

01:50:41.460 | were formed and the Big Bang is surely before then.

01:50:45.940 | I mean, I often talk to my students about the difference between math and physics.

01:50:51.220 | Let me give you an example.

01:50:53.300 | We talked earlier about 1815-23 and I was happy to share with you that I measure thorium

01:50:58.700 | and uranium, but I actually didn't quite close that loop.

01:51:01.660 | So we did this to try to attempt to calculate an age for these stars, right?

01:51:09.020 | But they rely on us knowing how the R process works, how these elements are created, where

01:51:15.620 | it happens, and then how those elements get dispersed into the gas and end up in the next

01:51:21.140 | generation star.

01:51:22.140 | So quite a few question marks.

01:51:24.700 | So that's how we got to the age of 13.2 billion years.

01:51:28.740 | This is probably not accurate, but this is the best calculation we could do.

01:51:36.340 | The reason why I'm bringing this up is that that was actually the average of multiple

01:51:41.140 | elemental ratios that each gave a certain age and then we averaged that because for

01:51:45.820 | better or for worse, this is the best we can do.

01:51:48.260 | So some of these numbers said, "Oh, this star is 15 billion years old."

01:51:54.060 | And then others said, "Oh, this is 10 billion years old."

01:51:56.540 | And so I often use that in my class to say, "What's the good news and what's the bad

01:52:02.780 | news here?"

01:52:04.580 | Some ratios say 15, some say 10, right?

01:52:07.660 | Is 15 correct?

01:52:11.140 | And then I ask them and some people will say something.

01:52:14.580 | And so the thing here is that it's an absolutely correct calculation given the mathematical

01:52:20.780 | and physical model that we constructed.

01:52:23.520 | But does it make sense?

01:52:24.860 | No, it doesn't.

01:52:26.380 | If we believe the universe is 13.8 billion years old, 15 is ridiculous, yet it is correct.

01:52:34.020 | Isn't that interesting?

01:52:35.440 | Correct from a mathematics perspective.

01:52:36.660 | Yes, it is not incorrect because this is what I calculated.

01:52:39.860 | Nobody made a mistake.

01:52:41.140 | Now we can question whether that's a good model, but that's a separate issue.

01:52:45.620 | So you're saying physicists are much closer to truth than mathematicians.

01:52:49.220 | Well, it depends.

01:52:52.300 | Sometimes yes and sometimes no, right?

01:52:53.860 | So what our job as physicists is, is to take the mathematical model, calculate our numbers,

01:53:00.140 | and then ask the question, "Does this make sense?"

01:53:03.940 | Now in the case of 15, it doesn't, but we took the average anyway because that was the

01:53:11.860 | best we could do.

01:53:13.500 | So all right, let's put that aside.

01:53:15.320 | Let's apply the same sort of thinking to the Big Bang.

01:53:18.540 | Math can tell us things that we as physicists cannot grasp because it doesn't make sense

01:53:23.300 | to us.

01:53:24.300 | Now in the case of the Big Bang, that's a special case because we don't actually know

01:53:29.380 | what's supposed to make sense.

01:53:32.300 | And this is where things get interesting, but this is where math will ultimately be

01:53:35.620 | the winner because we can no longer say, "This makes sense," or, "This doesn't make sense,"

01:53:40.940 | because the physics is broken down.

01:53:42.980 | But math breaks down too in the singularity of things.

01:53:46.180 | Well, depending on who you ask.

01:53:48.900 | Okay, sure, sure.

01:53:51.260 | This is the current question, right?

01:53:53.300 | How far, how much further can we push math, let's say, to the front of the Big Bang, if

01:53:58.740 | there is such a thing?

01:54:00.860 | What's the front and the back?

01:54:01.860 | What's the front?

01:54:02.860 | The front is the...

01:54:03.860 | Before the Big Bang.

01:54:04.860 | Oh, before the Big Bang.

01:54:05.860 | The front, okay.

01:54:06.860 | Just to clarify, all the doorways and the entrances.

01:54:11.220 | So how far can we let the math go before that stops to make sense, right?

01:54:17.380 | And I don't know what the answer is to that, but it's really cool that because math is

01:54:22.180 | not limited by our physical nature, it can probably go a little bit further than the

01:54:28.060 | physics.

01:54:29.060 | Yeah.

01:54:30.060 | Right?

01:54:31.060 | And math can go into more dimensions than four dimensions comfortably.

01:54:34.820 | And it's judgment-free because it just calculates things on its own.

01:54:39.180 | As physicists, we are so judgmental.

01:54:41.940 | This makes sense, this doesn't make sense, right?

01:54:44.380 | It doesn't get any worse.

01:54:45.860 | That's such a beautiful dance.

01:54:49.540 | It's so amazing that through this dance, you can explore the origins of the universe.

01:54:56.260 | Doesn't the Big Bang just blow your mind?

01:55:00.460 | This thing has just started from a point.

01:55:02.340 | Yeah.

01:55:03.340 | And now we're here.

01:55:04.340 | Yeah, yeah, yeah.

01:55:05.340 | Hydrogen and helium.

01:55:06.340 | And then all the stuff you're studying, I mean, this evolution of chemistry created

01:55:14.140 | humans, and we're here talking.

01:55:18.660 | And there's a lot more to the story.

01:55:21.580 | It's amazing.

01:55:22.580 | Yeah, yeah, yeah.

01:55:25.980 | And this kind of march that you're doing is observing data.

01:55:31.660 | Is there...

01:55:34.180 | You're looking at old light and old data.

01:55:37.920 | But only a few thousand years, right?

01:55:39.420 | Just a few thousand years.

01:55:40.620 | That's the difference between me and my JWT colleagues.

01:55:44.100 | Their objects, that light has traveled 13 billion years or whatever it was to us, and

01:55:49.660 | they're observing that now.

01:55:51.340 | My light has only traveled a few thousand years.

01:55:54.740 | It's nothing.

01:55:55.740 | So whatever you observe now is likely still going on.

01:55:58.540 | Yes.

01:55:59.540 | These stars are alive and kicking and having a blast.

01:56:03.700 | Thousand years.

01:56:05.060 | Just a few thousand years, that's all it takes.

01:56:06.700 | If we can travel close to the speed of light, maybe we can reach out there.

01:56:12.140 | We wouldn't have any planets around those stars, though.

01:56:14.860 | So that's...

01:56:15.860 | Is that a definitive intuition?

01:56:17.540 | Well, what are planets made of?

01:56:20.180 | Elements, right?

01:56:21.180 | To take the Earth, all heavy elements, right?

01:56:23.700 | The universe needed to reach a certain stage first to have produced enough of all these

01:56:29.460 | elements to actually make a planet.

01:56:32.260 | So on average, you're...

01:56:33.260 | So, okay, right.

01:56:34.260 | So that took quite a few billion years.

01:56:35.260 | So they're not going to have a mechanism for forming planets.

01:56:38.140 | You could have visitors probably, but the kinematics of that are unlikely.

01:56:42.900 | Yeah, I would say so.

01:56:47.340 | So they're interesting in that they reveal the early chemical evolution of the universe.

01:56:52.660 | Not that they're...

01:56:53.660 | They could be good vacation spots, but not...

01:56:56.100 | Well, if you like the warm.

01:56:59.540 | There's no planet islands to go to, to chill.

01:57:05.580 | In your book, you highlight the major contributions in the field by many women.

01:57:11.940 | Some of these women were not, as you describe, immediately credited for their discoveries.

01:57:18.820 | So for me, from a computer science perspective, the story also tells Harvard computers.

01:57:25.140 | Who were these women and what can you just say about the nature of science and humanity?

01:57:30.940 | Discovering things is part of the human nature, right?

01:57:34.260 | And so it has happened for the longest time, not just by men, but also by many women.

01:57:42.620 | The field of stellar astronomy, which is my field, has particularly benefited from many

01:57:50.660 | discoveries made by women.

01:57:51.920 | You mentioned the Harvard computers.

01:57:54.180 | That's a term used for women who worked about 100 years ago at the Harvard College Observatory,

01:58:04.260 | and they were hired for their low wages and willingness to do diligent and patient work

01:58:11.640 | to comb through the big data of the day.

01:58:16.260 | So the observatory director, they were carrying out large sky surveys at the time, and they

01:58:23.700 | needed -- that data needed to be processed and looked at and analyzed.

01:58:30.500 | And so many women, or several dozens, one or two dozen women over the years, were hired

01:58:40.420 | to do this work.

01:58:42.060 | And in the process, because they were looking at the actual data and they were smart, even

01:58:47.500 | though they had often no formal education, they made a lot of discoveries simply by being

01:58:54.300 | in tune with what they were doing.

01:58:56.700 | So they weren't robots, as the term "computer" would perhaps lead on.

01:59:04.380 | So Annie Jump Cannon classified thousands and thousands of spectra and found out that

01:59:14.620 | you can -- stars have different temperatures and their spectra look according.

01:59:19.900 | We still use that classification sequence today.

01:59:25.180 | Cecilia Payne-Gaposchkin later on, in I think 1925, was one of the first women to obtain

01:59:32.100 | a PhD in stellar astronomy, and she figured out, she calculated, that the Sun is mostly

01:59:42.540 | made of hydrogen and helium.

01:59:45.980 | That seems normal to many of us these days, but at the time, it was thought that celestial

01:59:53.060 | objects are made of the same thing as the Earth.

01:59:56.220 | That's a gutsy, amazing discovery.

02:00:01.020 | Yes.

02:00:02.020 | It was later termed the most important thesis of humankind or something like that.

02:00:09.940 | What a revelation to realize that stars are made of hydrogen and helium, right?

02:00:15.420 | This was exactly the time when people figured out why stars are shining, namely because

02:00:19.540 | of nuclear fusion and that it's protons and the tunneling effect that leads to the actual

02:00:25.220 | fusion.

02:00:26.220 | Otherwise, the protons repulse each other, they don't come together.

02:00:31.700 | And so what an incredible time it was back then.

02:00:34.660 | And so stars and nuclear physics were very closely related, and it remains.

02:00:40.540 | Now it's called nuclear astrophysics.

02:00:43.460 | And so many women had many contributions to that.

02:00:46.500 | Of course, prior to that, Marie Curie discovered two new elements.

02:00:51.460 | Ah, so awesome!

02:00:56.580 | Radium and polonium.

02:00:59.900 | Lisa Meitner discovered nuclear fission.

02:01:03.600 | That is the basis for understanding the R process.

02:01:06.820 | This is exactly what happens in the R process.

02:01:12.020 | The heavy nuclei, let's say uranium, if you bombard it with a neutron, we talked at length

02:01:18.500 | about it, it will decay.

02:01:20.220 | It will split into barium and krypton, let's say.

02:01:27.020 | So two lighter elements.

02:01:28.900 | That's exactly what we observe.

02:01:30.260 | I have always a higher abundance of barium than the heavier elements because of this

02:01:34.180 | fission cycling that she calculated in 1938, 1939.

02:01:42.480 | So many, many contributions, and it's just so remarkable.

02:01:47.300 | If you just take that body of work, that changed how we do things, how we see the universe,

02:01:56.000 | how we understand things has led to so many subsequent discoveries, good ones and bad.

02:02:03.120 | Well, all of it is taken together.

02:02:07.680 | That's progress.

02:02:08.680 | Right.

02:02:09.680 | Science is what it is.

02:02:11.560 | We have to decide what we do with that knowledge, right?

02:02:13.880 | We can always use things for good or for bad.

02:02:17.960 | That's part of the human endeavor as well.

02:02:21.160 | And also part of the human endeavor and the human nature is the issues with corruption

02:02:25.880 | and credit assignment and all these kinds of things that make this whole ride so damn

02:02:30.120 | interesting about what's right and wrong and about the nature of good and evil.

02:02:35.400 | And that seems to surface itself in all kinds of places all the time.

02:02:39.560 | Yes.

02:02:40.560 | Lisa Meitner was nominated for the Nobel Prize 40 times.

02:02:44.120 | More than that even.

02:02:45.200 | It's amazing.

02:02:46.200 | She holds the record for that.

02:02:47.740 | She never received it.

02:02:49.660 | So, case in point.

02:02:53.340 | Yeah, and of course the Nobel Prize has its complexities.

02:02:58.660 | One is the credit assignment, but two, even in astronomy, sort of assigning credit to

02:03:03.340 | a handful of folks when so many more contributed is a complicated story also.

02:03:08.300 | Yes, very complex.

02:03:10.060 | Okay, sorry for the romantic question, but what to use the most beautiful idea in astronomy,

02:03:16.340 | in stellar astronomy?

02:03:18.500 | Well, so early on, when I was in high school, I was thinking like, "Okay, what do I want

02:03:25.780 | to do when I grow up?"

02:03:28.460 | I knew I wanted to do astronomy, but I was a little bit torn because my interests were

02:03:32.900 | definitely stars, stellar astronomy, but also chemistry.

02:03:36.980 | I always had a fascination about the elements, so Marie Curie was a big role model.

02:03:43.720 | My friend actually produced a beautiful movie about the discovery of the elements.

02:03:52.100 | This is a theater play, but digitized, where when I saw it, I could actually kind of relive

02:04:00.520 | the sort of discovery moment that Marie Curie had.

02:04:03.700 | It sent shivers down my spine.

02:04:05.420 | It was fantastic.

02:04:06.420 | I mean, this is the kind of thing that I wanted to experience.

02:04:12.980 | But yeah, so nuclear physics and element creation and formation was really interesting to me,

02:04:18.660 | chemistry, the elements, stars, and all of that.

02:04:20.780 | I was like, "I don't know if I ever find something that combines all of these things."

02:04:26.700 | Then I ended up in Australia, and I met this person, and he was working on old stars.

02:04:32.420 | As I was sitting in his talk, hearing about this for the first time, it kind of clicked

02:04:39.620 | all over my head.

02:04:40.620 | I was like, "Oh my God, it all fell in place because we can use these old stars to study

02:04:46.900 | the elements, to learn how they're formed.

02:04:50.260 | We can get these clean signatures that help us inform the nucleosynthesis processes."

02:04:56.660 | Of course, I need to know a lot about stars, too.

02:04:59.980 | So it's like all together, and that was sort of a moment of magic.

02:05:05.500 | And then the fact that I have now done that for 20 years, it's just like I won the lottery.

02:05:12.100 | It all clicked into place.

02:05:14.420 | In some sense, it's an ongoing love story for me, if I could say it like that, where

02:05:19.620 | I found my stars, my thing, and I am fortunate enough to be able to keep doing that.

02:05:28.940 | I'm happy to see where it will take me.

02:05:33.220 | It's an evolution, as with every relationship.

02:05:38.060 | If you don't march forward, you move backwards.

02:05:40.700 | I'm not interested in moving backwards.

02:05:42.540 | So I'm letting the field and the discoveries and the findings lead me to, and I'm often,

02:05:53.020 | it's not hard for me to follow sort of my hunches.

02:05:56.060 | And sometimes even at the telescope, it's like, "Let's take a look at this one.

02:06:00.780 | I have a good feeling."

02:06:02.020 | And then usually something good or not bad pops out at the end.

02:06:08.940 | And I really like that, A, that I have the freedom to do that, that I'm allowed to follow

02:06:15.220 | my hunches.

02:06:17.120 | Too many people I think are sort of boxed in with their job or their life, that they

02:06:21.100 | don't have that kind of freedom.

02:06:22.740 | That's really important to me, and I certainly try to make use of that.

02:06:25.380 | I also try to teach that to others, to trust them, to learn.

02:06:30.820 | You need to learn your things, but then you need to also trust that knowledge and that

02:06:34.060 | you have a grasp on it, right?

02:06:35.500 | You get out what you put in.

02:06:38.300 | And being able to contribute in meaningful ways to our knowledge about our cosmic ancestry

02:06:46.460 | or cosmic history, that's a wonderful thing.

02:06:53.980 | In this way, your personal love story with the stars evolves.

02:06:59.820 | What advice, you've already spoken to it a little bit, but what advice would you give

02:07:03.620 | to young people that are trying to find the same kind of love story in their career, in

02:07:08.940 | their life?

02:07:10.660 | It seems increasingly hard for folks to find that.

02:07:16.260 | Sometimes I feel that young people have all the opportunities these days, and that's wonderful,

02:07:25.880 | but it's almost like that leads to some, what's the right word?

02:07:30.220 | They're a little bit too tired to make all the decisions because at some point you need

02:07:35.220 | to put your eggs in a basket, and you need to be okay with that.

02:07:39.780 | We can't do all the things, even though we're often told you can be president too, and I

02:07:44.620 | think that's really important to convey.

02:07:47.460 | But at the end of the day, we can only have one job or one type of profession.

02:07:51.740 | I'm not saying you need to be locked in, but it's hard to change 180 degrees.

02:07:59.420 | And so lots of people, I think, are often afraid to really dig in, at least for some

02:08:07.020 | time, and get their hands real dirty and really learn from the bottom up.

02:08:11.580 | On one thing.

02:08:12.580 | On one thing, because they're afraid they're missing out on 99 other things.

02:08:18.580 | But life is a little bit missing out on 99 other things because we only have 24 hours

02:08:23.140 | in a day.

02:08:25.700 | I have that feeling very often.

02:08:27.300 | There are so many things I would like to do, many things I would like to try to be good

02:08:32.580 | at.

02:08:33.980 | Sometimes I wish I had a different job, because I have other interests too, but I realize,

02:08:38.060 | okay, I can only do one thing, so I have no regrets.

02:08:42.560 | But this is a general feeling that I think most of us have.

02:08:48.540 | But if it stops you from really drilling down on one thing, to become an expert on one thing,

02:08:55.220 | to become really good at one thing that you call your own, then it just makes it difficult.

02:09:03.100 | And so a fulfilling life is in part likely to be discovered in the singular pursuit of

02:09:08.820 | a thing, of one thing.

02:09:10.300 | Well, yeah.

02:09:11.300 | Or at least for a time.

02:09:12.660 | Yeah, for some time, with your heart and your hands.

02:09:18.700 | Because I think most people long to own something.

02:09:22.260 | You know, we all, I think, want to leave some legacy of some sort, you know, for our children,

02:09:29.060 | for humanity, for this planet.

02:09:32.840 | And I think it's really important for young people to strive for that and not lose sight

02:09:38.940 | or trade that for all the opportunities, because an opportunity is nothing if you don't do

02:09:43.500 | anything.

02:09:44.740 | You need to do something at the end of the day.

02:09:48.100 | So I chat with lots of people about this, and I often start by just saying, "Hey, tell

02:09:52.300 | me what you don't like."

02:09:53.300 | Because it's often much easier to...

02:09:57.500 | Just narrow down, narrow down, narrow down.

02:10:00.460 | Let out what's not on your plate.

02:10:03.580 | And then this way we get a little bit closer, and then it's like, "Well, why don't you take

02:10:07.300 | a risk?"

02:10:08.300 | Yeah.

02:10:09.300 | And just sign up for something for three months.

02:10:11.220 | But that's what it feels like.

02:10:12.220 | You can afford that.

02:10:13.220 | That's what it feels like, and it is that, is a risk.

02:10:16.060 | Commitment is a risk.

02:10:17.060 | Yes.

02:10:18.060 | Because you're basically sacrificing all the other possible options.

02:10:20.940 | But then I guess you have to trust the magic you noticed in that thing.

02:10:25.220 | Yes.

02:10:26.220 | If you notice one thing, just stick with it.

02:10:28.500 | And then maybe there's something there.

02:10:30.780 | Right, right.

02:10:31.780 | And this moment of kind of feeling it in your entire body and mind that this is the right

02:10:37.220 | thing, getting there is probably really hard.

02:10:42.020 | But if you don't try, you won't find out.

02:10:44.380 | The hard stuff is the fun stuff.

02:10:46.020 | That's also another thing you find out.

02:10:47.660 | And then there is that, yes.

02:10:49.340 | Somehow, it doesn't make sense.

02:10:51.380 | You also mentioned that you've taken a little stroll into the artistic representation of

02:10:58.380 | yourself.

02:10:59.380 | Can you speak to that for a little bit?

02:11:01.700 | Yes.

02:11:02.700 | Well, I already just mentioned.

02:11:05.500 | Sometimes I wish I had more time to do other things.

02:11:09.580 | So I find little sideways, I guess, to pursue things that I like besides astronomy, or at

02:11:17.900 | least I try to find connections.

02:11:19.420 | And so some years ago, again, with the help of my friend who made this Marie Curie movie,

02:11:28.780 | she and I wrote a one-woman play where I actually portray Lisa Meitner, who was an Austrian-German

02:11:37.340 | nuclear physicist from Germany.

02:11:40.780 | So I have the right accent for that.

02:11:45.580 | And we wrote this play about this moment of discovery of nuclear fission.

02:11:51.460 | Again, this is an absolutely critical piece that explains my work today.

02:11:59.340 | And we all stand on the shoulder of giants.

02:12:02.140 | She was one of those giants.

02:12:03.660 | And in some ways, it's of course a way for me to acknowledge other people's work that

02:12:10.260 | have come before me.

02:12:11.820 | It's a wonderful way to highlight the contribution by a prominent woman.

02:12:19.060 | And the way I do it is it's a 25-minute play in costume where I relive for people the moment

02:12:29.100 | of discovery.

02:12:31.320 | Then I turn into myself, and then I give a 30-minute presentation on the art process

02:12:38.000 | and the creation of heavy elements, because the audience can now perfectly understand

02:12:43.700 | that, the public audience, given the historic backdrop of this discovery that they just

02:12:49.780 | lived through my presentation.

02:12:53.420 | And it's a wonderful complement that almost spends 100 years from one woman to the next

02:12:59.460 | passing on the torch.

02:13:02.020 | And when we write up our results in, let's say, in magazines like Nature and Science,

02:13:08.680 | it's always about the results on the golden platter, perfectly prepared.

02:13:15.920 | The discovery is never described, only ever the results.

02:13:21.120 | You asked me beforehand, right, what does it feel to be at the telescope in this moment,

02:13:26.200 | right?

02:13:27.200 | I'm happy to talk about this, but it's nowhere written, never.

02:13:31.880 | Nobody really talks about it.

02:13:33.660 | And so having a form of theater, of the arts, to bring this exciting moment that is what

02:13:43.040 | we all want to experience as scientists to a wider audience is so profound and so rewarding.

02:13:51.100 | And they all love it because everyone can understand a moment of discovery.

02:13:55.460 | I was looking for something, and then I found it.

02:13:58.140 | It's like you misplaced car keys, right?

02:14:02.420 | Or love.

02:14:03.420 | Yes, yes.

02:14:04.420 | Everyone can understand it.

02:14:05.420 | What a glorious experience, yes.

02:14:08.540 | The implications and the findings, that is much harder to understand for anyone.

02:14:15.180 | This is where the scientists' work truly lies.

02:14:18.280 | This is our job.

02:14:19.700 | But the moment of discovery is easy, and it's beautiful, and it needs to be said.

02:14:25.580 | And so taking my audience on this journey, what is the perils?

02:14:30.540 | What are my worries?

02:14:31.540 | And then, ah, here is the moment of discovery.

02:14:35.220 | Let me tell you about it.

02:14:37.180 | It profoundly transformed me, and here's how it went, right?

02:14:42.140 | It's so good.

02:14:43.140 | And art is a way to reveal this fundamental human side of science.

02:14:48.020 | Yes.

02:14:49.020 | The problem with science is that it's people doing it.

02:14:51.660 | Maybe not a problem, but that is it.

02:14:54.700 | That's also what makes it beautiful, right?

02:14:57.460 | Humans are fascinating, and that we're able to come up with these ideas through all the

02:15:01.200 | struggle, through all the hardship, through all the hope, through all the search.

02:15:05.300 | And so the art's a great way to portray that and to broadcast that, right?

02:15:11.340 | I think this is how the audience really should be interacting with scientists, much less

02:15:16.040 | about the findings, but really more about this yearning for answers, right?

02:15:20.540 | I need to find these khakis.

02:15:22.540 | I need it because I need to go, right?

02:15:24.700 | It's like, now, now!

02:15:27.220 | And then, oh, God, here it is.

02:15:28.900 | Now I can go my merry ways.

02:15:31.900 | It's so relatable.

02:15:33.680 | We just need to find more and better ways to do that.

02:15:36.980 | So I hope to turn this into also a digitized version at some point to, again, make it more

02:15:42.500 | accessible.

02:15:43.500 | I hope so, too.

02:15:44.500 | I would love to see it.

02:15:45.500 | So far, I'm just doing it in person.

02:15:48.580 | But it's a nice-

02:15:49.580 | I would love it.

02:15:50.580 | I think a lot of people would love to see it, so I hope you do just that.

02:15:53.900 | Let me ask you a big, ridiculous question.

02:15:56.060 | You look up at the stars, you look up at the early, early, early stars.

02:16:02.800 | So let me ask the big question that we humans often ask and struggle to answer.

02:16:06.900 | What's the meaning of this whole thing?

02:16:10.180 | Why are we here?

02:16:13.380 | - We talked about the biological evolution requires the chemical evolution for all of

02:16:18.020 | this to kind of play out, and carbon played this important role.

02:16:22.100 | And in some sense, we're just a consequence of all of these things being the way they

02:16:27.420 | are, right?

02:16:28.540 | So maybe this is just where we are supposed to be, because the laws of physics sort of

02:16:36.540 | work the way they do.

02:16:38.660 | And we talked much about the variety of everything, really, and certainly from over here to over

02:16:46.500 | there and things in the vicinity of where the sun and the solar system formed, they

02:16:54.260 | were the way they were, and life maybe was a necessary consequence of that.

02:17:00.180 | In some sense, I like to believe that, because then it becomes reproducible, and we can apply

02:17:04.100 | that same argument elsewhere.

02:17:06.540 | If it's total chance, right, that makes it harder.

02:17:09.700 | That's not truly satisfying to a scientist.

02:17:13.380 | - So it's a consequence of psychological evolution, which is a consequence of biological evolution,

02:17:20.220 | which is a consequence of chemical evolution, consequence of physical evolution, whatever

02:17:24.140 | disciplines.

02:17:26.140 | It's turtles on top of turtles.

02:17:28.380 | - Turtles all the way down, yes.

02:17:30.380 | - And you have studied some of the most ancient turtles.

02:17:34.300 | - Yes.

02:17:35.300 | - At the very bottom of the thing.

02:17:36.300 | - That's right.

02:17:37.300 | They live for quite a while.

02:17:38.300 | - Yes, they do.

02:17:40.300 | Well, thank you for your incredible work.

02:17:43.820 | Thank you for highlighting both the human side and the deep scientific side.

02:17:49.020 | It's just, I'm a huge fan of your work, and thank you for everything you do.

02:17:51.860 | And thank you for talking today.

02:17:53.380 | This was awesome.

02:17:54.380 | - Of course, it was wonderful.

02:17:55.700 | Thank you.

02:17:56.700 | - Thanks for listening to this conversation with Adam Furbel.

02:17:59.540 | To support this podcast, please check out our sponsors in the description.

02:18:03.860 | And now, let me leave you with some words from Douglas Adams in "Hitchhiker's Guide

02:18:07.900 | to the Galaxy."

02:18:09.940 | Far out in the uncharted backwaters of the unfashionable end of the western spiral arm

02:18:16.900 | of the galaxy lies a small, unregarded yellow sun.

02:18:21.140 | Orbiting this, at a distance of roughly 92 million miles, is an utterly insignificant

02:18:26.340 | little blue-green planet whose abe-descendant life forms are so amazingly primitive that

02:18:32.660 | they still think digital watches are a pretty neat idea.

02:18:37.740 | Thank you for listening.

02:18:38.740 | I hope to see you next time.

02:18:40.420 | [END]

02:18:40.500 | Douglas Adams, Jr.

02:18:44.500 | [BLANK_AUDIO]

Anna Frebel: Origin and Evolution of the Universe, Galaxies, and Stars | Lex Fridman Podcast #378

Chapters