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

29:13And that sandbox does have super powerful and super expensive telescopes that everybody's also all the children are fighting for the resources to make sure they guess, get the ask the right questions using that big cool tool. Well, can we actually step back on the the big field of stellar archaeology? What is this process? Can you just speak to it again? You've been speaking to it, what is this process of archaeology in the cosmos? Yeah, it's really fascinating. So I mentioned the lesser the mass of the star, the longer it lives. And again, for reference, for the next dinner party, the Sun's lifetime is 10 billion years.

29:57So if you have a star that's 0 .6 or 0 .8 solar masses, then its lifetime is going to be 15 to 20 billion years. And that's an important range for our conversation because again, if you assume that such a small star formed soon after the Big Bang, then it is still observable today. You mentioned old light before. Yeah, that light is like a few thousand years old, but compared to the age of these stars, it's nothing. So to me, that's young. It comes straight from from our galaxy. It's not far, these stars are not far away. They're in our galaxy in the outskirts. They probably did not form in the galaxy because again, hierarchical assembly of a Milky Way event.

30:47Exactly. They formed in a little other galaxy in the vicinity. And at some point, the Milky Way ate that, which means absorbed all the stars, including these little old stars that are now in the outskirts of the Milky Way that I used to point my telescope to. So what can we learn from these stars? Why should we study them? Now, these little stars are really, really efficient with their energy consumption. They are still burning for the experts, just burning hydrogen to helium in their course, and they have done so for the past 12, 13 billion years, however old they are. And they're going to keep doing that for another few billion years.

31:26Same as the Sun. The Sun also just does hydrogen helium burning and will continue that for a while, which means the outer parts of the star, well, pretty much actually most of the star, that gas doesn't talk to the core. So whatever composition that that star has in its outer layers is exactly the same as the gas composition from which the star formed, which means it has perfectly preserved that information from way back then all the way to the day and going forward. So I'm a stellar archaeologist because I don't dig in the dirt to find remnants of past civilizations and whatnot. I dig for the old stars in the sky because they have preserved that information from this first billion year years in their outer stellar atmosphere, which is what I'm observing with telescopes.

32:30So I'm getting the best look at the chemical composition early on that you could possibly wish for. What kind of age are we talking about here? We're talking about something that's close to that, you know, like a 13 billion, 12, 13 billion age range. That's what we think. Now, there's a small caveat here. We cannot accurately date these stars, but we use a trick to say, oh, these stars must have formed as some of the earliest generations of stars because we need to talk about the chemical evolution of the universe in the Milky Way for a second. So I already mentioned the pristineness of the universe after the Big Bang, right?

33:15Just hydrogen and helium. Then the first stars formed, they produced a sprinkle of heavier elements up to iron. Then the next generation of stars formed, that included, again, mass of stars that they would explode again, but also the little ones that keep on living, right? Then the massive ones again explode as supernova, so they provide, again, another sprinkle of heavier elements. So over time, all the elements in the periodic table have been built up. There have been other processes, for example, neutron submergers and other exotic supernovae that have provided elements heavier than iron all the way up to uranium from fear early on.

33:57We're still trying to figure out those details, but I always say pretty much all the elements were done from day three. So iron is where, once you get to iron, you got all the fun you need. Most of the fun. Yes, I know. I really like the heavier elements, gold silver platinum that kind of stuff. For person reasons or for star formation? What's the importance of these heavier metals in the evolution of the stars? So they're the spice of life, right? So every supernova gives you elements up to iron. That's cool, but at some point it gets a little bit boring because that always works, but that's the baseline.

34:47We need that. That certainly came out of the first stars and then all the other supernova explosions that followed with every generation. And it took about a thousand generations give or take until the sun was made. So the sun formed from a gas cloud that was enriched by roughly thousand generations of supernova explosions. That's where the sun has the chemical composition that it has, including, you know, and somehow the planets were made from that as well. So the supernova explosions, the many generations are creating more and more complex elements. No, it just goes all the way up to iron. And then it's just a little bit more of all of these elements.

35:31Just more. Yeah, just yeah, it's one sprinkle than another and it just kind of adds up, right? Now, the heavy elements form in very different ways. They're not fusion made. They are made typically through neutron capture processes, but for that you need seat nuclei, ideally, you know, iron or carbon or something. So the supernova made elements are a very good seat nuclei for other processes that then create heavy elements. And because they cannot be made everywhere, they when you when, you know, so I, my some of my stars have huge amounts of these heavy elements in them. And they tell us in much more detail, something really interesting happened somewhere.

36:14Well, wait, I thought I thought the really old ones we would not have. So what does that mean if the old one? Yes, important clarification. So the stars that we are observing today, these old ones, they formed from the gas. And the question is what enriched that gas? So it could have been just a first star dumping their elements into that gas all the way up to iron. And we have found some stars that we think are second generation stars. So they form from gas enriched by just one first star. That's super cool. Yeah. Then we find other old stars that have a much more complicated heavy element signature.

37:02And that means, okay, they're probably formed in a gas cloud that had a few things going on, such as maybe a first star, maybe another more normal supernova, and maybe some kind of special process like a neutron star merger that would make heavy elements. And so they created a local chemical signature from which the next generation star then formed. And that is what we're observing today. So all these old stars basically carry the signature from all their these progenitor events. And it's our job then to unravel, okay, which processes in which events and how many may have occurred in the early universe that led to exactly that signature that we observed 13 billion years later.

37:54Is it possible to figure out like the number of generations that resulted in these stars? Well, we think we can sort of say, okay, this was like second generation or third because the amounts of heavy elements in the stars that we observe is so tiny. One super one normal supernova explosion is actually already basically too much. It would give us too much of it. And the thing is you can never take away things in the universe. You can only add. There's no cosmic vacuum cleaner going around sucking things away. The black holes are probably the closest to that, but they would have taken the whole star.

38:36Yeah, they'd take the whole thing. That would take them stuff out of the gas, you know, so we have a maybe 10 stars or so now where we're where we are saying that they contain so little of these heavy elements that there must be second generation because how else would you have made them? And again, I want to I want to stress that the elements that we observe in these stars were not made by the stars themselves that we observe. They that's just a reflection of the gas glass. So we don't actually I had to say that because I love stars. We don't at the end of the day we don't really care for the stars that we're observing.

39:13We care for the story that they're telling us about the early universe. So yeah, so the stars are kind of a small mirror. Yeah, into the early universe. Yeah. Yeah. And so what are you detecting about those stars? Can you tell me about the process of archaeology here? Like what kind of data can we possibly get to tell the story about these heavy elements on the stars? Yeah, it depends really on what star you find. There are many different chemical signatures. We actually pair up these days our elements signatures with also kinematic information, how the star moves about the galaxy that actually gives us clues as to where the star might have come from because again, all these old stars in the galaxy, but they are not off the galaxy.

40:05That's a small but important distinction. So they all came from somewhere else. So you can rewind back in time to kind of estimate where it where it came from? Yeah, so we kind of really say, oh, it came from that and that door of galaxy, but interestingly enough, so I was I'm just a few days ago. I submitted a paper with three women undergrads. It was so good to work together. And we found a sample of stars that have very, very low abundances in strontium and barium. So very heavy elements. And I had a hunch for a while that these stars would probably be some of the oldest because as I said, heavy elements give you extra information about special events.

40:47And again, finding something that's really low means it must have for that must have happened either really early on or in a very special environment, right? Because we can only ever add. So if you find something that's incredibly low in terms of the abundance, it maybe just one event contributed that max. So we looked at the kinematics, how are these stars moving? And they're all going the wrong way in the galaxy. How is that possible? Well, it is possible because consider come when I would come back to the proto galaxy, the proto galaxy was like a beehive. It just didn't really know what it was or what it wanted to become when it grew up.

41:32So and it was absorbing all these little galaxies to grow fast. Some galaxies, some absorbed galaxies were thrown in going the main way. And some came in the wrong way, huh? Happens. Yeah, happens. But this could only happen early on when, you know, there wasn't left and right and up and down. So stuff would come in from always. So now, 13 billion years later, we're still doing it. Yeah, they're still doing it. And we just looked for stars that have low stratium and barium abundances. And then we look at the kinematics and law behold, they're all at hundreds of kilometers per second going the wrong way.

42:14It's like, dude, you must have come really early on from somewhere else. So we call this retrograde motion. That's a clear sign of accretion. So something that has come into the galaxy. And because they are so fast and it's really all of them, that that must have happened early on. You can't throw a galaxy into the Mickey Ray right now the wrong way. It eventually will turn around. Can you actually just a small tangent speak to the three women undergrads like this little, it's pretty cool that you were able to use a hunch to find this really cool little star. Yeah, what's the process of like, especially with undergrads?

42:56I think they'll be very interesting and inspiring to people. Yeah, so it was a wonderful little collaboration that actually emerged in the fall. So I like, I really like working with undergrads and grad students, postdocs. And I came up with a new concept for a class at MIT where I wanted to integrate the research process into the classroom. Because sometimes people find it really hard to call email a professor, hey, I'm this and that person and I'm interested in your research could possibly come. And I wanted to streamline that and give, and not just trial, how it would work to provide a sort of a safe confines of a classroom where you just sign up and do research in a very structured way.

43:52And I developed it was a lot of work, a little bit more than I thought, to map up an entire research project basically from scratch in 10 work sheets so that they could do it again in a very structured and organized fashion. So you created this whole framework for it to do it. The whole thing. But the promise was, you come sign up for my class in teams of two, you each get your own old star that has not been analyzed before. I don't know what the solution is because in research, we don't look up the solution at the end of the book. We do not know what we're going to find. Our job is to do the work and then to interpret the numbers because our job as scientists is to find the story.

44:39Yeah. Anyone can crunch numbers. Anyone. It's it's to find this complicated sometimes, but it's doable, right? But coming up with a story, when you only have three puzzle pieces, what does the puzzle look like? That you have to be a little bit bold. You need to have some experience and you need to kind of see the universe in 3D. You just need to kind of go for it. And that's the beautiful thing. I really love that. And so this was a story of weird kinematics going the wrong way combined with this particular weird signature in terms of the elements. Exactly. And you have to come up with a story.

45:16Yes. And so the story of that paper is now, usually I don't say I find the oldest stars, you know, when I talk to my research colleagues, I talk to them about we find the chemically most pristine stars because that's actually what we measure, the chemical abundance that tells us, okay, it must have been second or third or fifth generation of stars, right? But these low strong -femestars that go in the wrong way, like they're getting paid for it, they must be the oldest stars that came into the galaxy because they formed before the galaxy was the makeaway, right? And it's so cool. And it was so wonderful.

45:55So this class, it went so well in the fall, I had nine people sign up that that's not unusual for a class at specialty class at MIT, so small number. It was eight women and they were so into it that I said, okay, let's use this opportunity. You're going to do some extra work with me and we're going to publish this. Try to publish. Yes. I also like that you're using the terminology of chemically more pristine. When I'm talking to younger people, I'll just say that I'm more chemically pristine than them. I like that description of age. So there's this term of metal poor stars. So most of these old stars are going to be metal poor.

46:38Yes, I searched for the most metal poor stars. And what is that can we just define? Yeah, what does that mean? I don't know who came up with this. I would love to know, but the universe is a complicated place. So many decades ago, someone clever came up with the idea to say, let's simplify things a little bit. Let's call hydrogen X helium Y and all the other elements combined metals Z.

47:09When I give public talks, I was asked, I said, I said, Neon is a wonderful metal. Oh my god. What's he saying? I'm in astronomy. I'm not a chemist, so I'll get away with it. So if you just roll with it for a moment, all the elements except hydrogen and helium are called metals. Now, if we look again at chemical or the concept of chemical evolution, it means more and more off all the elements, everything higher than hydrogen helium gets produced slowly, but surely by different types of stars and events. So that's a monotonously increasing function. And so we look for the stars that have the least amounts of heavy elements in them, because that means we are going further and further back in this process in that function, almost all the way to the very beginning.

48:05And that is the first stars, right? They started that process. That's why I said it was such an important transition phase, because it thinks we call the post -big bang universe pristine, just hydrogen helium. And after that, the mess started. If you soon as you add elements to it, things kind of get a little out of hand. That ends in this beautiful variety that we have everywhere these days. And you're looking at the very early days in the introduction of the variety. Yes, exactly. When it was still a little bit more organisable. But the variety of different types of metal per stars, we have a stark, many different types of stars, many patterns we have sort of identified, but they are still crazy ones out there that we're still trying to kind of fit in.

48:58So what kind of stars have been discovered? So you've already a while ago helped discover the star H .E. 1327, 2326. Great name. Yes. And H .E. 1523, 0901. What can you say about these stars and others that have been found? I love them. They're my baby stars. What do you call your baby stars? Well, I'm the only one who can spit out these names without cheating. Are there snake names? Are there snake names? No, that's not allowed. While some colleagues at conferences have just called them Anna star, freeble star, because they didn't want to learn the phone number. I get it. Phone number. These numbers are actually based on older sets of coordinates for these stars.

49:49So the minus in the middle means that they are in the Southern hemisphere. So negative is in the Southern hemisphere positive is in the northern. And then 13 and 15 means that sort of observable in the middle of the year. Okay. So it's the doing with the observation and where was observed? Yes. Yes. Yes. But they have very different stars. Both absolutely significant career defining actually for me, but really pushed the envelope in very different ways. So 1813, 27 of the first one that you mentioned, that was the second, second generation star that we found. And usually people say like, oh, the first one is the big one and the rest is nobody cares.

50:32But to us, it proved that yes, we can do it. Because one, astronomers live in this sort of way of, you know, there are a lot of serendipitous discoveries and we, that's really great. But we need to show that we can do it again. Reliably. Because then we're on to something. And it's not just some kind of weird quirk. And there are a lot of quirks in the universe. But we want to know, is that a real thing? Does that happen regularly? Is there something that we can learn? Is that a piece of the story? And so finding the second one that was even a little bit more extreme than the first one really showed, yes, our search techniques work.

51:13We can find these stars. They provide an important part to the story in a sense that if we had more than two stars, and by now we have about 10ish or so, what do they tell us about the nature of the very first stars? And what we found again, working with the theorists, of course, who run these supernova models, is that, so actually, let me, let me, before I get into this, these two stars had huge amounts of carbon relative to iron. So we usually use iron as a reference element for what we call the metalicity. So the overall metal content, the overall amount of heavy elements in it. So that's why it's called iron deficient.

52:04That's right. So these stars are incredibly iron deficient, which means there must be of the second generation because there was an interestingly enough, there was this discrepancy, a normal supernovae, until then we thought would get us so much iron, you know, you would distribute that in the gas cloud, and then you would form this little star that we're observing. But the iron abundance that we measured was actually much lower than that. And I already mentioned, you can't take things away. That must mean these early massive pop three, we call them population three, the first stars, they must have exploded in a different way than we previously thought.

52:47They can't output as much iron because they just can't otherwise it wouldn't match our observations. Got it. And so that's when we started to work with several theory groups on supernova yields. So what comes out of from the explosion of the supernova, that's cool, supernova yields. And so this one was not yielding much iron. Well, we needed to concoct a theoretical supernova that made less. And it's actually surprisingly difficult because you can always add more in the universe, right? But you can't take stuff away. So Japanese colleagues kind of came up with the idea of a feinter supernova that just doesn't have much enough oomph, you know, when it explodes.

53:37So somehow there's less iron coming out. But at the same time, then these stars showed huge overbundances of carbon, you know, a thousand times more carbon. So how do you now get a thousand times more carbon out of these poor first supernova, you know, that was the theoretical challenge. And because we didn't have just one star, but two, that really spurred the field to think about what was the nature of the first stars? How did they explode? What are the implications? Because if they are not as luminous and bright and energetic, that has consequences for these early proto -galaxies in which, you know, they must have been located in terms of, you know, blowing the gas out, let's say, in disrupting the system.

54:26So much higher chance for the earlier system to stay intact for longer, right? So there's a whole tale of consequences. And this is what I mean with we need to find the story because you do one thing and it's like the dominos, the consequences everywhere. And then you have a different universe, right? So what could possibly be a good explanation for something that yields a lot of carbon, it doesn't yield a lot of iron? Well, it's not so much an explanation, more like finding a mechanism for what happens in supernovae and the official term, what was sort of, as I said, co -cooked up in order to explain the observations.

55:06And we have, by the way, found a whole bunch more of these stars, so that holds. And it's called a fallback mechanism. So actually in the supernova, during the supernova explosion, a massive like hole emerges. And so some of the material falls back onto the black hole. So here is a vacuum cleaner now plopped into the middle, right? Like a temporary one that just cleans up some of the elements. Well, sort of, right? Because if you think of the, we haven't talked about this yet, but if you know what a story looks like, a massive story looks like on its, on its, in its interior, before it explodes, you have hydrogen helium still on the outskirts.

55:43And then you have your layers of heavy and heavy elements all the way up to iron. So you have an iron core in the center. And because you can't get any energy out of iron when you want to fuse to iron atoms anymore, right? That's when the supernova explodes, or occurs, really. It's actually an implosion first. And then you have a bounce of the sort of neutron star phase that that occurs in the process. And then it's so awesome. It gets disrupted. Yeah. It's like this giant, you know, basketball, and then, whoa, it all goes out. Explosion first explosion. Yeah. And so in the process, right? If you make your black hole basically big enough, it will suck away some of the iron, because that's the closest in the in terms of the layers, you, you, you, you, you hold onto it.

56:30You don't let it escape. And carbon is much throughout. You let it all go. And so that explains why you can have a big oomph and not much iron yield. Yes. Yes. So is this explained the H .E. 1327? Correct. And others like it. Yes. So there's a, there's well established now that the lower the iron abundance of the stars are, the higher the carbon sort of gets. And carbon is such an interesting element in that regard. If we come back to the formation of the first low mass task, right? So we had the, the hotter gas, just hydrogen and helium that made the first stars. They were 100 solar masses also, because it could, the gas couldn't cool enough.

57:18So they were big and puffy. Carbon then coming from the first stars probably led to enough cooling in these gas clouds that enabled the formation of the first low mass task. So think about what happened if there wouldn't have been any carbon or the properties of the carbon atom would be different. It would not have cooled the gas in such significant ways, perhaps. There wouldn't be any low mass task. We wouldn't be here today, right? And we're carbon based. And so I think carbon is really the most important element in the universe for, for a variety of reasons, because it is enabled this whole evolution that we are now observing and literally seeing in the sky.

58:03And it's fairly fascinating. So combined with the fact that you have the iron deficient, so all of that is probably important to creating humans. Yeah. Yeah, we need all the elements. But if you don't have stars, you know, like the sun, small stars, that can actually host planets that have long lifetimes. You need long, long lifetimes if you want to have a stable planet and develop humans. The carbon is kind of important in many ways. Yes, yes. This is perhaps a interesting tangent. If I could just mention that you interviewed military dresselhaws, carbon queen, the remarkable life of the nano science pioneer.

58:44Is there something you could say about the magic of carbon and the magic of millie? Well, millie was certainly magic. She was a professor at MIT for many decades. I met her a number of times. Her photograph, actually a young and an older millie is still on the wall every time I step out of the elevator in one of the buildings I see it. She pioneered all sorts of carbon nanowork, so she is a was material scientist. Very far removed from what I do in a daily basis. But yes, carbon has amazing properties when you study it. And again, that's indeed another aspect of why carbon is so fascinating, not just in the cosmos, but also for us, you know, making us, creating us in a way that we can use it.

59:41It's wonderful. You sometimes think about this chemical evolution in this big philosophical way that we're where the results of that chemical evolution, like we're made of this stuff. We're made of carbon. Yes, we're made of store stuff. Yeah. And it came. Got right. I mean, it's almost like a cliché statement, but it's also a material, a chemical or physics statement that came from hydrogen and helium. And somehow this formation created this interesting complexity of soup that made us. What are we supposed to make of that? Like, what, do we just get really lucky? Why do we get all this cool stuff?

1:00:23Yeah, that's a good question. I don't think it's a question, there's an answer. I keep just asking why. But it's just this incredible mystery. So much cool stuff had to happen. So much, sorry, hot stuff had to happen. And so much could have gone wrong and there would have been another outcome, you know, and it's actually amazing how many things kind of fell in place. I mean, maybe that's also sort of soft deterministic in some ways, right? We are who we are because that was the path. Maybe we wouldn't have ended up being robots. I don't know. But it's certainly wonderful to, you know, as scientists for us to help contribute and rambling our cosmic history.

1:01:10I always say the biological evolution on Earth was, you know, absolutely facilitated by the chemical evolution of the universe, right? And one doesn't go without the other. And that evolution, that evolution seems to be creating more and more complexity. The kind of interesting clumping of cool stuff seems to be accelerating and increasing. And it's hard not to see as humans that there's some kind of purpose to it, like a momentum towards complexity and beauty, you know? Well, beauty is in the eye of the beholder. But yes, everything gets more complicated. Well, there's also beauty to the chemical pristine universe in the early days.

1:01:55Certainly, yes. I love the desert with its nothingness. Yeah. That it has so much aesthetics and appeal. We came from nothing, we'll return to nothing. So what about HE 1523? What's exciting? A red giant star? Yes. That's another one of your babies. 13 .2 billion years old. Yeah. So that one isn't quite as iron deficient as the other one. So probably not a second generation star, but easily second third, sorry, third, fourth, fifth. So we can't really pin it down. But it's also not super important for us. What is important is that that star has a very different chemical composition in a sense that yes, we have all the elements up to iron there.

1:02:46They have sort of normal ratios, which means kind of the same as most other old stars and not too different from the Sun or at least different in quantifiable ways. But it has this huge overload of very heavy elements. And what was so nice about that, Stan, particular was that I could measure the thorium and the uranium abundance. And again, that was the second of its kind. But the uranium abundance could be more well determined. So we had a better grasp on that. Now, why a thorium and uranium interesting, they are radioactive elements. They decay. Thorium has a half -life of 14 billion years, I believe, in uranium of 4 .7, which two folks on us on Earth is a really long time.

1:03:46But those kind of timelines are really good when you want to explore the early universe. So there are two questions now that kind of come to mind. Where do these elements come from? And what do they tell us? And these as we know, these heavy elements are made in a specific process. It's a neutron capture process, usually referred to as the R process for rapid neutron capture process. We talked about seed nuclei before, right? So we still don't exactly know where this process can occur. So you have, let's say, a lone iron atom somewhere. And it is in an environment where you have a strong neutron flux, which means that it must be lots of neutrons around.

1:04:36And again, when we talk about the site, we can submyze and ponder where that might be the case. But you have this iron atom and you bombarded with neutrons and you do it incredibly fast. Now what happens in the process? That iron atom, you collect lots of neutrons, it becomes really big and unstable. So it's a heavy neutron rich nucleus that wants to decay because it's not stable, it's way too big. And so let's say you add only one neutron to it, that would already make it unstable. So it will then, it has a characteristic decay time that's called the beta decay time scale. So it will decay to a stable nucleus.

1:05:19So the neutron will convert to a proton and that makes it stable. If you know bombard lots and lots and lots of neutrons onto that seed nucleus within that time scale of the beta decay, that's how you get to this huge fat neutron rich nucleus that then wants to decay. So the rapid processes, you have your seed nuclei, they get bombarded, you create these really heavy neutron rich nuclei, they are heavier than uranium even, the neutron flux stops and then all these heavy nuclei, they decay. And they make all these stable isotopes that we know of all the way up to thorium and uranium. So that rapid nuclei decay will create all the fun.

1:06:07Correct. And the whole thing is done within two seconds. So just to add to the rapid here, literally the snapping on my hand, it's all there. In my talks, I often, I have this nice simulation that illustrates this creation of these wrap of these heavy nuclei. And I always say, this is the only simulation you will ever see that slower than real time. Because in astronomy, you know, we show, oh, this is how galaxy forms, 13 billion years and 30 seconds. Really short, right. This is the opposite. Me showing you this, the elements are long, long made. So where and when does this happen? Does this process happen?

1:06:51So you need the strong neutron flux. That's the clumping of the neutrons. Yes, that's right. And so there are not that many options, right. So where do you find lots of neutrons in the universe? So it's neutron stars, right? Neutron stars form in the making of supernovae of the explosions. Okay. So maybe some of this heavy material gets sort of made in the making of the supernova explosion and then gets expelled. Or you have neutron stars. So the, you know, if the neutron star, so I mean, usually that's the leftover of the supernova. If you have two from a binary pair. So stars usually actually show up in pairs.

1:07:34And so it's not too unusual to create a pair of, of neutron stars that will still orbit each other after both of their pretendeta stars have exploded. And those two neutron stars will orbit each other diligently. But as we know now, thanks to LIGO, the gravitational wave observatory. I mean, we know already that before but now it's been measured by LIGO is that these two neutron stars, they will orbit each other for like forever. But in the process, they will, they will lose energy. So that orbit is what we call the orbit decays. And eventually the two neutron stars will merge. And that results in an explosive event that has roughly the energy of a supernova.

1:08:22But the process is completely different. And the cold thing is when these two neutron stars collide, they produce a gravitational wave signature because neutron stars are super dense objects. They are like giant atomic nucleosis. So there's a lot of interesting physics happening already. And so if you basically form a super neutron star by smashing two into each other, more interesting physics happens. And that means that this is ripple sent out into the space, the space time continuum, basically. What do people say? The ripples of space time. It's like you drop a rock into water, right? You see the waves coming.

1:09:06So that's exactly what happens when two neutron stars merge. And this is neutron's galore, right? It's really violent to smash two neutron stars. So that are so dense already into each other. And they in 2017, one of these events occurred. And the LIGO and Virgo gravitational wave observatories, they detected that. And then the astronomers pointed their telescopes in that direction. And they indeed observed what we call the electromagnetic counterpart. So there was something seen in the sky that faded over the course of two weeks. And that light curve, that light was exactly what you get when you create all these heavy neutron rich nuclei in the R process.

1:09:58And then the neutron flag stops. And then it takes about two or three weeks for most of them of these nuclei to decay to stability. So we saw, the astronomers saw in this electromagnetic counterpart, the nuclear synthesis of heavy elements occurring. And that's just. That's amazing. Awesome. So that's a electromagnetic counterpart to the gravitational waves that were detected with two neutron stars colliding aggressively violently to create a super neutron star. And that's where you get all the neutrons and neutron flux somehow. And then that the whole shabay that happens in two seconds and creates a bunch of things.

1:10:41So that confirmed that one of the sites for sure is for the R process to occur is neutron stommergers. Interestingly enough, I have to mention this here, a year prior in 2016, my former grad student Alex G and I we discovered a small drawer of galaxy that is currently orbiting the Milky Way. It's called reticulum two. That was full of ancient iron deficient stars that also had a strong signature of these heavy elements exactly like 181523. We weren't looking for that. I actually wanted to prove that they had really low levels of heavy elements because that's what we had seen in all the other dwarf galaxies.

1:11:28And I was dead set on showing yet that that is yet the case again and that that is a typical signature of early star formation. We already talked about low strontium and barium abundances and the oldest stars, right? This is what we had seen anecdotally in in the ancient dwarf galaxy that are surrounding us. So that's an ancient dwarf galaxy though that dwarf galaxy has a bunch of ancient stars in it. Yes. Yes. And so now we find reticulum two and it has these the stars show the signature of the rapid neutron capture process, the R process and we are like, okay, these stars are located in a dwarf galaxy right now.

1:12:08We have environmental information. They are not lost in the galaxy where we don't know where they actually came from. Now we know these stars were formed in that galaxy because they're still in it. And that we already deduced from that that it must have been a neutron star merger that went off in reticulum two at early times that polluted the gas from which all our little stars formed. Can you speak to what a dwarf galaxy is? Can you speak to what this reticulum two dwarf galaxy is that is orbiting the Milky Way galaxy? Yeah. It's going to be eaten by it presumably as stuff. Totally is going to be eaten.

1:12:41I can't tell you exactly when. Yeah, the Milky Way remains surrounded by dozens of small dwarf galaxies. There are collections of stars. Some of them we call them ultra -faint dwarf galaxies because they are now only contain I don't know a few thousand stars. They are very very faint. They're still detectable. Yes, because they're fairly close and we detect actual individual stars so I've observed some of the faintest stars. You know, you possibly observe with current telescopes in these dwarf galaxies because I was like, I need to know what the chemical composition is because there are leftovers from the early universe.

1:13:22They did not get eaten. So they're still in their native surroundings. It's like getting the lions in the wild right? I got to study those. And compare to the counterparts that got eaten and are now in the Milky Way. And so I... So presumably most of those stars is not all those stars in that dwarf galaxy. They're really ancient. They're all really ancient because actually as it turns out, if you have a small galaxy, there was a process early on in the universe called re -ionization that kind of heated up everything. And together with some supernova explosions in an early shallow, you know, bound system, all these little systems lost their gas.

1:14:06It was sort of blown out or it simply evaporated or both, probably both. And so these systems have been unable to continue to form stars since. So it's the best for us to say archaeologists that you could hope for because it's a whole bunch of stars still sitting there. It's not just one. It's a whole bunch of them still sitting there ever since and literally nothing has happened to them. They've just been waiting there for us. So from the stellar archaeology perspective, what is like Juicier and more interesting? The old stars and the outskirts that have been eaten are the outskirts of Milky Way or the the stars in the dwarf galaxies.

1:14:49What's of all the things you love about the world?

1:14:58You said it's a hot one. I mean, I love them all, of course. They serve different purposes. The stars in the Milky Way, I can get much, much, much better data for them because they're brighter, they're closer, so they're brighter. And that tickles my fancy. And they have interesting kinematics presumably. Yes, and we can get that. And so, HG 1523, for example, you know, that one is really bright, only it's a red sign, so it's intrinsically bright and it's fairly close. And so the data I got for that was insanely good and that yielded this uranium detection and thorium detection. I can never get that kind of data for dwarf galaxies.

1:15:39So that's a big trade off. But the environmental information that we get along with the basic information of these stars in each dwarf galaxy is really, really valuable in establishing, you know, these, for example, the site information, right? Because the galaxy is still there, so nothing crazy could have happened. So it should close that loop. Probably some heavy elements come out of supernovae here and there, but somehow my theory colleagues tell me that the normal supernova just doesn't have enough oomph to really get that our process going and doing it, doing it all. So you need these orbiting supernovae.

1:16:18We need them, the probably the neutron star mergers, or we need a special kind of supernova that's maybe extremely massive or heavily rotating or does something else funny, right? To really kind of get that particular process going. But the normal supernovae don't do it, right? So only a little bit comes up, but you could come along and say, and why don't you just take 100 supernovae together to build up the yield, right? But then I come along and say, like, look, this dwarf galaxy is still intact today. If you would have plugged in 100 supernovae into this little system early on, it would have blown apart.

1:16:50It would have blown apart past five supernovae or 10. So that's a really important constraint that we have that these systems are still alive, right? So it helps us to pin down where certain processes could have possibly happened. And so it's just a different type of information that we get. Maybe amazing if we could talk about the observational aspect of this, the tools of observation. So what telescopes have you used? Do you use? And what does the data look like? And I think I've read a few interesting stories about the actual process of day -to -day observation, a bunch of probably late nights.

1:17:30Well, yeah, astronomers are doing it all night long. So we have lots of late nights. Can you explain the all night long aspect of it? Well, let me start by saying, I mostly these days use the Magellan telescopes in Chile. They are 6 .5 meter telescope, which means the mirror diameter is 6 .5 meter. That's not the largest that is out there, but it's among the largest. And I use a spectrograph because I'm a spectroscopist. I don't take pictures. And that particular spectrograph at that telescope is actually unusually efficient. So it kind of makes up for the fact that the mirror isn't as large in, let's say, the 8 meter telescopes from the European.

1:18:15So so I'm very happy with that. Efficiency meaning. How many photons get collected sort of per time unit? Because we that that's always the limiting factor. Prior to the pandemic, we would travel to Chile to do our observations. Those telescopes are the that's the last observatory where people were sort of supposed to travel there and take their own observations. Most other observatories basically have staff there by now who take the observations for you. So there's the directly the scientists are specifying where to point the telescope and the sitenering collecting the data makes sure the data is collected well, the cleaning of the data, the what offloading of the data, all that kind of stuff.

1:19:03Yeah, so it's mostly done for them. Yeah. And obviously that's super convenient. But it also takes takes away a central part of the work of an astronomer is which is data collection. Right, we don't have an experiment in the basement where we can go day and night or whenever we please and ask a certain question of the apparatus. Right, let's turn this knob and see what happens. Let's turn that knob and see what happens. No, you know, we only have one experiment, which is the universe. And we what we see is what we get. And I think it's so important to take an active role in that. So I really love going to the observatory.

1:19:49I've taken many students there over the years to teach them and to just show them what it means to to be an astronomer because you go to these remote mountain tops and it's such a magical environment. And you wait there, you know, for the sun to go down and then you get ready and you look outside and it's such a serene environment. It's a little bit out of this world. You're sitting there. So the sun goes down. It's evening, late evening. And what does it look like? What are some of the most magical experiences of that process? Well, you know, when you're on top of a mountain, you know, climbers, I guess, get to see that probably otherwise.

1:20:37It's very calm. And the colors are so beautiful. And I always become much calmer when I'm there. I'm just A, because I'm just there for one purpose only in that data collection. I can say no to my emails. I can say no to everything else because I'm observing. So there's literally less, less distractions because you know, you're just there to do one thing. And also the emails somehow seem less significant. Yeah, yeah. It's just you can't afford to focus on just one thing. And you it just kind of does something to you. It's a little hard to describe, but you know, if you then fast forward, maybe I can speak a little bit about that.

1:21:24And I have done a lot of astrophotography there as well. And I observing faint dwarf galaxy stars, you know, these are like 45 minutes, 55 minute exposures. So you actually have a lot of time. So I would run outside and just lay on the ground under the southern Milky Way. Beautiful, right up, you know, and I would just lay there like the snow angel, you know, and just stare up there and just kind of let my thoughts sort of pass through my brain and just like I'm one of it, right? We talked about this in the beginning. This is when I personally have the feeling that I'm a part of it. I I belong here rather than feeling kind of small.

1:22:08Yes, I'm small, but so many other small things and lots of small things make one big hole. And we're part of that big hole. And so that's looking at the inner spirals. Yes, and just, you know, this dark sky with the bright stars. And I have described this in my book years ago, if the Milky Way is all bright above you, you don't need a moon or anything. You can walk in the starlight and you will find your way. There are no trees there for safety reasons, but you wouldn't even run into a tree, right? I mean, you can see, you can almost see the shadow, you know, from from the starlight because it's such a dark side and the stars are so bright and these are kind of moments that that kind of change you a little bit.

1:22:56And you see the unity of it all. Yeah, and it's just you and nature and, you know, with modern civilization and all of that, I think we often try a little bit too hard to be removed from nature, you know, to be independent of it and figuring it all out. But at the end of the day, we're just a part of it. And that really helps me to remember that, that, you know, we're one in the same. Well, that fills me with hope that could I tend to think of us humans as in the very early days of whatever the heck we are. So that makes me think thousands, tens of thousands, hundreds of thousands years from now, there will be reaching, whatever we become, will be traveling out there to explore more and more and more.

1:23:45Yeah. So we're what you're doing is the early days of exploration with the tools we have. Yes, the early seafarers looking at the sky for navigation. Coming up with different theories of what's on the other side, that the earth is starting to gain an intuition that the earth may be around. And then we might be able to navigate all the way around to get to the financial benefits of getting spices from India, whatever the reason, whatever the grant funding process is all about, but ultimately actually results in a deep understanding of the mystery that's all around us. And I mean, it's just to travel out there.

1:24:23And to me, the discovery of life in the solar system, I really hope to see that in my lifetime. Some kind of life, bacteria, something, maybe dead, because that means there's life everywhere. And that's just the kind of stuff that might be out there. All the different environmental conditions, chemically speaking, that are out there. And it just seems like when you look at earth, life finds a way to survive, to thrive in whatever conditions. And so maybe that process just kind of humbles you as a super exciting to know that there is life out there of different forms. And of course, that raises the question of what is life even?

1:25:14We're down to have a very human -centric perspective of what is a living organism and what is intelligence and all this kinds of stuff. And all the work in artificial intelligence now is starting to challenge our ideas of what makes human being special. And I think we're doing that through all kinds of ways. And I think you're working some part during that as well. Like the unity you feel is realizing where we're part of this big mechanism of nature, whatever that is, that's creating all kinds of cool stuff from the humble, pristine origins to today. So if you could just kind of linger on the process of the data, what does the data look like?

1:25:56And how does the raw data lead to a discovery of an ancient star? Well, as a spectroscopist, we have to talk for a brief moment about what a spectrum is. Yes.

1:26:13Everyone, I hope, has seen a rainbow on the sky. That is basically what we're doing. We don't send the starlight through a raindrop that then gets bonds around and splits up the light into the rainbow colors. We do it with a spectrograph, so basically a prism. So we send the starlight through a prism of sorts and that splits it up. And then we record exactly that. So it's a little 2D picture actually of a spectrum. Now it's not going to look colorful. It's just like what black and white, different colors have, of course, different energies. That's what we record. More specifically, we record it as wavelengths, so wavelengths and frequency and energies all the same at the end of the day.

1:27:08We process that little image in a sense that we do a cross cut and then sum up a few columns so that we get all the data that we recorded. And what we see is a, it's a bit funny to describe just with words, but a wiggly line with lots of dips. So the 2D process spectrum, we call it continuum, so it's just a flat line, basically, and then there are dips. So the interesting things are the dips. If you think back of the rainbow, what we actually see in our stars is not just a rainbow, but it would be a rainbow with lots of black lines in it, which means certain little pieces of color have been eaten away by a certain amount.

1:27:53And so we can no longer see it as well, we're not at all. Why is that happening? So if we come back to our stars, what we're observing, we're observing the stellar surface, we can actually never peer with our telescopes inside. We only ever go, can go after the surface. And the surface contains, or the surface layer contains different kinds of elements. Every one of those types of atoms, so elements are just different types of atoms, they absorb different photons that are coming from the hot core where the fusion is occurring. And so that means that if you were the observer, with a spectrograph or without, you will see the starlight, but certain frequencies, certain energies of that light will have been absorbed by all the different atoms in the gas.

1:28:48So you see less of them. And so that's other dips. And the strength of the dips tell us, you know, which element was it? And how much of that element was or is in the star? So we have many, many, many dips. The solar spectrum for reference, you know, all the dips are overlapping because the abundance of all the elements is so high. It's actually very complicated spectrum. My spectrum really look like a straight line, and then there's a dip here, and then there's the straight lining and there's a dip there. The sun doesn't have straight lines. I mean, that's just all absorbed in some form or another.

1:29:28But the old stars have so little off all the elements that they're only occasionally these dips that then indicate, okay, that one at that way, Flanks was iron, and here we have carbon, and there's magnesium and sodium. Oh, there's a little strontium line here. So we have a much easier way to map out this bar code that this spectrum, you know, pretty much is at the end of the day. And to then measure the strength of these, we call it absorption lines to then calculate with existing codes that mimic the physics of the stellar atmosphere, like how much was absorbed, how many, what, what kind of elements were, were present in in the stellar atmosphere.

1:30:12And so this is how we get to our abundance measurements, and then all together that gives us the the chemical composition and that particular signature in that star. If you, do you ever look at like the raw spectrograph and the absorption line, and they're able to see into it some interesting, non -standard outlier kind of patterns, or does this have to do heavy amount of processing? We actually process our, it's fairly straightforward to do our processing. We do it at the telescope. So I often take a shorter exposure first, let's say 10 or 15 minutes. So mostly when I do discovery work, we would just take a quick look spectrum, then we process it while we observe the next star, then we take a quick look.

1:31:05We have what I call the summary plot. It's a collection of little areas in the spectrum that have the key positions, the positions of the key elements in it, and it's kind of like reading the tea leaves. I have stared at so many spectra. I just need to know, I just need to see our summary plot and I can tell you exactly what the numbers are going to be. And also to tell if it's going to be promising to get further. Exactly. And so that's thumbs up, thumbs down. Are you worth my time or not? In most cases, it's not, or it's good enough, we can do a basic analysis, maybe publish this as part of a larger sample, just so we output that we have observed this star and they're a basic nature that's an important part to publish as well.

1:31:52And yeah, I had a run, so now we do remote observing. I do all of this now from my home, for my living room all night long. And I often work with colleagues, so we do it over Zoom and we process the data, we look at it, same thing still. And we just found a star that had a very low iron abundance. And then we decided, okay, that looks interesting. We're just going to keep exposing. So we'll talk more data on it on the spot and we're writing up the paper right now. How do you know where to point the telescope? It's not random. There's a lot of work that goes into that. I began my career by answering, trying to answer that question as in like doing the search process.

1:32:43That's why I called my book that I've written some time ago, searching for the oldest stars because searching is one thing, it's very time consuming. And then on top of that, not everyone finds, right? I often don't find, but I keep searching because techniques have established that, yes, we can do it if we're just patient enough and keep going because it's a numbers game. And that's often the case in science. And that's something that not enough is talked about, how tedious it is and how long it takes to get to that one discovery, right? That that moves the field further. And how difficult it is to believe that there is a thing to be discovered?

1:33:30Yes, yes. We have the saying, I learned this, I think, from my supervisor. One star is a discovery. Two is a sample and three is a population. So as soon as you found three of roughly the same kind, you're done. But you need to get there. Probably the first is the hardest, right? Yes, but it kind of remains really hard. And but the thing is that at past three, many of us are okay, we solve that problem. We've done it three times, so we can do it. That's a thing, right? That's a population, three iron deficient stars, let's say, right? That's one puzzle piece. Now we can move onto the next thing.

1:34:14That's an indicator that there's many more of them. Yes. Potentially. Yes. Yes. Yes. So to cut a long story short about the searching, we started early on with what's called low resolution spectroscopy of many stars. So for example, my thesis work almost 20 years ago was piggybacking off a quasar survey that had collected. So quasars are basically giant supermassive black holes that are really far away. So you only see one big bright light point. So it looks like a star, but it's actually just a giant supermassive black hole that outshines its its own galaxy. And people had been trying to study those and they had taken little spectra of, you know, all things in the sky.

1:35:01And it turns out, oh, you can't fish out the actual stars from that and look for certain signatures that might indicate low -medalicity stars, so stars with low abundances. And so it was painstaking work to then take medium resolution spectroscopy to get a little bit more information and to use approximations and to kind of get candidates that we can then eventually take to the big glass like Magellan to get a high resolution spectrum. So we really see the dips of all the individual elements that then give us a final answer as a yay or a. These days with another grad student, I just I developed a new technique to use images actually of all the stars in the sky taken with very narrow filters.

1:35:50So it's like you're wearing very specific glasses that only let so much light through. And so we can do similar things through having several narrow band filters, what we call it, to fish out things that have, you know, no absorption over here. So just the straight line and then a little dip here. So a little something there. And that has proven fairly successful in recent years. So looking at the entire, looking at broader regions of the space. That's right. Because these stars are a little bit like the needle in a haystack right there. Not that many left over. And the certain new the galaxy has made plenty of stars in between.

1:36:31We need to comb through all of those to to get to the goods. So we always start with millions and then work our way down. And in the end, we have like three good candidates. I wonder how those ancient stars feel that they were noticed. They probably know that nobody pays attention. I'm just kidding. We're all special, right? So other stars. It's good. It's inspiring. Even if you're the alchast in your pristine nature, you still might nevertheless be noticed. I'm hoping the same about humans if somebody's observing us. Is there something else you could say that's about the challenges of this kind of high precision measurement that you're doing.

1:37:14So this kind of collection of data, looking, trying to pull out the signal from the noise out there. Well, that's literally what we're doing in multiple ways. Actually, we find trying to find the needle in the haystack. And then we find something. And then it turns out it's just a little bit too faint to actually get the kind of data quality on it that we would like or that would would be warranted given the potential of the star, right? It was like, so there's always noise. There's always a little bit of noise. And you have to try to say like, how special is this when you're looking at the absorption line?

1:37:55Yeah. So the most iron twostas, their iron lines are so tiny that they're literally, you know, almost in the noise. So you need incredibly good data to make detections. And the funny thing is we're looking for the nothingness of let's say the iron lines. But then we don't want nothing because if there's nothing in the spectrum, we can't measure anything. We can only get an upper limit. But we'd really like a measurement. So we are looking for the last little bit that you could possibly detect. And that's the strong function of the brightness of the star because the telescopes have the size that they do that's not going to change for a while.

1:38:34Hopefully eventually it will. But it's going to be at least 10 years out. And so yes, we're often literally stuck in the noise because we can't make the measurement. So actually the record holder for the most iron poster only has an upper limit. We can't get enough data on this to actually pinpoint a measurement to then take it to our theory colleagues and say like, give me this little iron out of your first star. So it's a bit frustrating, but also super exciting at the same time. So let's go to both side of that spectrum. What's what's the most exciting discovery to you personally? Where is is there a moment you remember that you saw a piece of data and you kind of your heart skipped a bit.

1:39:17Yeah, yeah, of course. Is it is it H E 1327? That was that was definitely one of those moments. I wasn't actually present at the telescope, but we were sent a data immediately for my colleague. And we just looked at it and our eyes got really wide and was like, oh my god, this is just really what you think it is. So we had to run some numbers and it was. And these are magical little moments. The thing is, you know, often we have false positives. And so there is always this kind of period. And often it's, I don't know, 10, 15 minutes where you need to make some tests to kind of make the decision, is this really something I should keep observing?

1:40:03Now, is this really as good as I think or am I being fooled by something? Right? So actually, if you take a spectrum of a wide dwarf, a wide dwarf is the leftover core of a star like the sun that has gone extinct. And wide dwarfs have lost all their outer atmosphere. So it's just the hydrogen helium core. So they look like a metal porous star because that's only hydrogen helium left, right? But the hydrogen lines that you can see in the spectrum of stars and of the wide dwarfs are a little bit wider than normal. So you need to have a good eye just to check, you know, does this look a little bit wider than us?

1:40:40Is this a wide dwarf who's fooling me here, right? Because so it's like this moment is like, oh my god. It's just minutes of nervousness. Yes, yes. And sometimes, you know, it's it's a dud. And sometimes it's not. What's been what's been a big day? You remember heartbreak, like a painful low point. Is it all leading up to the first? Is it all body G 1327? Again, just the leading up to it. Or is there been like a, yeah, it has the brain like low points in the search? That's a good question. I mean, you know, it starts with mundane things as in like, you you want your telescope time, you travel there and the weather is completely cloudy.

1:41:23It rains. And you you had three nights, which is a lot and you go home empty handed. So that's definitely a low point. Probably not what you were thinking of. But there is a certain occupational hazard to it. Which requires a kind of resilient patient. Yeah. And you just got to learn to to live with it. Coming back to retake it on to actually, you know, that little dwarf galaxy. That was a run that we had and the weather was incredibly bad. And I had sent my student there. And I was at home and he calls me at 2 a .m. And he was like, I think I've served the wrong star. I'm so sorry. There is this line there, this European line.

1:42:07And it looks like a metal rich star. And I was like, it's cool. We all make mistakes. Send me the data. Send me that summary plot. And so I look at it, you know, I was like, super tired. It's like, I can't really tell. It doesn't look wrong. But I can't tell you right now that it's right either. So why don't you go to the next target. He calls me back in our later. And it looks just the same. What am I supposed to do? And then I joked, well, maybe we found an R process galaxy. Let's go to the next one. And the weather was degrading. And so to cut a long story short, we had to come. So he was observing the right stars.

1:42:57It was an R process galaxy. The first one we had ever discovered totally un, I mean, unprotected. We had no idea that this was a thing. I mean, you know, of course, we thought that, you know, such a thing might possibly exist because why not? Right? Nuchin Summer just happened somewhere. Crazy supernovae probably too. But we were not prepared in that moment to find this thing. And in the end, the weather was getting worse and worse. And we wanted to see how many app recessed stars are in this galaxy. So we managed by a hairline to observe the nine brightest stars, but the data quality was atrocious.

1:43:46And whether affects the data quality. Yes, absolutely, because these were really faint stars. And so we were really lucky by making a very tight strategy of getting the absolute bare minimum for all the stars. So we could at least take a very crude look. Is it a yay or a zine? We couldn't even say yes or no, just to get an idea because we needed to know why was that important because we could only observe this system again nine months later. So there's always a window of observation. Yes, it was setting. This was our chance. And it was going away with the clouds, you know. That was super high stakes.

1:44:30But we just made it. Really, it was almost impossible. And it was just the thing is, this is such a serendipitous moment in a serendipitous moment. The enhancement of these heavy elements was so strong that even in this really crappy data, we could still see the enhancement. Right, the absorption was so strong that stuck out of the noise, if that enhancement wouldn't have been as strong, we would not have been able to say anything because we wouldn't have been able to tell. But because it was so extreme, it lend us a hand despite the weather and all to say, yes, this is it. So that was quite the night.

1:45:16Luck, I mean, a lot of this is just luck. So that was the first our process galaxy discovered. Yes, I didn't sleep all that much. Do you have hoped? Are you excited about James Webb Space Telescope and other telescopes in the future that increased the resolution and the precision of what can be detected out there? Absolutely. Data WST is fantastic already. I am not planning to use it personally, although I think I'm on one or two observing proposals actually, because similar to what we already spoke about, we're interested in the same thing. We're just kind of looking at a different sides of the fence.

1:45:56Right. I have my old surviving stars and I concoct these little stories about what the earliest galaxies may have looked like, what the objects were that contributed energy and and elements and all these things. And my JWT colleagues, they try to detect some of these earliest photons from these earlier systems to look at the energetics and other things. What was there? How many these kinds of things? Right. So together, we're trying to explore this first billion years, but we do it in very complimentary ways. And so I'm very excited to see what they can come up with and how that helps me to inform my stories better and more comprehensively.

1:46:41What do you think is the future of the field of stellar archaeology? How much can we maybe what are the limits of our understanding of this first billion years of our universe? Well, obviously, lots of limitations in the sense that I always say, I have a metal poor star for any of your questions, because there are so many different kinds out there. And we still find new patterns sometimes, right? And there needs to be an explanation. The question is, is it ultimately just one quirky star? Is it two or three? Right? Is it a sample? Is it a population? So we haven't concluded that kind of work yet.

1:47:20So every metal poor star is a kind of data point that you can use to improve the quality of your model of how the evolution of the early universe. Yes. Yes. And I would say we're, we've made huge progress over the last 20 years. When I joined that field, it was in its infancy. And there was this serendipitous discovery of that first second generation star. And we have filled in the canvas a great deal since then. And this is what I have greatly enjoyed about doing so because there was so much discovery potential. And it's been, it's been dying down a little bit because of all the progress. It's gonna, it's gonna, it's on, on the app and coming again, because there's so many large spectroscopic surveys in the works now that will just provide a different level of data that we haven't had before.

1:48:13I'm sort of of these older generation. I have only very few colleagues. I've worked in small teams and I observe every single star myself. That you know, whatever I can, I do myself. I don't generally take other people's data, at least not certainly not in the end stage. And, and you know, I'm not a big data kind of person, although we all headed that way. I certainly use data from the Gaia astrometrics satellite for the kinematics, for example. But that's personally a new thing for me to, to use sort of big sky surveys that are available. So it's still very sort of hand -grown field, you know, where we do our individual observations.

1:48:59I have enjoyed that a lot, but that's about to change. So one start of time. Yes. I mean, there's power to that, to build up intuition of the early universe by looking one start of time. Yeah. And this is how you can really drill down on the questions that you have, right? Because you control what data you get. And otherwise you have the data that you have, right? You get what you get and you don't get upset. I don't like that. I'm a little bit snobby. I really like to formulate my questions, go to the telescope and then come what may. I will try to get it. And also develop the intuition of where the data can be relied upon and where it can't and all the different quirks of the data and all that kind of stuff.

1:49:39Yeah. Sometimes a lot is lost in the aggregation of the noisy data. Yeah, yeah, yeah. And that's always the danger if you have someone else's data that you just don't really understand the, you know, the limitations, completeness things, how certain things were set up. And, you know, you get out what you put in. So I'm really particular about that. And it certainly paid off for me. That's one of the main notions that I try to teach in my classes and to my students that you need to be able to formulate your quest question really well. Because otherwise you're going to get an answer to a different question.

1:50:17But you won't notice that it had that the goalposts has shifted in the meantime, right? So your interpretation can only be as good as the question. If you need to change your question, that's cool. Do it. But then, you know, it needs to pair up with your interpretation again. And so knowing really being in the know about every step of what happens, that relates to quality results, I think. That's why I have sometimes little trouble with sort of big data and statistical analysis. Yes, on average, that's true. I'm not debating that. But I'm the kind of person I like to look at the outliers, so not the bulk, but, you know, the special ones.

1:50:57And they just need to be treated in a different way. And there needs to be an acknowledgement of that different ways for different things. So big data can look at divorce rates. And perhaps you and I are more interested in the individual love stories. Yes. That works for me. So I don't know if it's possible to say, but what do you think is the big discoveries that are waiting? Is it on the different dynamics of the yield, the common narrative, the common story of how some of these metal poor stars are formed? Is it where the discoveries feel that you think will come? I think the individual discoveries, I actually, we've made most of those, certainly through individual stars, finding yet another second generation size incredibly important for me, but isn't really going to move the needle, finding 50 of them or 100 of them, that would move the needle, but that's in order or two magnitudes up.

1:52:05And new search techniques and new surveys may enable that, but would you still call that a discovery? So that's just a scale. Yes. So I think about it more, like literally of the puzzle, let's say you have a thousand piece puzzle and you know, you have 900 pieces in there. If you're a person like me, I want to get to the last ones. I'm not going to leave it. It's like, okay, I see broadly what this is going to look like, right? I'm done now. No, I want to get to the last one. So is the picture globally going to change? No. Are we going to figure out all the details and how it really works? Yes.

1:52:46Right? So really careful detail map out the ancient, the ancient stars of our universe. Yeah. Because I think that's what many of our scientists are a little bit detailed obsessed, but I think that's our job too, right? To really kind of make it airtight. To really walk away saying, I fully understand this. Not just broadly, but you know, I really know we really know now. And so more and more of that is going to happen. And so I think this is probably true across astronomy. These individual ten sigma discoveries become less and less. If they were easy, we would have made them already, right? Which means we have made many of them.

1:53:35But really filling in the details is the next sort of level of discovery. Maybe we need to find a new word for that. The hopes and expectations that go along with the word discovery are so enormous. We may not always be able to live up to that. But it doesn't mean that we're not finding out new things. It's just a different kind of quality because the questions have shifted. You close one door, suddenly there are ten new open doors that we want to explore and march through. And that's the finding these last puzzle pieces here in there that we remake it airtight. And so there's a lot of value and a lot of power and to the discovery in the big picture of our universe and in the details.

1:54:23So both of them. We need both. Absolutely. Perhaps drifting into the philosophical. Let me ask about the big bang as we kind of encroach onto it. So your work is kind of taking steps back through time in a weird way. Do you think we'll get to deeper and deeper understand the really really early days of the big bang? And the philosophical question, do you think we'll be able to understand what was before the big bang or why the big bang happened? Do you think about that stuff? Not with stars. For better or for worse. Because stars only probe the time when they were formed. And the big bang is surely before then.

1:55:10I mean, I often talk to my students about the difference between math and physics. Let me give you an example. We talked earlier about 1815 -23 and you know, I was happy to share with you that I met a thorium in uranium but I actually didn't quite close that loop. So we did this to try to attempt to calculate an age for these stars. But they rely on us knowing how the R process works, how these elements are created, where it happens, and then how those elements get dispersed into the gas and end up in the next generation star. So quite a few question marks. So that's how we got to the age of 13 .2 billion years.

1:55:52This is probably not accurate, but this is the best calculation we could do. And the reason why I'm bringing this up is that that was actually the average of multiple elemental ratios that each gave a certain age. And then we average that because for better or for worse, this is the best we can do. So some of these numbers said, oh, this star is 15 billion years old. And then others said, oh, this is 10 billion years old. And so I often use that in my class to say, like, what's the good news and what's the bad news here? Some ratios say 15, something 10, right? Is 15 correct? And then I asked them and some people will say something.

1:56:38And so the thing here is that it's an absolutely correct calculation given the mathematical and physical model that we constructed. But does it make sense? No, it doesn't. If we believe the universe is 13 .8 billion years old, 15 is ridiculous. Yet it is correct. Isn't that interesting? Correct. From a mathematical perspective. It is not incorrect because this is what I calculated. Nobody made a mistake. Now, we can question whether that's a good model. But that's that's a separate issue. So you're saying physicists are much closer to truth than mathematicians? Well, it depends. Sometimes yes and sometimes no, right?

1:57:18So what our job as physicists is to take the mathematical model, calculate our numbers, and then ask the question, does this make sense? Right? Now, in the case of 15, it doesn't, but we took the average anyway because that was the best we could do. Right? So, all right, let's put that aside. Let's apply the same sort of thinking to the Big Bang, right? Math can tell us things that we as physicists cannot grasp because it doesn't make sense to us. Now, in the case of the Big Bang, that's the special case because we don't actually know what's supposed to make sense. And this is where things get interesting.

1:57:58But this is where math will ultimately be the winner, because we can no longer say this makes sense or this doesn't make sense because the physics is broken down. But math breaks down too in the singularity of things. Well, depending on who you ask. It's sure. This is the current question, right? How far, how much further can we push math, let's say, to the front of the Big Bang, if there is such a thing? What's the front in the back? What's the front? The front is the before the Big Bang. Oh, before the Big Bang, the front. Okay. So, why, how? The all the doorways in the entrance. So, how far can we let the math go before that stops to make sense, right?

1:58:41And I don't know what the answer is to that, but it's really cool that because math doesn't have, it's not limited by our physical nature. It can probably go a little bit further than the physics. Yeah. Right. And math can go into more dimensions than four dimensions comfortably. And it's, it's judgment free because it just calculates things on its own. Whereas as physicists, we're so judgmental. Yeah. This makes sense. This doesn't make sense. It doesn't get any worse. It's such a beautiful dance. It's such a, it's so amazing that through this dance, you get to explore the origin of the universe.

1:59:20Like, this isn't the Big Bang, just blow your mind that this thing is just started from a point. Yeah. And now we're here. Yeah. Yeah. Yeah. I had a gym in helium. And then all the stuff you're studying, I mean, this, this, this evolution of chemistry created humans. And we're here talking. And there's a lot more to the story. It's amazing. Yeah. Yeah. Yeah. And this kind of march that you're doing is observing data. And is there, you're looking at old light, an old data, but only a few thousand years, right? Just a few thousand years. That's, that's the difference between me and my J .W .T. colleagues.

2:00:07Their objects, that light has traveled 13 billion years or whatever it was to us and they're observing that now. My light has only traveled a few thousand years. It's, it's nothing. So whatever you observe now is likely still going on. Yes. These stars are alive and kicking and having a blast. Thousand years. Just a few thousand years. It all it takes. If we can travel close to the speed of light, yeah, maybe we can reach out there. We wouldn't have any planets around those stars though. So that's, is that a definitive intuition? Well, what are planets made of? Elements, right? To take the earth as all heavy elements, right?

2:00:47The universe needed to reach a certain stage first to have produced enough of all these elements to actually make a planet. So on average, you got, so okay, right? So that took quite a few billion years. So they're not going to have a mechanism for forming planets. You could have visitors probably, but the kinematics of that are weird, are unlikely. Yeah, I would say so. Okay. So they're interesting in that they reveal the early chemical evolution of the universe. Yes. Not that they're, that could be good vacation spots, but not well, they're not going to be like a worm. No, no, no planet islands to go to chill.

2:01:29In your book, you highlight the major contributions in the field by many women. Some of these women were not as you describe them immediately credited for their discoveries. So for me, from from computer science perspective, the story also tells Harvard computers, who were these women and what can you just say about the nature of science and humanity? Discovering things is in is part of the human nature, right? And so it has happened for the longest time, not just by men, but also by many women. The field of stellar astronomy, which is my field, has particularly benefited from many discoveries made by women.

2:02:16You mentioned the Harvard computers, that's a term used for women who worked about a hundred years ago at the Harvard College Observatory. And they were hired for their low wages and willingness to do diligent and patient work to comb through the big data of the day. So the observatory director, they were carrying out large sky surveys at the time and they needed that data needed to be processed and looked at and analyzed. And so many women or several dozens, or one or two dozen women over over the years, were higher to do this work. And in the process, because they were looking at the actual data and they were smart, even though they had often no formal education, they made a lot of discoveries simply by being in tune with what they were doing.

2:03:21So they were on robots, the term computer would perhaps let on, lead on. So any jump cannon, classified thousands and thousands of spectra and found out that you can, you know, stars have different temperatures and their spectra look according. We still use the classification sequence today. Cecilia Penda Poshkin, later on in I think 1925, was one of the first women to obtain a PhD in stellar astronomy and she figured out she calculated that the sun is mostly made of hydrogen and helium. That seems normal to many of us these days, but at the time, it was thought that celestial objects are made of the same thing as the earth.

2:04:22That's a gutsy, amazing discovery. Yes. It was later termed the most important thesis of humankind or something like that. What a revelation to realize that stars are made of hydrogen and helium, right? And this was exactly the time when people figured out why stars are shining, namely because of nuclear fusion and that it's protons and, you know, the tunneling effect that leads to do the actual fusion. Otherwise, you know, the protons repulse each other. They don't come together. And so what an incredible time it was back then. And so stars and nuclear physics were very closely related. And it remains that now it's called nuclear astrophysics.

2:05:07And so many women had many contributions to that.

2:05:13Of course, radium and polonium, Lisa Maithna discovered nuclear fusion. That is the basis for understanding the R process. This is exactly what happens in the R process. You know, the heavy nuclei, let's say uranium, if you bombarded with a neutron, we talked at length about it. It will decay. It will fusion, it will split into barium and krypton, let's say. So two lighter elements. That's exactly what we observe. I have always a higher abundance of barium than the heavier elements because of this fusion cycling that she calculated in 1938, 1939. So many, many contributions. And it's just so remarkable.

2:06:11If you just take that body of work, that changed how we do things, how we see the universe, how we understand things has led to so many subsequent discoveries. Good ones and bad. Well, we did all of it is taken together. That's progress. It's, it's, it's science is what it is. We have to decide what we do with that knowledge, right? We can always use things for go to for bad. That's that's part of the human endeavor as well. And also part of the human endeavor and the human nature is the issues with corruption and credit assignment and all these kinds of things that are that make this whole ride so damn interesting.

2:06:55What's right and wrong and about the nature of good and evil. And that seems to surface itself in all kinds of places all the time. Yes, yes, Lisa Maiden was nominated for the Nobel Prize 40 times more than that even. It's amazing. She holds the record for that. She never received it. Case in point. Yeah, and of course, the Nobel Prize is as complex as he's one is the credit assignment, but two, even an astronomy sort of assigning credit to a handful of folks once so many more contributed as a complicated story also. Yes, very complex. Okay, sorry for the romantic question, but what to use the most beautiful idea in astronomy in stellar astronomy?

2:07:42Well, so early on, you know, when when I was in high school, I was thinking like, okay, well, what, what, what do I want to do when I'm growing when I grow up, right? I know I wanted to do astronomy, but I was a little bit torn because my interests were definitely stars, stellar astronomy, but also chemistry. I always had a fascination about the elements. So Marie Kiri was was a big role model. My friend actually made a beautiful, producer beautiful movie about the discovery of of of of the elements, this is a theater play, but digitized, where when I thought I could actually kind of relive the sort of discovery moment that that Marie Kiri had, it sent Chirros down my spine.

2:08:29It was fantastic. I mean, this is this is the kind of thing that that I wanted to experience. But yeah, so nuclear physics and element creation information was really interesting to me chemistry, the element stars and all of that. And I was like, I don't know if I ever find something that combines all of these things. And then I ended up in Australia and I met this this person and he was working on old stars. And as I was sitting in his talk, hearing about this for the first time, it kind of it clicked all over my head and was like, oh my god, it all fell in place because we can use these old stars to study the elements to learn how they're formed.

2:09:14We can get these clean signatures that help us inform the nuclear synthesis processes, you know, and I know of course I need to know a lot about stars too. So it's like all together and that that was sort of a moment of magic. And then the fact that I have now done that for 20 years, it's just like I won the lottery. It all clicked into place. And so in some sense, it's an ongoing love story for me if I could say it like that, where you know, I found my stars, my thing. And I'm fortunate enough to be able to keep doing that. And I'm happy to see where where it will take me, you know, it's an evolution as with every relationship.

2:10:00You have to, if you don't march forward, you move backwards. I'm not interested moving backwards. So I'm I'm letting the field and the discoveries and the findings lead me to, you know, and I'm often I'm it's it's not hard for me to follow sort of my hunches and sometimes even at the tellers, Cobb and snack, hmm, let's take a look at this one. I have a good feeling. And then usually something good or you know, not bad. Popps pops out at the end. And I, I really like that. A, that I have the freedom to do that that I'm allowed to follow my hunches. Too many people I think are sort of boxed in with their job or their life that they don't have that kind of freedom that that's really important to me.

2:10:48And I certainly try to make use of that. I also try to teach that to others to trust them to learn, you know, you need to learn your things, but then you need to also trust that knowledge and then you have a grasp on it, right? You get out what you put in. And being able to contribute in meaningful ways to our knowledge about our cosmic ancestry or cosmic history, that's that's a wonderful thing. And in this way, your personal love story with the stars of all's, what advice you've already spoken to it a little bit, but what advice would you give to young people that are trying to find the same kind of love story in their career in their life?

2:11:34It seems increasing the hard for folks to to find that. Sometimes I feel that, you know, young people have all the opportunities these days and that's that's wonderful. But it's almost like that leads to some, what's the right word, they're, they're a little bit of tired of too, too tired to make all the decisions because at some point you need to put your eggs in a basket and you need to be okay with that. We can't do all the things even though we're often told you can be president too. And I think that's really important to convey. But at the end of the day, we can only have sort of one job or one type of profession.

2:12:15I'm not saying, you know, you need to be locked in, but it's hard to change 180 degrees. And so lots of people I think are often afraid to to really dig in at least for some time and get the hands real dirty and really learned from the bottom up on one thing on one thing because they're afraid they're missing out on on 99 other things. But life is a little bit missing out on 99 other things because we only have 24 hours in a day. I I have that feeling very often. There are so many things I would like to do. Many things I would like to try to be good at. Sometimes I wish I had a different job, you know, because other interests too, but I realized, okay, I can only do one thing.

2:13:04So I have no regrets. But this is this is a general feeling that I think I would think most of us have. But if it lets if it stops you from really digging drilling down on one thing to become an expert and one thing to become really good at one thing that you call your own, then that it just makes a difficult. And so a fulfilling life is in part likely to be discovered in a singular pursuit of a thing of one thing. Well, yeah, for at least for a time. Yeah, for some time with your with your heart and your hands, because I think most people long to own something. You know, we all I think want to leave some legacy of some sorts, you know, for our children, for humanity, for this planet.

2:13:56And I think it's really important for young people to strive for that and not lose sight or trade that for all the opportunities because an opportunity is nothing if you don't do anything. You need to you need to do something at the end of the day. So I chat with lots of people about this and I often start by just saying, Hey, tell me what you don't like. Because it's often much easier to narrow down, narrow down, let out what what's not on your plate. And then this way we get a little bit closer. And then I was like, well, why don't you take a risk and just sign up for something for three months?

2:14:35But that's what it feels like. That's what it feels like. And it is that is a risk. Commitment is a risk. Yes. Because it's your basically sacrificing all the other possible options. But then I guess you have to trust the magic you noticed in that thing. Yes. You notice one thing just stick with it. And then and then maybe there's something there. Right. Right. And and this moment of kind of feeling it in your entire body and mind that this is the right thing, you know, getting there is is probably really hard. But if you don't try, you won't find out. The hard stuff is the fun stuff. That's also another thing you find out.

2:15:11And then there's that. Yes. Somehow it doesn't make sense. You also mentioned that you've taken a little stroll into the artistic representation of yourself. Can you can you speak to that for a little bit? Yes. Well, I already just mentioned. And sometimes I wish I had more time to do other things. So I find little little sideways, I guess, to to pursue things that I like besides astronomy or at least I try to find connections. And so some years ago I again with the help of my friend who made this Marie Curie movie, she and I wrote a one woman play where I actually portray Lisa Maidna who was an Austrian German physicist, Nuclea physicist from Germany.

2:16:04So I have the right accent for that. And we wrote this play about this moment of discovery of Nuclea Fischen. Again, this is an absolutely critical piece that explains my work today. And we all stand on the shoulder of giants. She was one of those giants. And in some ways it's it's of course a way for me to acknowledge other people's work that have come before me. It's a wonderful way to highlight the contribution by a prominent woman. And the way I do it is it's a 25 minute play in costume where I relive for people the moment of discovery. Then I turn into myself and then I give a 30 minute presentation on the our process and the creation of heavy elements because the audience can now perfectly understand that the public audience given the historic backdrop of this discovery that they just lived through my presentation.

2:17:17And it's it's a wonderful compliment that almost spends 100 years from one woman to the next passing on the torch. And you know when we write up our results in let's say you know magazines like Nature and Science it's always about the result on the golden platter perfectly prepared. It's the discovery is never described only ever the results. You ask me beforehand right what does it feel to be at the telescope in this moment right? I'm happy to talk about this but it's nowhere written never nobody nobody really talks about it. And so having a form of you know theater of the arts to bring this this exciting moment that that is what we all want to experience as scientists to a wider audience is so profound and so rewarding and they all love it because everyone can understand a moment of discovery.

2:18:19I was looking for something and then I found it. It's like you misplaced cockies right? Or love. Yes yes. Everyone can understand. The glories experiences yes. The implications and the findings that is much harder to understand for the for anyone. This is where the scientists work truly lies. This is our job but the moment of discovery is easy and it's beautiful and it needs to be said. And so taking my audience on this journey what is the perils what are my worries and then oh here is the moment of discovery. Let me tell you about it. It profoundly transformed me and here here's how it went right?

2:19:05It's so good. And art is a way to reveal this fundamental human side of science. Yes it's the problem with science is that's people doing it. That's also the problem but that's also what makes it beautiful right? Humans are fascinating and they were able to come up with these ideas through all the struggle, through all the hardship, through all the hope, through all the search. And so the art is a great way to portray that and to broadcast that right? I think this is how the audience really should be interacting with scientists much less about the findings but really more about this yearning for answers right?

2:19:45I need to find these cockies. I need I need it because I need to go right? It's like now now. And then oh god here it is. Now I can go my my Maryways. It's so relatable. We just need to find more and better ways to do that. So I hope to turn this into also a digitized version at some point to again make it more accessible. I hope so too. So far I'm just doing it in person but it's I would love it. I think a lot of people would love to see it. So I hope you do just that. Let me ask you a big ridiculous question. You look up at the stars. You look up at the early early early stars. So let me ask the big question that we humans often ask and struggle to answer.

2:20:31What's the meaning of this whole thing? Why why are we here? We talked about you know the biological evolution requires the chemical evolution for all of this to kind of play out and carbon play this important role. And you know in some sense we're just a consequence of all of these things being the way they are right? So maybe this is just where we are supposed to be because you know the the last of physics sort of work the way they do. And we talked much about the variety of of everything really in certainly you know from over here to over there. And things in the vicinity of where the Sun and the solar system formed they were the way they were and life maybe wasn't necessary consequence of that.

2:21:23In some sense I like to believe that because then it becomes reproducible and we can apply that same argument elsewhere. If it's total chance right that makes it harder and that's not not truly satisfying to to a scientist. So it's a it's a consequence of psychological evolution which is a consequence of biological evolution which is a consequence of chemical evolution consequence of physical evolution and whatever whatever disciplines it's turtles on top of turtles. Turtles all the way down yes. I yeah you will have studied some of the most ancient turtles. Yes very bottom of the thing. That's right.

2:22:02They live for quite a while. Yes they do. Well thank you for your incredible work. Thank you for highlighting both the human side and the deep scientific side. It's just I'm a huge fan of you work and thank you for everything you do. I thank you for talking today. This is awesome. Of course it was wonderful. Thank you. Thanks for listening to this conversation with Adam for Bell to support the spot gas please check out our sponsors in the description. And now let me leave you with some words from Douglas Adams in Hitchhike's Guide to the Galaxy. Far out in the uncharted back waters of the unfashionable end of the western sprawl arm of the galaxy lies a small unregarded yellow sun orbiting this at a distance of roughly 92 million miles is an utterly insignificant little blue queen planet whose ape descendant life forms I saw amazingly primitive that they still think that real watches are pretty neat idea.

2:23:01Thank you for listening. I hope to see you next time.