Anna Frebel: Origin and Evolution of the Universe, Galaxies, and Stars | Lex Fridman Podcast #378
- I would run outside and just lay on the ground
under the southern Milky Way; beautiful, right, up there. And I would just lay
there like the snow angel and just kind of let my thoughts sort of pass through my brain. And this is when I
personally have the feeling that I'm apart of it, I belong here, rather than feeling kind of small. Yes, I'm small, but there are many other small things. And lots of small things
make one big whole. - The following is a
conversation with Anna Frebel, an astrophysicist at MIT studying the oldest stars
in the Milky Way galaxy in order to understand the chemical and physical conditions
of the early universe and how from that our
galaxy formed and evolved to what it is today, the place we humans call home. This is the "Lex Fridman
Podcast"; to support it, please check out our
sponsors in the description. And now, dear friends, here's Anna Frebel. Let's go back to the early days. What did the formation of the
Milky Way galaxy look like? Or maybe we wanna start even before that. What did the formation of
the universe look like? - Well, we, scientists,
believe there was the Big Bang, some big beginning. (chuckles) But what is important for my work, and I think that's what
we're going to talk about, is what kind of elements
were present at that time. So the Big Bang left a universe behind that was made of just hydrogen helium and tiny little sprinkles of lithium, and that was pretty much it. And, as it turns out, it's actually quite hard to make stars or any structure from
that, that very hot gas. And so the very first stars that formed prior to any galaxies were
very massive stars, big stars, 100 times the mass of the sun, and they were made from
just hydrogen and helium. So big stars explode pretty fast, after a few million years only. That's very short on cosmic time scales. And in their explosions, they provided the first heavier
elements to the universe because, in their course, all stars fuse lighter elements like hydrogen and helium
into heavier ones, and then that goes all the way up to iron. And then all that material gets ejected in these massive supernova explosions. And that marked a really, really important
transition in the universe. Because after that first explosion, it was no longer chemically pristine. And that set the stage for
everything else to happen, including us here talking today. (laughs) - So what do you mean by pristine? So there's a whole complex soup of elements now as opposed to just hydrogen helium and a little bit of lithium. - Yeah, so after the Big Bang,
just hydrogen and helium. We don't really need to
talk too much about lithium because the amount was so small. And after these very first
stars formed and exploded, the heavier elements like
carbon, oxygen, magnesium, iron, all of that stuff was suddenly
present in the gas clouds in tiny amounts only,
only very tiny amounts. But that actually helped, especially the carbon and the oxygen, to make the gas cool. These atoms are more
complicated than hydrogen, that's just a proton, and so it has cooling properties, can send out photons
outside of the gas cloud so the gas can cool. And when you have gas that
gets colder and colder, you can make small and smaller stars, so you can fragment it and clump it and turn it into stars like the sun. And the cool thing about that is that when you have
small stars like the sun, they have a really long lifetime. So those first low-mass
stars that formed back then are still observable today. That is actually what I do. I try to find these early survivors because they tell us what the
gas looked like back then. They have preserved that composition of these early gas cloud, the,
the chemical compositions, until today. So I don't need to look
very far into the universe to study all the beginnings, I can just chemically
analyze the oldest stars. And it's like unpacking everything
that happened back then. It's very exciting. - So to just reiterate. So in the very early days, in
the first few million years, there was giant stars that's
mostly hydrogen and helium. And then they exploded in
these supernova explosions and then they made these clumps- - [Anna] Yeah, so the first stars- - Not pristine. Not pristine clumps? - Yeah, pretty much.
- Fun. - So it took a few hundred million years for the first stars to emerge and then they exploded
after a few million years. Kaboom. And then it's like I always
consider the universe like a, you know, a nice soup. And then these first supernova explosions kind of provided the salt, you know, just a little sprinkle
of heavier elements, and that made it really tasty. (chuckles) It just changed it completely, right? And that changed the physics of the gas. So that meant that these gas
clouds that were, you know, surrounding the former first stars, they could now cool down and clump and form the next generation of stars that now included also little stars. And, as I just mentioned, the small stars have these
really long lifetimes. The sun has a lifetime
of 10 billion years. Any star that is even less massive will have an even longer lifetime. So that gives us a chance to
still observe some of the stars that formed back then. So we are testing the conditions, the chemical and physical conditions, of the early universe even
before the galaxy formed. - So what's the timeline
that we're talking about? What is the age of the universe? And what is the earliest
time we got those salty, delicious soup, clump soups
with heavier elements? - Well, the universe is
13.8 billion years old. - Allegedly, yeah. Is it? So-
- Yes. - Okay, 13.8-
- Well, you know, when I was in high school, the universe was 20 billion years old. - [Lex] Oh, yeah? So the estimate-
- Things have changed. - Do you think that estimate will evolve in interesting ways or no? Is it pretty stable at this point?
- I think we have have mostly converged, yes, because the techniques
are very different now, much more precise. The whole business of precision cosmology by mapping out the cosmic
microwave background, you know, that's a marvelous feat. Maybe, you know, the digits will still
move around a little bit, but that's all right. - Plus the gravitational
waves and all that, so all the different sources of data kind of mapping out this detailed picture of the early universe. Yeah.
- Totally. And so we think the earliest
little stars formed, I don't know, maybe 1/2 billion years
after the Big Bang, right? Again, a few hundred million years for the first stars to emerge and then, you know, took some time, so give or take 1/2 billion years. And that was the time when sort of the very
first protogalaxies formed, early stellar structures, stellar systems, from which the Milky Way
eventually formed, right? So it was... The Milky Way was probably
a slightly bigger one. And we know today that
galaxies grow hierarchically, which means the eat
their smaller neighbors. So if you are the bigger one and have a few friends around, you're just gonna eat them, absorb them, and then you grow bigger. And so all these little
early stars, you know, kind of came into the Milky Way through that kind of process, and that's why we find them in the outer parts of the galaxy today, because they're just kind of (indistinct) and just left there since. - So the old stuff is on
the outskirts of the galaxy and the new stuff is closer to the middle? Is there-
- Broadly speaking. - Okay.
- Yes, yes. - So that's where you would look for it. So maybe just a step back. Like, what is a galaxy? What is a protogalaxy? - I love that question. So the galaxy is a huge assembly of stars. The Milky Way contains something like 200 to 400 billion stars. And most of the material and
the stars are in the disc. And when we look at the night sky, what we see as the Milky
Way band on the sky, that is actually the inner, the next inner spiral arm, because we actually live
in a spiral disc galaxy. The Milky Way is spiral disc galaxy. And we are looking... Actually it depends a little bit. In the Northern Hemisphere, we're looking out of the galaxy, so we are seeing the
next outer spiral arm. And as you can imagine, there's only dark space behind that. So we don't see it all
that nice on the sky. But if you travel to
the Southern Hemisphere, let's say South America, you see the Milky Way and it
looks so different on the sky because that's the next inner spiral arm, and that's back lit by
the galactic center. The galactic center is a
very big, puffy, you know, region of gas, there's
a lot of star formation. The galactic party is happening there, so it's very bright and it makes for this
very beautiful Milky Way on the night sky that we see. So actually if you ever get
the chance to experience that, I encourage you to almost
like close your eyes while seeing this and
imagining that you are sitting in this kind of disc, in this pancake, and you're just kind of
looking right into it. And you can really feel
that we are in this 2D disc. And then you can imagine that
there's a top and a bottom and that we're really part of the galaxy. You can really experience that. We're not just lost in space somewhere, but we're really a part of it. And, you know, knowing a little bit about the structure of the Milky Way really helps. - Do you feel small when
you think about that, when you look on that spiral on the inside of the Milky Way and then you look out to the outside? Like, how are we supposed to feel? - I don't know. I don't feel small, necessarily. I feel in awe and I feel I'm a part of it because I can really feel
that I'm a part of it. I think for many people
they think like, oh, there's just the planet
and then there's nothing, and that's almost a little bit sad. But that's really not the case, right, because there's so much more. And I really like to imagine, "Wow, I'm sitting in this
big galactic merry-go-round and we're going around the center." And I can see the center above me, right? And I can almost feel like we're going, going there. (chuckles) Of course we can't really feel that, but the sun does circle
the galactic center. - But there's a kind of sadness to... Like looking at pictures
of a nice vacation place, all we get is that light, an old light. Do you feel, like, sad
that we don't get to travel or you and I will not get to travel there and maybe humans will
never get to travel there? - Yeah, I always wanted
to travel into space and see the Earth and
other things from up there. There's certainly that. But I don't know. It's also okay to just
be at our vantage point and see it from here. - With the sensors, with
the telescopes that we have, and explore the possibility. I mean, there is a kind of
wonder to the mystery of it all, what's out there, what interesting things that
we can't possibly imagine. You know, there could be all
kinds of life forms, bacteria, all this kind of stuff. I tend to believe that... You know, it depends on the day. I tend to believe there's just a lot of
very primitive organisms just spread out throughout, and they build their little things, like bacteria-type organisms; and just to think what
kind of worlds there are. 'Cause they're probably really
creative living organisms 'cause the conditions... I guess the question
I'm wondering to myself when I look out there to the stars, how different are the conditions on the different planets
that orbit those stars? - It will definitely be very different. I mean, the variety out there is is huge. We know now that... I think it's about every other
star has at least one planet. I already mentioned the
number of stars in the galaxy. I mean, you know, it's a huge
number of planets out there. So who knows what that looks like? All we know is that there
is a lot of variety. We don't quite yet
understand what drives that, what governs that, why that is the case. Why is it not all one size fits all? - Oh, you mean the dynamics
of planet formation, like exoplanet formation
or star formation, the whole shebang?
- All of it, all of it. Star formation remains
a much researched topic. We kind of, we definitely
know that it works because all the stars are
there, same for the planets, but the details are so
varied per gas cloud, right? It's very hard to come up with
very detailed prescriptions. Broadly, we have figured it out. You need a gas cloud, you need to cool it, something clumps and fragments and somehow it makes a star
with planets or without. - But the dynamics of the clumping process is not fully understood. - No, no. And the local conditions
are so varied, right? I mean, it's the same with, you know, all people look like people, but individually we look very different. - So even the subtle diversity
of the formation process creates all kinds of fun differences.
- Yes. So we just don't know how this turned out in an individual case, and it's kind of hard
to figure it all out. And to take a look, certainly
with planets, right, the chance to ever actually
take a picture of a planet is minuscule because they don't shine, so they're really dark. (laughs) So I'd say there's a lot
of possibility out there, but we have to be a little
bit more patient before we- - Or come up with technologies where patience becomes less necessary by extending our lifetimes or increasing the speed of space travel, all the kind of stuff. Humans are pretty, pretty intelligent, they're pretty-
- Sometimes, yeah. - Sometimes sometimes. For the most part, I hope, on the optimistic days. Well, maybe just to linger
on the, what a galaxy is. What should we know about our
understanding of black holes and their formation? Is that an important thing to understand in the formation of a galaxy? Like, so all the orbiting, all the spiraling that's going on, how important is that to understand? - All of the above. That's what makes astronomy really hard but also really interesting, right? No day is like another because
we always find something new. I wanna come back to the
idea of the protogalaxy because that actually
matches or, you know, relates to the black hole formation. So most large, well, pretty much all large galaxies have a supermassive
black hole in the center. And we don't actually know, we don't really know where they come from. Again, we know that they're there, but how do we get there? So if we go back to the
early universe, right? We had a little galaxy that just sort of, you know, I don't know, had some small number of stars. It was the first
gravitationally bound structure that was held together by dark matter, because dark matter actually
kind of structured up, you know, first before
the luminous matter could because that's what dark
matter kind of does, and it started to hold gas and
then stars sort of together in these first very shallow, what we call potential wells, so these gravitationally bound systems. And then the mice grew from
absorbing neighboring, smaller, even smaller systems. And somewhere in that process there must have been a seed for one of these supermassive black holes. And I'm not actually sure
that it's clear right now kind of what was there first, the supermassive black hole or the galaxy. So lots of people are
trying to study that. And of course the black hole
wasn't as massive back then as it is these days, but it's a big area of research. And the new James Webb,
the JWST, the telescope, the infrared telescope in
space, is working on... Many people are working on that to figure out exactly what happened. And there are some surprising results that we really don't
understand right now, so... - So to solve the chicken
or the egg problem of: Do you need the supermassive
black hole to form a galaxy or does the galaxy naturally create the
supermassive black hole? - Yeah. Yeah. I mean, I think to some
degree we can answer that because there are lots of
little dwarf galaxies out there. You know, the Milky Way remains surrounded by many dozens of small dwarf galaxies; I have studied a bunch of them. And to the extent that we can tell, they do not contain black holes. So there certainly were
gravitationally bound structures, so either you can call them protogalaxies or dwarf galaxies or first galaxies, they were definitely there. But there must have been bigger things, like the proto Milky Way, where something was different, right, what made them more
massive so that, you know, they would gravitationally
attract these smaller systems to integrate them. So we'll have to see. - How do we look into that, into the dynamics of the formation, the evolution of the protogalaxies? Is it possible? Did they shine? I mean, what are the set of data that we can possibly look at? So we've got gravitational waves, which is really insane that
we can even detect those. There's light. What else can we- - So that would fall into the category of observational cosmology. And the JWST is the prime
telescope right now to... And it promises big steps forward. This is in its early days
because it's only been online like a year or so. But that collects the infrared
light from the furthest, like literally protogalaxies, earliest galaxies that light has traveled some 13 billion years to us, and they're observing these
faint little blobs. (laughs) And folks are trying to, you
know, again, study the early, the onset of these early
supermassive black holes, how they shape galaxies. So they're seeing that
they were there, you know, surrounded by already bigger galaxies. Ideally I'd like for my colleagues to push a little bit further, hopefully that will
eventually happen. (laughs) - [Lex] In terms of looking towards the older and older ones? - Yeah. Yeah. And more and more sort of primitive in terms of the structure. But, of course, as you can imagine, if you make your system
smaller and smaller, it becomes dimmer and dimmer and it's further and further away. So we're reaching the end of the line from a technical
perspective pretty quickly. - But it's dimmer and dimmer
means older and older? - Yes, in a sense, because
it all started really small. All right? - [Lex] Because it's smaller and smaller, which correlates to older and older. - In that phase of the universe, it would, otherwise it doesn't, yeah. - Just to take a small
tangent about black holes, and, you know, because you do quite a bit
of observational cosmology and maybe experimental astrophysics. What's the difference to you between theoretical
physics and experimental? So there's a lot of really
interesting explorations about paradoxes around black holes and all this kind of stuff, about black holes destroying information. Do those worlds intermix to you especially when you
step away from your work and kind of think about
the mystery of it all? - Well, at first glance there
isn't actually much crosstalk. Personally, I mostly observe stars. So I don't usually actually think too much about black holes. - And stars is a fundamentally kinda chemical physical
phenomena that doesn't- - That's right. The physics
is kind of different. It's not extreme. - I mean, you know, you could consider a nuclear fusion sort of be perhaps extreme. You need to tunnel. There's some interesting physics there, but it's a different flavor. I don't do these kinds of
calculations myself either. I very much like to talk
with my theory colleagues about these things, though, because I find there's always
an interesting intersection. And often it's just... I've written a number of papers with colleagues who do like
simulations about galaxies. And so they're not quite as
far removed as, let's say, the black hole, you know,
pen-and-paper folks. But even in those cases, we had the same interests
in the same topics, but it was almost like we were speaking two different languages. And we weren't even that
far removed, you know, both astronomers and all. And it was really interesting
just to take the time and really try to talk
to each other. (chuckles) And it's amazing how hard that is. You know, even amongst scientists, we already have trouble
talking to each other. Imagine how hard it's to
talk to non-scientists and other people to try, you know, to... We are all interested in the same things as humans at the end of the day, right? But everyone has sort of
a different angle about it and different questions and
way of formulating things. And sometimes it really
takes a while to converge and to get, you know,
to the common ground. But if you take the time, it's so interesting to
participate in that process. And it feels so good
in the end to say like, "Yes, we tackled this together," right? "We overcame our differences, not so much in opinion but just in expressing
ourselves about this and how we go about solving a problem." And these were some of my
most successful papers, and I certainly enjoyed them the most. - And it could also
lead to big discoveries. I mean, there's a... I think you put it really well in saying that we're all kind of studying the same kind of mysteries and problems. I mean, I see this in the space
of artificial intelligence. You have a community, maybe
it seems very far away, artificial intelligence and neuroscience. You know, you would think
that they're studying very different things. But one is trying to
engineer intelligence, and in so doing trying to
understand intelligence. And the other is trying
to understand intelligence and cognition in the human mind. And they're just doing it
from a different set of data, different set of backgrounds, and the researchers that
do that kind of work. And probably the same is true in observational cosmology and simulation. So it's like a fundamentally
different approach to understanding the universe. For simulation: "Let me use the things I know to create a bunch of
parameters and create some, just play with it, play
with the universe, play God, create a bunch of universes and see in a way that
matches experimental data." It's a fun, it's like playing
Sims but at the cosmic level. - [Anna] Yes, yes. (Laughs) - And then probably the set
of terminology used there is very different. And maybe you're allowed
to break the rules a little bit more. Let's have... You know, yeah... It's like the Drake equation. Yeah, you don't really know. You kind of come up with a
bunch of values here and there and just see how it
evolves and, from that, kind of intuit the
different possibilities, the dynamics of the evolution
of a galaxy, for example. Yeah, but it's cool to
play between those two. 'Cause it seems like
we understand so little about of our cosmos, so it's good to play. - Yes, it's like a big sandbox, right? And everyone kind of
has their little corner and they do things, but we we're all in the
same sandbox together at the end of the day. - And 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 get to
ask the right questions using that big, cool tool. Well, can we actually
step back on the big field of stellar archeology? What is this process? Can you just speak to it again? You've been speaking to it, but what is this process of
archeology 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. So 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. (chuckles) It comes straight from
a galaxy or, you know, 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 our Milky Way meant-
- They were eaten. - Exactly. 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, you know, these little old stars that are now in the
outskirts of the Milky Way that I use 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're still burning, for the experts, just burning hydrogen to
helium in their cores, and they have done so for the
past 12, 13 billion years, however old they are. And they're gonna keep doing that for another few billion years; same as the sun. The sun also just does
hydrogen to 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, you know, 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 today and going forward. So I'm a stellar archeologist because I don't dig in the dirt to find remnants of past
civilization and whatnot. I dig for the old stars in the sky because they have
preserved that information from these first billion years in their outer stellar atmosphere, which is what I'm
observing with telescopes. So 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? Are talking about something
that's close to that, you know, like a 13 billion, 12, 13 billion age range?
- Yeah. 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 and the
Milk Way for a second. So I already mentioned the pristine-ness of the universe
after the Big Bang, right, just 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, massive stars that they
would explode again, but also the little ones
that keep on living, right? And then the massive ones,
again, explode as supernova, so they provide, again, another sprinkle of heavier elements. And so over time, all the elements in the periodic
table have been built up. There have been other
processes, for example, neutron star mergers and
other exotic supernovae, that have provided
elements heavier than iron, all the way up to uranium, from very early on. We're still trying to
figure out those details. But I always say pretty
much all the elements were done from like day three. - So iron is where... Like, once you get to iron, you got all the fun you
need, most of the fun. - Yes and no. I really like the heavier
elements, you know, gold, silver, platinum, that kind of stuff. (both laugh) - For personal reasons
or for star formation? - [Anna] Well, both. (Lex and Anna laughing) - I mean, like, 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; we need that. And that's certainly what
came out of the first stars and then all the other supernova
explosions that, you know, 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, and that's why the sun has
the chemical composition that it has, including, you know, and somehow the planets where
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 just, it's a little bit more
of all of these elements. - Just more?
- Yeah. It's one sprinkle, then 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 seed
nuclei, ideally, you know, iron or carbon or something. So the supernova-made elements are very good seed nuclei
for other processes that then create heavy elements. And because they cannot be
made everywhere, when... You know, 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. - Well, wait. I thought I thought the really
old ones we would not have. So what does that mean if the old- - Ah, 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. Then we find other old stars that have a much more complicated
heavy element signature, and 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 informed, and that is what we're observing today. So all these old stars
basically carry the signature from all these progenitor events. And it's our job then to unravel, okay, which processes and which
events and how many, you know, may have occurred in the early universe that led to exactly that signature that we observe 13 billion years later? - Is it possible to figure out like the number of generations
that resulted in these stars? - Well, we can... 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 normal supernova explosion is actually already basically too much, it would give us too much of it. And the thing 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. - [Lex] Yeah, they'd take the whole thing, not just a little bit-
- They wouldn't take stuff out of the gas, you know? So we have maybe 10 stars or so now where we are saying they contained so little of these heavy elements that they must be second generation, because how else would you have made them? And, again, I wanna
stress that the elements that we observe in these stars were not made by the stars
themselves that we observe, that's just a reflection of the gas cloud. So we don't actually... I had to say that 'cause I love stars. At the end of the day, we don't really care for the
stars that we're observing, we care for the story
that they're telling us about the early universe. - Yeah, so the stars are
a kinda small mirror. into the early universe. - [Anna] Yeah, yeah. - And so what are you
detecting about those stars? Can you tell me about the
process of archeology here? Like, what kind of data
can we possibly get to tell the story about these
heavy elements on these stars? - Yeah, it depends really
on what star you find. There are many different
chemical signatures. We actually pair up, these days, our element 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 are in the galaxy, but they're not off the galaxy. That'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 came from. - Yeah. So we can't really say, "Oh, it came from that
and that dwarf galaxy." But interestingly enough... 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. And, again, finding
something that's really low means 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, 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... Well, now we come back to the protogalaxy. The protogalaxy was like a beehive. It just didn't really know what it was or what it wanted to
become when it grew up 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.
- It 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 looking-
- They're still doing it. - Yeah, A they're still doing it. And, B, we just looked for stars that have low strontium
and barium abundances and then we look at the
kinematics, and, lo and behold, they're all at hundreds
of kilometers per second going the wrong way. It's like, "Dude, you must
have come in 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're so fast
and it's really all of them, that must have happened early on, right? You can't throw a galaxy
into the Milky Way right now the wrong way, it eventually will turn around. - Can you actually,
just on 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 like, especially with undergrads? I think that would be very interesting and inspiring to people. - Yes, it was a wonderful
little collaboration that actually emerged in the fall. So I really like working with
undergrads and, you know, 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 cold email a professor, "Hey," you know, "I'm this and that person, and I'm interested in your research. Could I possibly, you know, come?" And I wanted to streamline that and give, and, you know, just trial how it would work to provide sort of the safe
confines of a classroom where you just sign up and do research in a very structured way. And 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 worksheets so that they could do it, again, in a very structured
and organized fashion. - Oh, so you created this whole framework for them to do it?
- Yeah, 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. Anyone can crunch numbers, anyone. It's complicated sometimes, but it's doable, right?
- Yes. - But coming up with a story when you only have three puzzle pieces, what does the puzzle look like? You have to be a little bit bold, you need to have some experience, and you need to kinda
see the universe in 3D. You just need to kinda 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 heavy elements. - [Ann] Yeah, exactly. - And you have to come up
with a story of all that. - Yes, 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 strontium stars
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 Milky Way, right? And it's so cool and it was so wonderful. So this class, it went
so well in the fall. I had nine people sign up. That's not unusual for a
specialty class at MIT, so a small number. It was eight women. And they were so into it that I said, "Okay, let's use this opportunity. You're gonna do some extra work with me and we're gonna 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? - [Lex] Yes, I search for
the most metal-poor stars. - And what does that... Can we just define what does that mean?
- 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-
- That's a good start. - 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." (Lex and Anna laugh) When I give public talks, I always ask, "Is there a chemist in the audience?. Let me just tell you, neon is a wonderful metal." And they're like, "Oh, my
god, what is she's saying?" But I'm an astronomer, 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 heavier than
hydrogen and helium, gets produced slowly but surely by different types of source and events. So that's, you know, 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. And that is the first stars, right? They started that process. That's why I said it was such
an important transition phase because things were... We call, you know, the post-Big Bang universe pristine, just hydrogen and helium, and after that the mess started. As soon as you add elements to it, things kinda get a little out of hand. That ends in this beautiful variety that we have everywhere these days. - Yeah, 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 organizable. (chuckles) But he variety of different types of metal-poor stars we have is stark. Many different types of stars, many patterns we have sort of identified, but there are still crazy ones out there that we're still trying to kind of fit in. - So what kind of stars
have been discovered? So you've already, a while ago, helped discover the star HE 1327-2326. Great name.
- Yes. - And HE 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? Is there cute names?
- Well, I'm probably the only one who can, you know, spit out these names without cheating. - [Lex] Are there nicknames?
- Well, no, that's their names.
- That's not allowed? Okay.
- Well, some colleagues at conferences have just called them
Anna star or Frebel star because they didn't wanna learn
the phone number, you know, I get it.
- The phone number. Yeah. - These numbers are actually based on older sets of
coordinates for these stars. So, yes, the minus in the middle means that they're in
the Southern Hemisphere. So negative is in the Southern Hemisphere, positive is in the Northern. And then 13 and 15 means
they're sort of observable in the middle of the year. - Okay, so it's the do
with the observation and where it was observed and that kinda stuff.
- Yes, yes. But they are very different stars. Both absolutely significant, career defining, actually, for me, but really pushed the envelope
in very different ways. So HE 1327, the first
one that you mentioned, that was the second
second-generation star that we found. And, you know, usually people say like, "Oh, the first one is a
big one and the rest is... Nobody cares." But 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 that's really great, but we need to show
that we can do it again. - [Lex] Mm-hmm, reliably. - Because then we're onto something and it's not just some
kind of weird quirk. And there are a lot of
quirks in the universe, but we wanna know: Is 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, we can find these stars. They provide an important
part to the story in the sense that if we
had more than two stars, and by now we have about 10-ish 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... 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 metallicity, so the overall metal content, the overall amount of
heavy elements in it. - So that's why it's called
an iron-deficient star? - That's right. So these stars are
incredibly iron deficient, which means there must be
of the second generation, because there was... And interestingly enough,
there was this discrepancy. A normal supernovae, until then, we thought would get us
so much iron, you know, and 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 III, we call them Population
III, the first stars, they must have exploded in a different way than we previously thought. They can't output as much iron because they just can't, (laughs) otherwise it wouldn't
match our observations. - [Lex] Got it. - And so that's when we started to work with several theory groups on supernova yields, so what comes out of- - From explosion of the supernova? - Yes.
- 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. (chuckles) And it's actually surprisingly difficult. Because you can always add
more in the universe, right, but you can't take stuff away. So our Japanese colleagues
kind of came up with the idea of a fainter supernova that
just doesn't have a much, has enough oomph, you
know, when it explodes, so somehow there's less iron coming out. But at the same time, then these stars showed huge
over abundances of carbon, you know, 1,000 times more carbon. So how do you now get
1,000 times more carbon out of these poor first supernovae, right? 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're not as
luminous and bright and energetic, that has consequences for
these early protogalaxies in which, you know, they must have been located
in terms of, you know, blowing the gas out, let's say, and disrupting the system. So much higher chance
for the earlier system to stay intact for longer, right? So there's a whole tail of consequences. And this is what I mean with: We need to find the story, because you do you one thing
and (mimics explosion), it's like the dominoes, there are consequences everywhere, and sudden you have a
different universe, right? - What could possibly
be a good explanation for something that yields a lot of carbon and 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, cooked up in order to
explain the observations... And 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, during
the supernova explosion, a massive black hole emerges. And so some of the material falls back onto the black hole. - Oh boy.
- So here is a vacuum cleaner now plopped into the middle, right? - [Lex] 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 star looks like, a massive star looks like in its interior before it explodes, you have hydrogen and helium
still on the outskirts and then layers of heavier
and heavier 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 wanna fuse to
iron atoms anymore, right, that's when the supernova
explodes, occurs really. It's actually an implosion first and then you have a bounce of
the sort of neutron star phase that occurs in the process
and then, you know, star gets disrupted.
- That is so awesome. - Yeah, it's like this giant, you know, basketball (mimics implosion) and then (mimics explosion) it all goes out.
- So implosion first, explosion after.
- 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 terms of the layers; you hold onto it, you don't let it escape. And carbon is much further
out, you let it all go. - Nice.
- And so- - [Lex'] So that explains
why you can have a big oomph and not much iron yield. - Yes. Yes. - So does explained the HE 1327- - Correct.
- and others like it? - Yes. So there's a... It'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 stars, right? So we had the hotter gas,
just hydrogen and helium, that made the first stars, there were hundred solar masses or so because the gas couldn't cool enough, so 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 stars. 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 stars. 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 a variety of reasons, because it just enabled
this whole evolution that we are now observing and literally seeing in the sky. And it's really 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. - [Lex] So carbon is kind
of important in many ways. - Yes, yes. - This is perhaps a interesting tangent. If I could just mention that you interviewed Mildred Dresselhaus of "Carbon Queen: The Remarkable Life of
the Nanoscience Pioneer." Is there something you could say about the magic of carbon
and the magic of Millie? (Anna laughs) - 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 nano work. So she was a material scientist, very far removed from what
I do on 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
the way that we can use it. It's wonderful. - Do you sometimes think
about this chemical evolution in this big philosophical way, that we're the results of
that chemical evolution, like we're made of this stuff, like we're made of carbon. - Yes. We're made of star stuff. Carl Sagan got it right. (laughs) - I mean , it's almost
like a cliche statement, but it's also a materials, a chemical, a physics statement, that we came from hydrogen and helium and somehow these formations created this interesting
complexity of soup that made us. What are we supposed to make of that? Like, what? Did we just get really lucky? Why do we get all this cool stuff? - [Anna] Yeah, that's a
good question. (laughs) - I don't think it's a
question that has an answer. I keep just asking why. But it is just this incredible mystery. So much cool stuff had to happen. So much, sorry, hot stuff had to happen to create us.
- Well, right. And so much could have gone wrong and there would've been
another outcome, you know? And it's actually amazing how many things kind of fell in place. I mean, maybe that's all
sort of self deterministic in some ways, right? We are who we are because
that was the path. (laughs) Maybe we would've ended up
being robots, I don't know. But it's certainly wonderful
to, you know, as scientists, for us to help contribute unraveling our cosmic history, right? I 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, certainly from a human perspective. - 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. (laughs) But, yes, everything
gets more complicated. - But there's also a beauty to the chemically pristine
universe in the early days. - Certainly is, yes. I love the desert with it's nothingness; it has 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. - [Anna] Yes. - That's another one of your babies. - [Anna] Yes. - 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 or 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 the sense that, yes, we have all the elements up to iron there. They 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, you know, different in quantifiable ways. But it has this huge overload
of very heavy elements. And what was so nice about
that star in 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 are thorium
and uranium interesting? They are radioactive elements, they decay. Thorium has a half life of
14 billion years, I believe., and uranium of 4.7, which, you know, to folks and us on Earth
is a really long time. But those kind of
timelines are really good when you wanna explore the
early universe. (laughs) So there are two questions
now that kind of come to mind. Where do these elements come from? And what do they tell us? Right? 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 there must be
lots of neutrons around. And,.again, when we talk about the site, we can surmise and ponder
where that might be the case. But you have this iron atom and you bombard it with neutrons, and you do it incredibly fast. Now, what happens in the process? That iron atom, you know, you collect lots of neutrons, it becomes really big and unstable. So it's a heavy neutron-rich nucleus that wants to decay (laughs) 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 timescale, so it will decay to a stable nucleus. So the neutron will convert to a proton, and that makes it stable. If you now bombard lots and
lots and lots of neutrons onto that seed nucleus within that timescale of the beta decay, that's how you get to this huge, fat neutron-rich nucleus that
then wants to decay, right? So the rapid process, as you have your seed
nuclei, they get bombarded, you create these really
heavy neutron-rich nuclei, they're 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 is what creates all the- - Correct. And the whole thing is done
within two seconds. (chuckles) So just to add to the rapid here, (fingers snap) in literally the snapping
of my hand, it's all there. In my talks, I often, I have this nice simulation
that illustrates, you know, this creation of these heavy nuclei. And I always say, "This is the only
simulation you will ever see that's slower than real time." Because in astronomy, you know, we show, "Oh, this is how a galaxy forms," 13 billion years in 30 seconds. Really short, right? This is the opposite. Me showing you this, the
elements are long made. - So where and when does this happen, does this process happen? - So you need the strong neutron flux. - [Lex] That's the
clumping of the neutrons at the nuclei?
- 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, you know, if the neutron star... 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, and so it's not too unusual to create a pair of neutron stars that will still orbit each other after both of their progenitor
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 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, but the process is completely different. And the cool thing is when
these two neutron stars collide, they produce a
gravitational wave signature because neutron stars
are super dense objects, they're like giant atomic nucleuses. 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 there's
this ripple sent out, you know, into the space time continuum,
basically, you know, the... What do people say? The ripples of space time, you know? It's like you drop a
rock into water, right, you see the waves coming. So that's exactly what happens when two neutron stars merge. And this is neutrons galore, right? It's really violent to smash
two neutron stars, you know, that are so dense already into each other. And 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. And then the neutron flux 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 astronomer saw,. in this
electromagnetic counterpart, the nuclear synthesis of
heavy elements occurring. And that's just awesome.
- That's amazing. - It's so awesome. - That's 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 the whole shebang, that happens in two seconds and creates a bunch of heavy elements. - So that confirmed that
one of the sites, for sure, for the r-process to occur
is neutron star mergers. Interestingly enough, I
have to mention this here, a year prior, in 2016, my former grad student Alex Ji and I, we discovered a small dwarf galaxy that is currently orbiting the Milky Way, it's called Reticulum II, that was full of ancient
iron-deficient stars that also had a strong signature of these heavy elements
exactly like HE 1523. 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. And I was dead set on showing 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 in the oldest stars, right? This is what we had seen anecdotally in the ancient dwarf galaxies
that are surrounding us. - So that's an ancient dwarf galaxy? That dwarf galaxy has a
bunch of ancient stars in it. - Yes. Yes. And so now we find Reticulum
II, 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. We have environmental information. They're not lost in the galaxy where we don't know where
they actually came from. No, we know these stars who
were formed in that galaxy because they're still in it." And we already deduced from that that it must have been
a neutron star merger that went off in Reticulum
II 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 II dwarf galaxy is that is orbiting the Milk Way galaxy? It's going to be eaten by it, presumably- - It totally is going
to be eaten. (laughs) I can't tell you exactly when. Yeah, the Milky Way remains surrounded by dozens of small dwarf galaxies. They're collections of stars. Some of them, we call them ultra-faint dwarf galaxies because they now only
contain, I don't know, a few thousand stars; very, very faint. - [Lex] But still detectable? - Yes, because they're fairly close. And we detect actual
individual stars in them. So I've observed some of the
faintest stars, you know, you can 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, right? They did not get eaten. So they're still in their
native surroundings. It's like getting the
lions in the wild, right? I gotta 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, it's not all of those
stars in that dwarf galaxy that are 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. It 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
stellar archeologists, 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 nothing has, literally nothing has happened to them. They've just been waiting there for us. - So from a stellar
archeology perspective, what is like juicier more interesting, the old stars in the outskirts
that have been eaten, on the outskirts of Milky Way, or the stars in the dwarf galaxies? Of all the things you love about the... You said you love stars, so which do you love
more of your children? - Hmm, oh, that's a hard one. I mean, I love them all, of corse. 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. (chuckles) - And they have interesting
kinematics, presumably. - Yes, and we can get that. And so HE 1523, for example, you know, that one is really bright. Only it's a red giant, 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 a dwarf galaxy star, so that's a big trade off. But the environmental information that we get along with
the basic information about these stars in each
dwarf galaxy is really, really valuable in establishing,
you know, for example, the site information, right? Because the galaxy is still there, so nothing crazy could have happened. So actually to close that loop, probably some heavy elements come out of supernovae here and there, but somehow my theory colleagues tell me that a normal supernova just
doesn't have enough oomph to really get an r-process
going and doing it all. - So you need these orbiting supernova. - We need probably the
neutrons 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 kinda get that
particular process going. But the normal supernovae
don't do it, right, so only a little bit comes out. But you could come along and say like, "Anna, why don't you just
take 100 supernovae together to build up the yield?" Right?
- Mm-hmm. - But then I come along and say like, "Look, this dwarf galaxy
is still intact today. If you would've plugged in 100 supernovae into this little system early on, it would've blown apart." It would have blown apart
past 5 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. - It'd be 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. - Well, yeah, astronomers
are doing it all night long, so we have lots of late nights. (laughs) - 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. There are 6.5-meter telescope, which means the mirror
diameter is 6.5 meter. That's not the largest
that there is out there, but it's among the largest. And I use a spectrograph
because I'm a spectroscopist. I don't take pictures. (laughs) 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, you know, let's say the eight-meter telescopes from the Europeans or so. So I'm very happy with that. - Efficiency meaning? - How many photons get
collected sort of per time unit because 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 they're sitting there
and collecting the data, making sure the data is collected well, the cleaning of the data,
the offloading of the data, all that kind of stuff? - Yeah, so it's mostly done for them. Obviously that's super
convenient, (chuckles) but it also takes away a central part of what 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 up
and see what happens." No, you know, we only have one experiment, which is the universe.. And what we see is what we get. (chuckles) And I think it's so important to take an active role in that. So I really love going to the observatory. I've taken many students
there over the years to teach them and to just show them what
it means to be an astronomer. Because you go to these
remote mountaintops, 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. (chuckles) - 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. It's very calm and the
colors are so beautiful. And I always become much
calmer when I'm there, A, because I'm just there
for one purpose only, that's 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
distractions because, you know, you're just there to do one thing. - And also the emails
somehow seem less significant when you're looking up at the stars. - It's just you can afford
to focus on this one thing, and 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. I have done a lot of
astrophotography there as well, so... And 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, there. And I would just lay there
like the snow angel, you know, (Anna laughs) 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 belong here, rather than feeling kind of small. Yes, I'm small, but there are many other small things. And lots of small things
make one big whole, right? - And we're part of that big whole. So that's looking at the inner spirals of the Milky Way galaxy. - 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 the starlight because
it's such a dark site and the stars are so bright. And these are kind of moments that kind of change you a little bit. And it's-
- 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, you know, we're one and the same. - Well, that fills me with hope that... 'Cause I tend to think of us humans as in the very early days
of whatever the heck we are. And so that makes me think
thousands, tens of thousands, hundreds of thousands of years from now, that we'll be reaching... Whatever we become will
be traveling out there to explore more and more and more. So 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. (laughs) - Coming up with different theories of what's on the other
side, that the Earth, starting to gain an intuition
that the Earth may be around and that we might be able to
navigate all the way around to get to the financial benefits of getting spices from India
or whatever the reason, whatever the grant funding
process is all about. But ultimately it actually results in a deep understanding of the
mystery that's all around us. And, I mean, just to travel out there... I mean, 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 kinda humbles you. And it's 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? We tend to have a very
human-centric perspective of what is a living organism and what is intelligence and
all these kinds of stuff. And all the work in
artificial intelligence now is starting to challenge our ideas of what makes human beings special. And I think we're doing that
through all kinds of ways, and I think you're working
some part doing that as well. Like, the unity you feel is realizing 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 what is... If you could just kinda linger
on the process of the data, what does the data look like? And how does the raw
data lead to a discovery of an ancient star? - Well, as a spectroscopist, we have to, I guess, talk for a brief moment
about what a spectrum is. Everyone, I hope, has
seen a rainbow in the sky. That is basically what we're doing. We don't send the starlight
through a raindrop that then gets bounced 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 gonna look
colorful, just black and white. Different colors have, of
course, different energies, that's what we record. More specifically, we
record as wavelengths. So wavelengths and frequency and energy, it's all the same at the end of the day. We 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, (laughs) it's a bit funny to
describe just with words, but a wriggly 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 and so we can no longer see
it as well or 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 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
are the observer, you know, 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, so you see less of them. And so those are the 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 spectra really look
like a straight line and then there's a dip here and then you have the straight line, again there's a dip there. The sun doesn't have
straight lines, I mean, it's just all absorbed
in some form or another. But the old stars have so
little of all the elements that only occasionally these
dips that then indicate, "Okay, that one at that
wavelength was iron. And here we have carbon, and
there's magnesium, and sodium. And, oh, there's a little
strontium line here." So we have a much easier
way to map out this barcode that the 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 sellar atmospheres, like how much was absorbed, how many, what kind of elements were present in the stellar atmosphere. And so this is how we get to
our abundance measurements and then altogether that gives
us the chemical composition and that particular
signature in that star. - Do you ever look at
like the raw spectrograph and the absorption line
and your able to see, intuit 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. We 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 kinda like reading
the tea leaves. (laughs) 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 look at further?
- Yes, exactly. And so it's thumbs up,
thumbs down. (laughs) 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, you know, we output that we have observed the star and their basic nature. That's an important
part to publish as well. And, yeah, I had a run... So now we do remote observing. I do all of this now from my
home, from my living room, all night long. (laughs) 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 gonna keep exposing." So we took 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 trying
to answer that question, as in like doing the search process. That'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? And I often don't find, but I keep searching because, you know, our 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 moves the field further. - And how difficult it is to believe that there is a thing to be discovered. - Yes, yes. We have this 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 are done, but you need to get there. (chuckles) - [Lex] Yeah. Probably the
first is the hardest, right? - Yes. But it kind of remains really hard. But the thing is then at past three, many of us are like, "Okay,
we've solved that problem. We've shown 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 on to the next thing. - That's an indicator that
there's many more of them, 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 a one
big bright light point. So it looks like a star, but it's actually just a
giant supermassive black hole that out shines its own galaxy. And people have been trying to study those and they had taken little
spectra of, you know, all things in the sky. And it turns out, oh, you can fish out the
actual stars from that and look for certain signatures that might indicate low-metallicity 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: Is it yay or a nay? (chuckles) These days, with another grad student, I developed a new technique to use images actually of
all the stars in the sky taken with very narrow filters. So it's like you're wearing
very specific glasses that only lets 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 space? - That's right. Because these stars are a little bit like the needle in the haystack, right? There are not that many left over. And certainly the galaxy has made plenty of stars in between; we need to comb through all
of those 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. No, I'm just kidding.
- We're all special, right? So are the stars. - It's good, it's inspiring, even if you're the outcast. 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, so this kind of collection
of data, looking, trying to kinda pull out the signal from the noise out there? - Well, that's literally what we are doing in multiple ways actually. So we're trying to find
a 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 be warranted given the potential of the star, right? It's like (groans). - So there's always noise, there's always a little bit of noise, and you have to try to say like, yeah, "How special is this," when you're looking at
the absorption line? How-
- Yeah. So the most iron-poor stars, 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 a strong function
of the brightness of the star because the telescopes have
the size that they do that, that's not gonna change for a while; hopefully eventually it will, but it's gonna 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-poor star
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." (Anna laughs) 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 like the most exciting
discovery to you personally? Is there a moment you remember
that you saw a piece of data and you kind of, your heart skipped a bit? - Yeah, yeah, of course. - Is it HE 1327? - That was definitely
one of those moments. I wasn't actually
present at the telescope, but we were sent the data
immediately from our colleague. And we just looked at it and our eyes got really wide and was like, "Oh, my god. (laughs) Is this really what we 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's 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 now? 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 white dwarf... A white dwarf is the leftover core of a star like the sun
that has gone extinct. And white dwarfs have lost
all their a outer atmosphere, so it's just a hydrogen and helium core. So they look like a metal-poor style because there's only
hydrogen helium left, right? But the hydrogen lines that
you can see in the spectrum of our stars and of the white 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 it does? Is this a white dwarf
who's fooling me here?" Right? And so it's like this moment,
it's like, "Oh, my god." - [Lex] It's just minutes of nervousness. - Yes. Yes. And sometimes, you know, it's a dud and sometimes it's not. - What's been a big, that
you remember, heartbreak, like a painful low point? Is it all leading up to
the first... (laughs) Is it all about HE 1327 again, just the leading up to it? Or has there been like a... Yeah, has there been like
low points in the search? - That's a good question. I mean, you know, it starts with mundane things as in like you won your telescope time, you traveled there, and the weather is
completely cloudy, it rains, and you had three nights, which is a lot, and you go home empty-handed. So that's definitely a low point. (laughs) Probably not what you were thinking of, but there is a certain
occupational hazard to it. - Which requires a kinda
resilience and a patience. - Yeah. And you just gotta
learn to live with it. Coming back to Reticulum
II, 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 2:00
AM and he was like, "Anna, I think I observed the wrong star. I'm so sorry. There is this line there,
this europium line, and 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, and 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? And he calls me back an hour later, "Anna, 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. It was an r-process galaxy, the first one we had ever discovered. Totally, I mean, unpredicted. 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? Neutron star mergers happen 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 r-process stars are in this galaxy. So we managed, by a hairline, to observe the nine brightest stars, but the data quality was atrocious. - [Lex] And the weather
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 it's a nay?" 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. - [Lex] 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? - [Lex] That was super high stakes. - But we just made it, like, 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 it stuck out of the noise. If the 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 like, "Yes, this is it." So that was quite the night. (laughs) - Luck. I mean, a lot
of this is just luck. So that was the first
r-process galaxy discovered? - Yes. I didn't sleep all that
much that night. (laughs) - Do you have hope... Are you excited about
James Webb Space Telescope and other telescopes in the future that increase the resolution and the precision of what
can be detected out there? - Absolutely. JWST 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 are just kind of looking at different sides of the fence, right? 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, you know, energy and elements and all these things. And my JWST colleagues, they try to detect some
of these earliest photons from these earliest systems to look at the energetics
and other things, you know, 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. - What do you think is the future of the field of stellar archeology? 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 or is it two or it three? Right? Is it a sample? Is it a population? So we haven't concluded
that kind of work yet. - So every metal-poor star
is a kind of data point that you can use to improve
the quality of your model of the evolution of the early universe. - Yes, yes. And I would say 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 dying down a little bit because of all the progress. It's on the up 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. I'm sort of this of older generation. I have only very few colleagues,
I work 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 certainly not in the end stage. And, you know, I'm not a
big data kind of person, although we're all headed that way. I certainly use data from the
Gaia astrometric satellite for the kinematics, for example. But that's personally a new thing for me 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. I have enjoyed that a lot, but that's about to change. - So one star at a time.
- Yes. - I mean, there's power to that, to build up intuition of
the absolutely universe by looking one star at a 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, otherwise you have the
data that you have, right, you get what you get
and you don't get upset. (Anna laughs) 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. - Sometimes a lot is lost in the aggregation of the noisy data. - Yeah, yeah, yeah. And there always the danger, if you have someone else's data, that you just don't really
understand, 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's 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 question really well because otherwise you're
gonna get an answer to a different question but you won't notice that the goalpost 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 leads 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, and 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. (Lex and Anna laughing) That works for me. - So I don't know if it's possible to say, but where 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? Where are the discoveries in this field that you think will come? - I think the individual
discoveries are actually... We've made most of those, certainly through individual stars. Finding yet another second-generation star is 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. And new search techniques and new surveys may enable that. But would you still call that a discovery? Right? - [Lex] So that's just a scale, that's 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 are a person like me, I wanna get to the last ones. I'm not gonna leave it just like, "Okay, I see broadly what this
is gonna look like," right? "I'm done now." No, I wanna get to the last one. So is the picture
globally going to change? No. Are we gonna figure out all the details and how it really works? Yes, right? - So really careful, detailed map out-
- Getting into it. - the ancient stars of our universe. - Yeah, because I think that's what... Many of the 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 10-sigma
discoveries become less and less. If they were easy, we would've
made them already, right? Which means we have made many of them. But 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 10 new open doors that we wanna explore and march through. And that's the, you know, finding these last puzzle
pieces here and there that really make it airtight. - And so there's a lot of value and a lot of power and
beauty to the discovery in the big picture of our
universe and in the details. So both are really important.
- Yes, we need both. Absolutely. - Perhaps drifting into the philosophical, let me ask about the Big Bang as we kinda 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, you know, stars only probe the time
when they were formed, and the Big Bang is surely before then. I mean, I often talk to my students about the difference
between math and physics. Let me give you an example. We talked earlier about
HE 1523, and, you know, I was happy to share with you that I measured thorium and 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, right? 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. This 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 averaged 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 some 10, right? Is 15 correct." And then I ask them and some
people will say something. And 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? - [Lex] Correct from a
mathematics perspective. - Yes, 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 a separate issue. - So you're saying physicists
are much closer to truth than mathematicians? - Well, it depends.
- I'm just kidding. - Sometimes yes and sometimes no, right? So what our job as physicists is, 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 a special case because
we don't actually know what's supposed to make sense. (laughs) And this is where things get interesting, but 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
at the singularity of things. - Well-
- Or no. - depending on who you ask. - [Lex] Okay. Sure, sure. - This is the current question, right? 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 and the back? What's the front? The front is the-
- Well, before the Big Bang. - Oh, before the Big Bang? The front, okay. (Anna laughs) Just to clarify all the
doorways and the entrances. - So how far can we let the math go before that stops to make sense, right? And I don't know what
the answer is to that, but it's really cool
because math doesn't have, is 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 judgment free because it just calculates
things on its own, whereas, as physicists,
we are so judgmental: "This makes sense. This doesn't make sense," right? It doesn't get any worse. - It's such a beautiful dance. It's so amazing that through this dance you can explore the
origins of the universe. Like, doesn't the Big
Bang just blow your mind, that this thing just started from a point and now we're here? - [Anna] Yeah, yeah, yeah. - Hydrogen and helium and then all the stuff you're studying. I mean, this evolution of chemistry created humans and we're here talking. And here's a lot more to the story. It's amazing. - [Lex] Yeah, yeah, yeah. - And this kind of march that you're doing is observing data. And is there... You're looking at old light and old data. - But only a few thousand years, right? - [Lex] Just a few thousand years. - That's the difference between
me and my JWST colleagues. Their 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 nothing. - So whatever you observe now is likely still going on. - Yes. These stars are alive and
kicking and having a blast. - A thousand years, just a few thousand years is all it takes. If we can travel close
to the speed of light maybe we can reach out there. - We wouldn't have any planets
around those stars, though. - Is that a definitive intuition? - Well, what a planets made of? Elements, right? Take the Earth, it has all heavy elements, right? The 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're... 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? - [Anna] Yes. - Not that they're... They could be good
vacation spots, but not... Well, if you like it warm. (laughs) Just no planet islands to go to to chill. - In your book, you highlight the major contributions in the field by many women. Some of these women were
not, as you describe, immediately credited
for their discoveries. So for me, from a computer
science perspective, the story you also tell
is Harvard Computers. Who were these women? And what can you just say about the nature of science and humanity? - Discovering things is part
of the human nature, right? And so it's happened for the longest time, not just by men but also
by many women. (laughs) The field of stellar
astronomy, which is my field, has particularly benefited from many discoveries made by women. You mentioned the Harvard Computers, that's a term used for women who worked about 100 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 service 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, well, one or two dozen women over the years, were hired 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. So they weren't robots as, you know, the term computer would perhaps lead on. So Annie 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 that
classification sequence today. Cecilia Payne-Gaposchkin,
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. - That's a gutsy, amazing discovery. - Yes. It was later termed the most
important thesis of humankind or something like that. (laughs) 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 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, now it's called nuclear astrophysics. And so many women had many
contributions to that. Of course prior to that Marie Curie discovered two new elements. Ah, so awesome. (laughs) Radium and polonium. Lise Meitner discovered nuclear fission, 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 bombard it with a neutron, we talked at length about
it, it will decay... Well, not decay, actually. It will fission, 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 fission cycling that she calculated in 1938, 1939. So, many, many contributions. And it's just so remarkable. I 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, all of it just taken together, ultimate progress.
- That's progress, right? Science is what it is, we have to decide what we do
with that knowledge, right? We can always use things
for good or for bad. 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 make this whole
ride so damn interesting, about what'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 still. - Yes, yes. Lise Meitner 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, so case in point. - Yeah. And, of course, the Nobel
Prize has its complexities. One is the credit assignment; but two, even in astronomy, sort of assigning credit
to a handful of folks when so many more contributed
is a complicated story also. - [Anna] Yeah, it's very complex. - Okay, sorry for the romantic question, but what to you is the most
beautiful idea in astronomy, in stellar astronomy? - Well, so early on, you know, when I was in high school, I was thinking like, "Okay, what do I wanna do when I grow up?" Right? (chuckles) I knew 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 Curie was a big role model. My friend actually made a beautiful, produced a beautiful movie about the discovery of the elements. It's a theater play, but digitized. When I saw it, I could actually kind of relive the sort of discovery
moment that Marie Curie had. It sent shivers down my spine. It was fantastic. I mean, this is the kind of thing that I wanted to experience. But, yeah, so nuclear physics and element creation and formation was really
interesting to me, chemistry, the elements,
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 met 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 it's 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. We can get these clean
signatures that help us inform the nuclear synthesis processes, you know? And, of course, I need to
know a lot about stars too. So it's like all together. And that was sort of a moment of magic. And then the fact that I have
now done that for 20 years is 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 am fortunate enough to
be able to keep doing that. And I'm happy to see
where it will take me. You know, it's an evolution. As with every relationship, if you don't march forward,
you move backwards. I'm not interested in moving backwards, so I'm letting the field
and the discoveries and the findings lead me to... You know, and I'm often... It's not hard for me to
follow sort of my hunches. And sometimes even at
the telescope, it's like, "Hmm, let's take a look at this one. I have a good feeling." And then usually something
good or, you know, not bad pop pops out at the end. And 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's really important to me, and I certainly try to make use of that. I also try to teach that to others, to trust them, to learn... You need to learn your things, but then you need to
also trust that knowledge and that 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, our cosmic history, that's a wonderful thing. (laughs) - And in this way, your personal love story
with the stars evolves. 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? - It seems increasingly
hard for folks to find that. Sometimes I feel that, you know, young people have all the
opportunities these days, and that's wonderful. But it's almost like that leads to some... What's the right word? They're a little bit 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. I'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 really dig in at least for some time and
get the hands real dirty and really learn from the bottom up. - [Lex] One thing. - On one thing, because they're afraid they're missing out 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 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 I have other
interests too, but I realized, "Okay, I can only do one thing." So I have no regrets. But this is a general feeling that I would think most of us have. But if it stops you from really digging, drilling down on one thing, to become an expert in one thing, to become really good at one
thing that you call your own, then it just makes it difficult. - And so a fulfilling life is in part likely to be discovered in a singular pursuit of a thing, of one thing. - [Anna] Well, yeah or- - At least for a time. - Yeah, for some time, with your heart and your hands. Because I think most people
long to own something. You know, we all, I think, wanna leave some legacy of some sorts, you know, for our children, for humanity, for this planet. (laughs) And 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 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- - [Lex] Just narrow down,
narrow down, narrow down. - let out what's not on your plate, and then this way we
get a little bit closer. And then it's like, "Well,
why don't you take a risk and just sign up for
something for three months? You can afford that."
- But that's what it feels like. That's what it feels like;
and it is that, it's a risk. Commitment is a risk.
- Yes. - Because it's you're
basically sacrificing all the other possible options. But then I guess you have to trust the magic you noticed in that thing. If you notice one thing,
just stick with it. And then maybe there's something there. - Right, right. 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 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 to find out. - And then there is that. Yes. - Somehow, it doesn't make sense. You also mentioned that you
have taken a little stroll into the artistic
representation of yourself. Can you speak to that for a little bit? - Yes. Well, I already just mentioned
sometimes I wish I, you know, had more time to do other things. So I find little sideways, I guess, 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 Lise Meitner who was an Austrian
German nuclear physicist. I'm from Germany, so I have
the right accent for that. (Anna laughs) And we wrote this play about this moment of
discovery of nuclear fission. 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, 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 re-live, for people,
the moment of discovery, then I turn into myself and then I give a 30-minute presentation on the r-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. And it's a wonderful compliment that almost spans 100 years
from one woman to the next passing on the torch. And, you know, when we write up our
results, let's say, you know, in magazines like "Nature and Science," it's always about the results
on the golden platter, perfectly prepared. The discovery is never described, only ever the results. You asked 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 ever, nobody really talks about it. And so having a form of, you know, theater of the arts to
bring this exciting moment, 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. I was looking for something
and then I found it. It's like you misplaced
car keys, right? (laughs) - Or love.
- Yes, yes. Everyone can understand that.
- Both are glorious experiences, yes. - The implications and the findings, that is much harder to
understand 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, "Ah, here is
the moment of discovery. Let me tell you about it. It profoundly transformed me. And here's how it went," right? It'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 it's people doing it. Maybe not a problem, but that is it.
- That's also what makes it beautiful, right? I mean, humans are fascinating in that we're able to
come up with these ideas through all the struggle, through all the hardship,
through all the hope, through all the search we find- - 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? "I need to find these car keys. I need it because I need to go," right? It's like, "Now, now!" (chuckles) And then, "Oh, God, here it is. Now I can go my merry ways." 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. - [Lex] I hope so too. I would love to see it
- So far I'm just doing it in person, (laughs) but it's really nice. - I would love it. I think a lot of people
would love to see it, so 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. What's the meaning of this whole thing? 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 played 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 laws of physics sort
of work the way they do. And we talked much about the
variety of everything, really, 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 was a
necessary consequence of that. In 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. That's not truly
satisfying to a scientist. - So 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, whatever, whatever disciplines. It's turtles on top of turtles. - Turtles all the way
down, yes. (chuckles) - And you have studied some
of the most ancient turtles at the very bottom of the thing. (Anna and Lex laughing) - That's right. That's right. They live for quite a while. - Yeah, 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 your work. And thank you for everything you do. And thank you for talking today. This was awesome. - Of course. It was wonderful. Thank you. - Thanks for listening
to this conversation with Anna Frebel. To support this podcast, please check out our
sponsors in the description. And now let me leave you with
some words from Douglas Adams in "Hitchhiker's Guide to the Galaxy": "Far out in the uncharted backwaters of the unfashionable end
of the western spiral 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-green planet whose ape-descendant life forms
are so amazingly primitive that they still think digital watches are a pretty neat idea." Thank you for listening. I hope to see you next time.