Kind: captions
Language: en
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 a
part of it I 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 hole
the following is a conversation with
Anna for about 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 Friedman podcast to
support it please check out our sponsors
in the description and now dear friends
here's Anna for Belle
let's go back to the early days what did
the formation of the Milky Way galaxy
look like or maybe we want to 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
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 and
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's fairly hot gas
and so the very first stars that formed
prior to 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 that course All
Stars fuse lighter elements like
hydrogen 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's at the stage for everything
else to happen including us here talking
today so what do you mean by pristine so
there's a whole
uh 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
um and after these very first stars
formed and exploded they and the heavier
elements like carbon oxygen magnesium
iron all of that stuff was was suddenly
present in the gas clouds
tiny amounts only very tiny amounts but
and that actually helped especially the
carbon and the oxygen to 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 that gets colder and colder you can
make smaller and smaller Stars so you
can fragment it and Clump it and turn it
into stars like 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 masters 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 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 older stars and
it's like unpacking everything that 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's giant Stars that's mostly
hydrogen helium then they exploded in
these Supernova explosions and then they
made these clumps
yeah so the first one is pristine
non-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
it's just changed it completely right
and that changed the physics of the gas
so that meant that these these gas
clouds that were you know surrounding
the the Forma 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 to still
observe some of the stats that form back
then so we are testing the the
conditions of 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 well legitly yeah
when I was in high school the universe
was 20 billion years old yeah so the
estimate did you change do you think
that estimate will evolve in interesting
ways or no is that is it I think it's
mostly converged yes because the
techniques are very different now much
more precise the whole business of
precision cosmology by mapping out the
cosmic microf background you know that
that's a marvelous feat
um maybe you know the digits will still
move around a little bit but that's all
right plus the gravitational waves and
all that all the different sources of
data yeah 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 half a 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 half a billion years and
um that was the time when sort of the
very first pro photo galaxies formed
early Stella structures Stella systems
from which the Milky Way eventually
formed right so it was the Mickey was
probably a bigger slightly bigger one
and we know today that galaxies grow
hierarchically which means they eat
their smaller neighbors so if you're the
bigger one and have a few a few friends
around you're just gonna
um eat them absorb them and then you
grow bigger and
um so all these these little early Stars
you know kind of came into the Mickey
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 deaf and just left
there since so the old stuff is on the
outskirts of the Galaxy and the new
stuff is in closer to the middle is
there broadly speaking okay yes because
that's where you would look for it so
maybe it's just a step back like what is
a Galaxy what is the part of the Galaxy
I love that question so the Galaxy is
um
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
disk and when we look at the night sky
what we see as The Milky Way band on the
sky that is actually the it more the
inner the next inner spiral arm because
we actually live in a spiral this
galaxies are the Mickey who has a spiral
disc Galaxy
um and we're looking
um actually depends a little bit in the
northern hemisphere we're looking out of
the Galaxy so we're 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 South uh to the southern hemisphere
let's say South America you see the make
you and it looks so different on the sky
because that's the next inner spiral arm
and that's backlit by the galactic
center
the galactic center is is a very big
puffy
you know region of gas there's a lot of
star formation that the galactic party
is happening there so it's very bright
and it it makes for this very beautiful
Milky Way on the night sky that we see
so actually if you 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're
sitting in this kind of disc in this
pancake and you're just kind of looking
right into it and you can you can really
feel that we're in this 2D disc
and then you can imagine that there's a
top and the bottom and that that we
really part of the Galaxy you can really
experience that we're just not 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
Mickey wear 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 I don't know I 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
um I think for many people they think
like oh that'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 there's so much more and I
really like to imagine wow I'm 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
um 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 pictures of a nice vacation
place
all we get is that light and old light
is 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 to space and see the
Earth and other things from from up
there there's there's certainly that but
I don't know it's it's also okay it
would just be at our vantage point and
and see it from from here with the
sensors with the telescopes that we have
and explore the possibilities yeah I
mean there is a kind of wander to the
mystery of it all what 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
um
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
um
I used to think what kind of Worlds
there are because they're probably
really creative living organisms
because 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 I already mentioned the number of
stars in the galaxy I mean you know
that's it's a huge number of planets out
there so who knows what that looks like
all we know is that there's
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 right maybe the Dynamics
of Planet formation like exoplanet
formation or Star formation the whole
all of it all of it
our formation is remains a much research
topic
it 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
um it's very hard to 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 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 yes so you we just don't know how
this turned out in an individual case
and it's kind of hard to
to figure it all out and and to take a
look certainly with planets right the
chance forever to ever actually take a
picture of a planet is minuscule because
they don't shine so they're really dark
yeah so I'd say there's there's a lot of
possibility out there
but we have to be a little bit more
patient before we come up with
Technologies where patience becomes less
necessary by extending our lifetimes or
or increasing the speed of space travel
all the kind of stuff he was a pretty
pretty intelligent they're pretty uh
sometimes yeah for the most part I hope
and now when I'm on the optimistic days
well maybe just to linger on the on the
what a galaxy is
um what should we know about our
understanding of black holes in the
formation is that an important thing to
understand in the formation of a galaxy
like uh so all the orbiting all the
Sparling 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 want to come back to the
the idea of the Proto Galaxy because
it's actually matches or you know
relates to to the black hole formation
so most large gal well pretty much all
large Galaxies have a supermassive black
hole in the center and we don't actually
know don't we don't really know where
they come from again we know that they
are there but how how do we get there so
if we go back to the to the early
Universe right we had a a little Galaxy
that just sort of you know I don't know
had some small number of stars it was a
first gravitationally bound structure
that 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 it
started to hold
um gas and then Stars sort of together
in this first very shallow
um what we call potential well so these
gravitationally bound systems
and then the Milky Way 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
I'm not actually sure that it's clear
right now kind of what was there first
the Supermassive Black Hole uh 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
um but it's that's a it's a big area of
research and the new um James Webb the
jwc the telescope the infrared telescope
in space is um is working on many people
are working on that
to to figure out exactly what what
happened and there are some some
surprising results
um that we really don't understand right
now so so to solve the uh the chicken or
the egg problem of uh do you need a
supermassive black hole to form a Galaxy
or does the Galaxy naturally create the
supermassive black girl yeah yeah I mean
I
we can't answer that because there are
lots of little dwarf galaxies out there
you know the Milky Way remains
surrounded by many
dozens of 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 they are certainly were
gravitationally bound structures so
either you can call them proto-galaxies
or dwarf galaxies or first galaxies they
were definitely there
but there must have been bigger things
like the Proto Mickey way where
something was different right what made
them more massive so that you know they
would gravitationally attract these
smaller systems to to integrate them
so we'll have to see how do we look into
that the into the the Dynamics of the
formation the evolution of the portal
galaxies is it possible that they shine
I mean what what are the
set of data that we can possibly look at
so we've got gravitational ways
which is really insane that we could
even detect this
um there's the light
what else can we uh so that that would
fall into the category of observational
cosmology and the the jwst is is the
prime telescope right now to any
promises big big steps forward this is
in its early days because it's only been
online like a year or so
um but that collects the infrared light
from the farthest
like literally Proto Galaxy's earliest
galaxies that light has traveled some 13
billion years to us and they are
observing these faint little blobs
um and folks are trying to you know
again study the early the onset of these
early supermassive black holes how they
shape Galaxy so they're they're seeing
that they are they were there you know
surrounded by already bigger galaxies
ideally I'd like for for my colleagues
to push a little bit further hopefully
that will eventually happen in terms of
looking towards the older and older ones
yeah yeah 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 that way 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
um
yes in a sense because it it all started
really small
or smaller yeah
in that phase of the universe it would
otherwise it it doesn't yeah uh just to
take a small attention about black holes
and
you know because you do quite a bit of
observational cosmology and maybe
experimental
um astrophysics
um
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 above black holes
destroying information
do those worlds intermixed to you when
you especially when you step away from
your work and kind of think about the
mystery of it all
um well at first
adversely much crosstalk
personally I mostly observe Stars so I
don't usually actually think too much of
black holes about black holes and stars
is a fundamental kind of chemical
physical phenomena that doesn't that's
right the physics is kind of different
it's not extreme yeah um 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
yeah but it's it's just a different
flavor and I don't I don't do these
kinds of calculations myself either
um
I 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 it's just I've written a
number of um papers with colleagues who
do like simulations about galaxies and
so they're they're not quite as far
removed as let's say the the black hole
you know pen and paper folks but um even
in those cases we had the same interests
in the same topics but it was almost
like we're speaking two different
languages and we weren't even that far
removed you know both astronomers and
all
um and it was really interesting just to
take that time and really try to
to talk to each other
and it's it's amazing how
how hard that is
you know even amongst scientists we
already have trouble talking to each
other imagine how hard it is to talk to
non-scientists and other people to try
you know to
we're 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 really takes a while to to
converge and to 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 our
differences not 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 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 try 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 a different
set of backgrounds and the researchers
that do that kind of work and probably
the same is true in um
observational cosmology and simulation
so it's a it's a it's like a
fundamentally different approach to
understanding the universe
let me use 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 create a bunch of
universes and see in a way that matches
experimental data as a as a fun it's
like playing Sims but at the cosmic
level yeah so but and then probably the
set of terminology used there is very
different and uh maybe you're allowed to
break the rules a little bit more let's
have you know yeah take the Drake
equation yeah you don't really know you
kind of come up with a bunch of values
here and there and and just see how it
evolves and from that kind of into it
the different possibilities the Dynamics
of the evolution of a galaxy for example
yeah but it's cool to play between those
two because we it seems like we
understand so little about our Cosmos so
it's good to play yes it's like a big
sandbox right and everyone kind of has
that little corner and they do things
but we're all in the same sandbox
together at the end of the day but in
that sandbox does have super powerful
and super expensive telescopes that
everybody's also all the children are
fighting for the resources to to make
sure they guess get to ask the right
questions using that uh big cool tool
well can we actually step back on the
the The Big Field of Stellar archeology
uh what is this process can you just
speak to it again you've been speaking
to it but what what is this process of
archeology in the cosmos yeah it's uh
it's it's really fascinating so
um I mentioned the the lesser the mass
of the star the longer it lives yes
yes and again for reference
um for the next dinner party the son'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 that's an important range for
our conversation because even 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 is nothing
so to me that's Young
oh it comes straight from from our
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 a
Milky Way Bend exactly they're formed in
a little other galaxy in the vicinity
and at some point the Milky Way ate that
which means it absorbed all the stars
including you know these little old
stars that are now on the outskirts of
the Milky Way That I Used to point my
telescope to
so
what can we learn from these Stars why
should we study them now these little
stars are really really efficient
um with their energy consumption they
are 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 all they are
and they're going to keep doing that for
another few billion years same as the
sun the same Sun also just does hydrogen
helium burning and we'll 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 in its outer layers
is exactly the same as the gas
composition from which the star formed
which means it has perfectly preserved
that information from way back then all
the way to the day and going forward
so I'm a Stella archaeologist because I
don't dig in the dirt to find remnants
of past civilizations and and whatnot
I dig for the staff or the old stars in
the sky because they have preserved that
information from this first billion year
uh years
um in their 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 or
talking about
something that's close to that you know
like a 13 billion 12 13 billion age
range that's what we what we think now
it has a small caveat here we can not
accurately date these tasks but we use a
trick to say oh these tests 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 Milky Way for a second
so already mentioned the
uh the pristineness of 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 than 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 so and then
the massive ones again exploded
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 Fair
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 I know
uh I I really like the heavier elements
you know gold silver Platinum that kind
of stuff
for person reasons they're for Star
formation well both okay
I mean like what's the importance of
these heavier Metals in uh in the
evolution of the Stars
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
um 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 a thousand
generations of supernova explosions
and that's why the sun has its its
chemical the chemical composition that
it has including you know and somehow
the planets were 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 yeah and then it's just it's a
little bit more of of all of these
elements just more yeah just 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 are 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 a very good seed nuclear for other
processes that then create heavy
elements and because they cannot be made
everywhere they when you when you know
so I my sum 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 if the old yes
important clarification
um so
the stars that we are observing today
these old ones they formed from the gas
and the question is what enriched that
gas ah so it could have been just a
first star dumping their elements into
that gas all the way up to iron
and we have found some stars that we
think are second generation Stars so
they form from gas enriched by just one
first star that's super cool yeah
then we find other old stars that have a
much more complicated
um heavy element signature and that
means okay they are probably formed in a
gas cloud
that had a few things going on
such as maybe a first star maybe another
more normal Supernova and maybe
some kind of special process like a
neutron star merger that would make
heavy elements
and so they created a local chemical
signature from which the Next Generation
star then formed
and that is what we're observing today
so all these old Stars basically carry
the signature from all their this these
progenitor events
and it's 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 observed
13 billion years later is it possible to
figure out like the number of
generations that resulted in this
um in these Stars well we can we we
think we can sort of say okay this was
like second generation or third because
the amounts of heavy elements in in the
cells that we observe
um is so tiny one Super One normal
Supernova explosion is actually already
basically too much it would give us too
much of it and the thing is you can
never take away things in the universe
you can only add there's no Cosmic
vacuum cleaner going around sucking
things away
the black holes are probably the closest
to that but they would have taken the
whole stop yeah they'd take the whole
thing not just they wouldn't take up
stuff out of the gas you know
um so we have a
maybe 10 stars or so now where we where
we are saying they're contained so
little of these heavy elements that
there must be second generation because
how else would you have made them and
again I wanna I wanna stress that the
elements that we observe in these stars
were not made by the Stars themselves
that we observe they that's just a
reflection of the gas cloud so we don't
actually I had to say that because I
love Stars we don't at the end of the
day we don't really care for the stars
that we're observing we care for the
story that they're telling us about the
early universe so yeah so the stars are
kind of a small mirror yeah into the the
the earlier yes yeah
and so what are you detecting about
those thoughts can you tell me about the
process of archeology here like what
kind of data can we possibly get to tell
the story about
um these heavy elements on the Stars
that depends really on
um what store you find
um there are many different chemical
signatures
um we actually pair up these days our
our
um our element signatures with also
kinematic information how the star moves
about the Galaxy that actually gives us
Clues
um as to where the star might have come
from because again all these old stars
in the galaxy but they are not off the
Galaxy 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 so I'm just I 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 it must have for it 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 that's incredibly low
in terms of the abundance it
maybe just one event contributed that
Max
so
we looked at the kinematics how are
these Stars moving and they're all going
the wrong way in the galaxy
how how is that possible well it is
possible because consider now we come
back to the Proto Galaxy the Proto
Galaxy was like a beehive it just didn't
really know what it was or what it
wanted to become when I grew up
so 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 still doing
it yeah the a they're still doing it and
B we just looked for stars that have low
straw human barium abundances and then
we look at the kinematics and lo and
behold they are 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 in to the Galaxy and
because they are so fast
um and it's really all of them that that
must have happened early on right you
can't throw a Galaxy into the Mickey
right now the wrong way it eventually
will turn around can you actually just a
small tangent speak to the the three
women undergrads like this little it's
pretty cool that you were able to
um
use a hunch to find this really cool
little star
um yeah what's the process of 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
um I
so I like I really like working with
with undergrads and grad students
postdocs
um 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
um people find it really hard to called
email a professor hey you know this is
I'm this and that person and I'm
interested in your research could I
possibly you know come yes and um I
wanted to to streamline that and give uh
and you know just trial how it would
work to provide a sort of a safe
confines of a classroom where you just
sign up and do research in a very
structured way
and uh 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 created
this whole framework for it for them to
do the whole thing
um 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
scientist is
to find the story anyone can crunch
numbers
anyone
it's it defines 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
that you have to be a little bit bold
you need to have some experience
and you need to you need to kind of see
the universe in 3D you just need to kind
of go for it and that's the beautiful
thing I really love that and so this was
a story of weird kinematics going the
wrong way combined with this particular
weird signature in terms of the elements
exactly and you have to come up with a
story yeah and so the story of that
paper is now usually I don't say I find
the older stars you know when I talk to
my research colleagues I I talk to them
about we find the chemically most
pristine stars because that's actually
what we measure the chemical abundance
that tells us okay it must have been
second or third or fifth generation of
stars right but these low strong theme
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 Mickey way right and this is so
cool and it was so wonderful so this
class it it went so well in the fall I
had nine people sign up that's not
unusual for for classic specialty class
at MIT so small number it was eight
women and they were so into it that I
said okay
let's use this opportunity you're gonna
do some extra work with me
and we're going to publish this try to
publish yes I also like that
um 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 the description of age so
there's this term of metal poor Stars so
most of these old stars are going to be
metal poor yes I I search for the most
metal poor stars and what does that can
we just Define yeah
I don't know who came up with this I
would I would love to know but um
the universe is a complicated place so
many decades ago someone clever came up
with the idea to say
let's simplify things a little bit let's
call hydrogen X helium Y and all the
other elements combine Metals Z
[Laughter]
when I give public talks I always ask us
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's
he saying but I'm an astronomer I'm I'm
not a chemistor I'll get away with it so
if you just roll with it for a moment
all the elements except hydrogen helium
are called metals
now if we look again at chemical or the
concept of chemical Evolution it means
more and more of all the elements
everything heavier than hydrogen helium
gets produced slowly but surely by
different types of stores and events
so that's a you know a monotonously
increasing function
um 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
they started that that process that's
why I said it was such an important
transition phase because it things were
we we call you know the the post big
bang universe pristine just hydrant
helium and after that the mess started
if you soon as you add elements to it
things kind of get a little out of hand
that that's that ends in this beautiful
variety that 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
um but the the variety of different
types of metal poor stores we have a
stark
um many different types of stars many
patterns we have sort of identified but
they are so 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 uh already a while
ago uh helped discover the star he
1 3 27 23 26 great name yes and I Chief
15230901 what can you say about these
these stars and others that have been
found I love them okay they're my baby
Stars what do you call what do you call
what do you call your your baby Stars
well I'm probably the only one who can
you know spit out these names without
cheating there's nicknames are there
well no that's that's that's not allowed
okay uh well some colleagues at
conferences have just called them anasta
or Freebo staff because they they didn't
want to learn the the phone number you
know I I get it phone number yeah and
these numbers are actually based on on
older sets of coordinates for these
Stars so they um yes the the minus in
the middle means that they're in the
southern hemisphere so negative is in
the southern hemisphere positive
and then uh 13 and 15 means that sort of
observable in the middle of the Year
okay so that's the deal with the
observation and where it was observed
yes yes but um have very different
stores both absolutely significant
career defining actually for for me but
really pushed pushed the envelope in in
very different ways so 80 1327 of 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 the big one and
the rest is nobody cares but to us it
proved that yes we can do it because one
astronomers live in a sort of way of you
know there are a lot of serendipitous
discoveries and we
that's really great but we need to show
that we can do it again reliably because
then then we're on to something it's not
just some kind of weird Quirk and there
are a lot of quirks in the universe but
we want to know is is that a real thing
does that happen regularly is there
something that we can learn right 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
um again working with a theorists of
course who run these Supernova models
is that so actually let me let me before
I get into this these two stars had huge
amounts of carbon relative to iron so we
usually use iron as a reference element
for what we call the metallicity so the
overall metal content the overall amount
of heavy elements in it so that's why
it's called iron deficiency that's right
so this does an incredibly iron
deficient which means there must be of
the second generation because
there was and interestingly enough
there was this discrepancy
a normal Supernova until then we thought
would get us so much iron
you know you would distribute that in
the gas cloud and then you would form
this little star that we're observing
but the iron abundance that we measured
was actually much lower than that and I
already mentioned you can't take things
away that must mean these early massive
pop three we call them population three
the first Stars
they must have exploded in a different
way than we previously thought they
can't output as much iron because
they just can't otherwise it wouldn't
match our observations got it and so
that's when we started to work with uh
several Theory groups
on on supernova yields so what comes out
of from the explosion of the Supernova
that's called Supernova yields and so
this one was not yielding much iron well
we needed to concoct a theoretical
Supernova that made less
and it's actually surprisingly difficult
because you can always add more in the
universe right but you can't take stuff
away so Japanese colleagues kind of came
up with the idea of a fainter Supernova
that just doesn't have a much is enough
oomph you know when it explodes so
somehow there's there's less iron coming
out but at the same time then these
Stars showed huge over bonuses of carbon
you know a thousand times more carbon
so how do you now get a thousand times
more carbon out of these poor first
supernovia that was the theoretical
Challenge and because we didn't have
just one star but two
um that really spurred the field to
think about what was the nature of the
first Stars how did they explode what
what are the implications because if
they are not as as luminous and bright
and energetic that has consequences for
for these early proto-galaxies in 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 the
earlier system to stay intact for longer
right so there's a whole tale of
consequences and this is what I mean
with we need to find the story because
you do you one thing and it's like The
Dominoes the consequences everywhere and
then you have a different Universe right
so what could possibly be a good
explanation for something that 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 the
official term what what was sort of as I
said cooked up in order to to explain
the observations and we have by the way
found a whole bunch more of these tasks
so that holds and it's called a fallback
mechanism so actually in in the uh
Supernova during the Supernova explosion
a massive um black hole emerges and so
some of the material falls back onto the
black hole so here is a a vacuum cleaner
now plopped into the middle right like a
temporary one that just cleans up
somewhere sort of right because if you
think of the we haven't talked about
this yet but um if you if you know what
a star looks like a master star looks
like on its on its in its interior
before it explodes
um you have hydrogen helium still on the
outskirts and then you have your layers
of heavier and heavy elements all the
way up to iron so you have an iron core
in the center
um
and because you can't get any energy out
of iron when you want to fuse to iron
atoms anymore right that's when the
Supernova explodes what occurs really
it's actually an implosion first and
then you have a balance of of the the
sort of neutron star phase that that
that occurs in the process and then it's
so awesome gets disrupted yeah it's like
this giant you know basketball
it all goes up explosion first explosion
yeah and so in the process right if you
make your black hole basically big
enough it will suck away some of the
iron because that's the closest in the
in terms of the layers you you you hold
on to it you don't let it escape and
carbon is much further out you let it
all go
and so so that explains why you can have
a big oomph and not much iron yield yes
yes so is this explain the he 1327
correct uh and others like it yes so
there's a there's a
well well established now that the lower
the iron abundance of the stars are the
higher the carbon sort of gets and
carbon is is such an interesting element
in that regard
if if we come back to the formation of
the first Lomas does right so we had the
the hotter gas just hydrogen helium that
made the first stars there were 100
solar masses or so because it could 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 lawmesters
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 lawmaster
we wouldn't be here today right and
we're carbon based and so I think carbon
is really the most important element in
the universe for for a variety of
reasons because it is just enabled this
whole Evolution that that we're 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 and develop humans and carbon is
kind of important in many ways yes yes
this is perhaps a
interesting tangent if I could just
mention that you interviewed a Mildred
dresselhaus carbon Queen
the remarkable life of the Nano size
Pioneer
um is there something you could say
about the magic of carbon and the magic
of Millie
well Millie was certainly magic
she was a professor at MIT for many
decades I 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
um she pioneered all sorts of carbon
um Nano work so she is a was a material
scientist
um very far removed from what I do on a
daily basis
um but yes carbon has amazing properties
when you study it and again that's
indeed another aspect of why carbon is
so fascinating
um not just in in the cosmos but also
for us you know making us creating us um
in the way that we can use it
um it's wonderful you sometimes think
about this chemical evolution
in this big philosophical way that we're
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 sore stuff yeah and it can go right I
mean it's almost like a cliche statement
but it's uh it's also uh a materials a
chemical a physics statement so it came
from hydrogen and helium
and somehow this formation has created
these 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 why do we get all this cool stuff
yeah that's that's a good question I
don't think it's a question as an answer
I keep just asking why no but it's uh
it's just this incredible mystery so
much cool stuff had to happen
so much sorry Hot Stuff had to happen
right and and so much could have gone
wrong and there would have been another
outcome you know and it's actually
amazing how 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 that was the
path maybe we would have ended up being
robots I don't know
um but it's it's it's certainly
wonderful to
you know a scientists for us to to help
contribute unraveling our our Cosmic
history right I alwa