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ANNA FREBEL: Have
you ever wondered

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how all the chemical
elements are made?

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Then join me as we are lifting
all the stardust secrets

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to understand the cosmic origin
of the chemical elements.

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We have come to the end
of our little journey

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where we wanted to explore
the origin of the chemical

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elements.

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[MUSIC PLAYING]

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I hope you enjoyed
it, and I hope

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I could help you to understand
that this is actually

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not just one origin.

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It's a whole process.

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And it's a process
that's still going on.

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So let's summarize
what we covered.

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Well, we talked a lot about
fusion and neutron capture

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processes that create all the
elements in the first place.

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We talked a little bit
about where that happens,

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I mean the cores of
stars, as well as

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in supernova and
neutron star mergers.

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And once these
elements are created,

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they can then be
observed, and they

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contribute to the chemical
evolution of the universe.

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If they are produced
in the early universe,

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then we can see them
in the older stars.

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So if produced in the
early universe, then

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we have this chance of
observing clean signatures.

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Today, that is not
possible anymore,

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because chemical evolution
has moved on too far.

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It's too messy today.

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And so, we use the most
metal poor stars in order

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to detect these
clean signatures,

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and to work with
nuclear physicists

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to understand how these
processes exactly work,

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and in what astrophysical
sites that might occur.

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So here we have
the oldest stars.

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And one reason why we can
infer that these stars must

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be very old, because
if there weren't we

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wouldn't get these
very clean signatures

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that were only present
at the earliest times.

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Now the very fortunate
coincidence for us,

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is that these older stars
actually found in the Milky Way

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today, so they are
fairly local objects.

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And that is a great advantage
over very distant galaxies

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that are also often used to
study the early universe.

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We find them in the
Milky Way, but we

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need the kind of
data, of course,

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to do a chemical analysis.

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And we do that with
spectroscopic observations.

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And we use the world's
largest telescopes for that,

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because only they can give
us the kind of data quality

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that we need in order to measure
these tiny little absorption

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lines that tell us about
the composition of all

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the different elements
across the periodic table.

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And then finally, if we
put this all together,

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we can determine the chemical
composition of our old stars,

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and actually we can do
so not just of old stars,

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but of stars at a
variety of ages,

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a variety of metal contents.

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And that helps us
to piece together

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how the amount of each metal
actually changed with time.

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And that's a very
exciting prospect.

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So that's chemical evolution.

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And as I mentioned before,
this is an ongoing process.

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Much of all the elements
are still being produced.

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right now.

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There's probably a supernova
going off right now

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as we speak somewhere
in the universe

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where more elements
have been created.

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And so, the chemical makeup of
the universe is changed again.

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So it's continuously
changing process.

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And that brings us to the end.

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So this is really all the star
stuff that we are made of.

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And while the origin
is not entirely

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stars, but also stellar
remnants, as I mentioned,

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supernova and
neutron star mergers

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should be included in that.

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But, yeah, that is
really our cosmic origin.

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And as humans, it lays in the
cosmos, in the cosmic objects,

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in a variety of them.

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And it takes a whole
bunch of processes

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in order to unravel that
all those stardust secrets.

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And one last thing
I wanted to mention,

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doing this kind of work with
all the different elements

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has shown pretty clearly
that carbon is not only

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the most important
elements for us humans,

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because all lifeforms
are carbon based.

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It actually turns out, it's
also the most important element

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in the universe, because
at that early time

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it needed the carbon
to help for the gas

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to come together to form small
stars in small structures.

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And so, I think carbon really
plays the most fundamental role

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in the universe that
we can think of,

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because it helps star
formation and galaxy

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formation, and ultimately
planet formation,

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and formation of life.

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[MUSIC PLAYING]