WEBVTT FILE

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[Music]

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Hi, there.

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My name is Michelle Thaller,

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and I'm an astronomer at NASA's
Goddard Space Flight Center.

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And to me, one of the most amazing things
about being an astronomer and studying

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the universe are the stories
that the universe has to tell us

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about how things have changed over time
and what our own place is in the universe.

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I mean, everything we learn

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about the stars, the galaxies,
the beginning of the universe.

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That's something that we are wrapped up
inside of.

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We are in that story.

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And that's one of the most
beautiful things I know of about science.

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[Music]

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What I want to do
today is talk about a term

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that's being used a lot because it's it's
actually a major thing in astronomy.

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One of the big questions right now, and
that's something called the Cosmic Dawn,

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and that sounds very beautiful
and very dramatic.

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And in fact, it is.

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Simply put, this is a time
that was the end of the cosmic Dark Ages.

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I mean, already we've got these gorgeous
storytelling terms.

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One of the major goals of
both the newly launched James Webb

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Space Telescope and also the Nancy Grace
Roman Space Telescope,

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coming up in a few years,

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is to study this era, this moment
that we call the Cosmic Dawn.

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And to give you an idea about why this is
so important and what we're looking for.

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One of the things you need to understand
is that astronomers

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really do
have the ability to look into the past.

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And I'm not talking about something
that we calculate or make computer

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simulations of or anything like that.

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I'm talking about real images.

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And the reason we can do that
is there's a wonderful property to light.

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It only travels at a certain speed.

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Light travels very fast.

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It travels at 186,000 miles per second.

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But when you start dealing with the
distances between stars and the galaxies,

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this actually becomes a major thing
you need to take into account.

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You know, the nearest star’s already
four light years away.

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We see it four years in the past.

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But then as soon as

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you get out to the scale of the galaxies,
things get very dramatic very quickly.

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So the the nearest large galaxy
to us, the Andromeda Galaxy,

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is actually about 2 million
light years away.

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So if you take your binoculars out and
you look at Andromeda in the sky tonight,

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you will see it
as the galaxy was 2 million years ago.

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It took light that long to travel to you.

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[Music]

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So the Hubble Space Telescope

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got very good at looking at galaxies
farther and farther away.

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And this is what the James Webb
Space Telescope

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and the Roman Space Telescope
will continue.

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And the amazing thing is that we have
the ability now to build observatories

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so powerful we can look back to a time

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when the universe
was very different than it is now.

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And one of the things that kind of again,
it really blows

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my mind that this is real data,
real measurements.

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We did have two missions at NASA

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that measured something
called the microwave background radiation.

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And this is radiation
that comes from a time

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when the universe was very,
very different.

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There were no stars, no planets.

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And in fact, the entirety of the universe
was just filled with very hot

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hydrogen gas, a little bit of helium too,
but mostly hot hydrogen gas.

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And the gas was so hot it was actually
glowing like the surface of the sun.

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And that's the limit that we could
actually see with any sort of telescope,

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because after that, the universe is so hot
and so dense light doesn't go through it.

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And so that that's pretty much the limit.
That was seen in microwaves,

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and that was an observatory that took
very, very big pixels on the sky,

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you know, just sort of a general giant
survey of all around us.

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And we really can see back to a time
when the universe was just glowing hot.

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[Music]

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That was about 400,000 years after the Big Bang.

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And then something really amazing happened:
the universe was still expanding

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very quickly at this point,
and it started to cool down very rapidly.

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And so you went from this
this very hot, glowing gas

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in a fairly short amount of time things
calm down.

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It was expanding and cooling
and it became cool enough

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for the universe to form
what we think of as atoms.

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So let's talk about what have atoms
so that this is sort of the basic

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property of matter.

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You have a nucleus inside
that is composed of protons and neutrons,

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very small particles, and then there are
electrons that go around the nucleus.

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They actually exist in an orbitals
around the nucleus itself.

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And so before that moment, you know,
when the universe was still extremely hot,

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these electrons were had so much energy
that they were just flying around.

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were going so fast that they couldn't
be attracted by electric charge.

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You know,
there's a... protons have a positive charge,

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electrons have a negative charge,
they attract.

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And so finally,

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as these electrons begin to cool down
and they weren't going so fast,

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they were attracted to orbits
around atoms.

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And the first real atoms formed with
a nucleus and electrons around it.

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Now, that's really lovely.

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The word we have for that as scientists

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is neutral hydrogen.

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It means it's not electrically charged.

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The protons and electrons balance out
and you have these wonderful, neutral,

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stable atoms.

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[Music]

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It was during this time that gravity began

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to bring together the hydrogen gas
and actually make it into the first stars.

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All you need is gravity.

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Gravity brings stuff together.

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There's a natural force
that everything attracts together.

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And then when you start compressing
hydrogen gas together, more densely,

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it actually goes way up in temperature
until you get to a very hot temperature

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that actually starts a star, a star is born.

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And so we think that the first stars
were forming, you know, on the order

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you know, 1 to 200 million years
after the big bang

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when gravity had a chance
to get this hydrogen all together.

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This is an amazing mystery to us

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in in science as to what
this first generation of stars was like.

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The only thing that we are absolutely
sure of

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is that they were very different
than stars today.

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They they may have been gigantic.

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They may have been hundreds
or thousands of times the mass of our sun,

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they may not really have lived
for very long at all.

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They may not have been very stable.

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They might have come together
under the force of gravity,

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ignited as a giant star

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and then pretty much blown up in a giant
supernova explosion.

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So this first generation of stars and

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and the first generation of galaxies
that were forming around them.

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And these stars now are organizing
themselves into larger and larger

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swarms and clusters.

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That must have been a tremendously
dramatic, volatile, you know,

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part of the universe,
I guess, sort of call it the

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the party, the beginning of the universe.

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It must have been spectacular.

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[Music]

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Now, the problem with

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seeing it is let's go back to that,
wonderful neutral gas now

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that's filling in all the space between
these young stars and young galaxies.

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So the atoms, you know, have protons
and neutrons

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in the center
and the electrons are in orbits

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and there's a property of regular atoms
is that they're actually very good

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at absorbing light.

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If you shine light through hydrogen gas
and you have these wonderful whole atoms,

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what happens is that the electrons
actually absorb the light

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and they use the energy of that light to
jump to different orbits around the atom.

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But basically that light goes away.

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light shines on an atom.

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Electrons take it, they absorb it, and
they use it to move to different orbitals.

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And so basically that stops the light.

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And this is what we call
the Cosmic Dark Ages.

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And it's not that there's

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anything horrible or creepy
going on or anything like that,

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it's just that the universe was in a state
where the gas between the stars

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and between these first forming galaxies
was able to absorb light really well.

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And that means it's hard to see.

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It's hard
to actually look back to that time

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because we don't get much light
coming from that time.

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It's been absorbed by the gas
that is existing everywhere between

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the stars and galaxies.

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[Music]

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So then what happened to create this
Cosmic Dawn?

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Today we can see between the stars,
between the galaxies quite well.

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So something very, very fundamental
changed about the nature of the universe.

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And this really is what the Cosmic Dawn is:
something heated up

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the entirety of the universe,
so that pretty much

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all of the gas between the stars
and galaxies lost electrons again.

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Electrons got so much energy,
they flew away

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and now light was free to actually fly
through the universe

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without being absorbed
by the hydrogen gas.

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And this is the era of the Cosmic Dawn.

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Now, the Cosmic Dawn is about the time
when we think the first real galaxies

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were forming, things were getting
organized, stars were actually forming

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these larger and larger structures.

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These structures may have been
forming clusters of galaxies.

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You know, there's so much
we want to learn about this time.

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So what happened to actually heat up
the entire universe?

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And this is one of the big things
we're trying to find out with the James Webb

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Space Telescope and going on with missions
like Roman, we're not exactly sure

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what happened, what we think happened,
and this is sort of the best idea

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is that these giant stars, you know, these
these stars that were hundreds

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or thousands of times the mass of the Sun
exploded immediately and left behind

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big black holes, black holes
that were, again,

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probably hundreds of thousands of times
the mass of the Sun.

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And as the universe was a lot smaller back
then, you know, there was actually less

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volume. Gravity

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attracted these black holes together
into bigger and bigger black holes.

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And so finally you had giant black holes,
black holes

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that were millions or billions of times
the mass of the Sun.

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In fact,
we call these supermassive black holes.

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[Music]

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Black holes,

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if there's matter falling into them,

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you probably know
a black hole is an object

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that nothing can get out of,
not even light.

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But hot material
sort of swirling around the black holes

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can generate extreme temperatures
and actually send off huge jets,

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high energy jets that can actually extend
for hundreds of thousands of light years

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out into space, ripping apart any atom
they come into contact with.

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You know, the electrons are just gone.

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So there was this time

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when these these huge black holes
were sending out these jets.

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Like I said, remember, this is not coming
from inside the black hole,

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but from material swirling

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around the black hole
and these jets pointing every which way

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in the sky, in the universe,
basically ripped apart the neutral atoms

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and all of a sudden light
could fly freely through the universe.

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We have actually been able

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to look with Hubble pretty close
back to this moment of the Cosmic Dawn.

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And sure enough, we see giant black holes,
black holes that are millions

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or billions of times the mass of our Sun,
but we're seeing them

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when the universe
was only about a billion years old.

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And that's one of the huge mysteries
to us, is, okay, have some idea

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that maybe this first generation
of gigantic stars formed huge black holes.

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But even so, we don't really understand
how you get a billion solar-mass

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black hole when the universe
less than a billion years old. Wow.

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How did that happen?

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[Music]

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There are so many
mysteries when it comes to this moment

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of the Cosmic Dawn,
the end of the cosmic Dark Ages.

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And the things that I'm looking forward
to, of course, is,

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you know, seeing to the limit of this area
where the universe becomes more opaque,

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you know, difficult to see into.

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it's not going to be as clean
as just a single barrier.

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I think there's going to be
sort of tunnels

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like it could be that there's a
there's a big black hole that formed

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when the universe was still neutral,
when the gas could absorb light,

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but there's a jet just coming
right out in our direction.

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And that jet was actually, you know, taking away
all that neutral hydrogen.

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And maybe there are places
we can peer inside that

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that wall of of neutral hydrogen gas
that we can't see through.

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So we may not be able to see
to that moment when the first stars

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turned on because of all that light
absorbing hydrogen gas.

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But I bet we can see pretty far back.

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bet we will see
the start of the first galaxies.

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And maybe if we're really, really lucky,
we'll be able to to peer into some bubble

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where some of those first stars were busy
heating up the gas around them.

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And there's enough of a tunnel in there
that we can actually see what's going on

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and see what some of these very early-time
stars were like.

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So, think about what
we're just about to do.

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We've never seen the birth
of the first stars.

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We've never seen the birth
of the very first galaxies,

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because these things are obscured,

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unfortunately, the universe was able
to absorb light back then.

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But with these telescopes,
we're going to get right up to that edge.

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And there may be bits and pieces where the
neutral hydrogen is broken away

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and we can see even farther
and we will be able to see what happened

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when the universe was only a few hundred
million years old, you know, 500

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million years old, something like that.

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And that's incredible.

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And that's something you can actually see
with a space observatory.

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You can take real data.

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And it blows my mind

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that we have this incredible privilege

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to act... to watch the whole universe unfold
because light only travels so fast.

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The farther out we look, the more we can
tell the story of where we came from.

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And it's something that we know.

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And to me, the things that are real,
the real stories

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the universe has to offer us,

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that they pretty much blow
everything that science fiction has away

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I mean, I mean, I love science
fiction, but, you know, when it came

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to how those first stars came to being
and how giant black holes

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energized the entire universe
and changed the way

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the gas between
the stars and galaxies work.

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[Music]

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This is a time that finally

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we will have that next piece of the story
as to where we came from.

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And I think that is so beautiful
and so dramatic.

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So I'm looking forward
to the next few years of of Webb.

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I'm looking forward again to the Nancy
Grace Roman Telescope after that.

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And I'm looking forward to knowing
even better where I came from

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and where we all did, where we all came
from, what the universe was like

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when the very first stars
and galaxies were forming.

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So I hope that helps
you understand a little bit more

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what we mean by the Cosmic Dawn,
the End of the Cosmic Dark Ages.

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Again, I'm Michelle Thaller
from Goddard Space Flight Center.

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Thank you for listening.

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[Music fades out]