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Hi, there.
My name is Michelle Thaller,
and I'm an astronomer at NASA's Goddard Space Flight Center.
And to me, one of the most amazing things about being an astronomer and studying
the universe are the stories that the universe has to tell us
about how things have changed over time and what our own place is in the universe.
I mean, everything we learn
about the stars, the galaxies, the beginning of the universe.
That's something that we are wrapped up inside of.
We are in that story.
And that's one of the most beautiful things I know of about science.
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What I want to do today is talk about a term
that's being used a lot because it's it's actually a major thing in astronomy.
One of the big questions right now, and that's something called the Cosmic Dawn,
and that sounds very beautiful and very dramatic.
And in fact, it is.
Simply put, this is a time that was the end of the cosmic Dark Ages.
I mean, already we've got these gorgeous storytelling terms.
One of the major goals of both the newly launched James Webb
Space Telescope and also the Nancy Grace Roman Space Telescope,
coming up in a few years,
is to study this era, this moment that we call the Cosmic Dawn.
And to give you an idea about why this is so important and what we're looking for.
One of the things you need to understand is that astronomers
really do have the ability to look into the past.
And I'm not talking about something that we calculate or make computer
simulations of or anything like that.
I'm talking about real images.
And the reason we can do that is there's a wonderful property to light.
It only travels at a certain speed.
Light travels very fast.
It travels at 186,000 miles per second.
But when you start dealing with the distances between stars and the galaxies,
this actually becomes a major thing you need to take into account.
You know, the nearest star’s already four light years away.
We see it four years in the past.
But then as soon as
you get out to the scale of the galaxies, things get very dramatic very quickly.
So the the nearest large galaxy to us, the Andromeda Galaxy,
is actually about 2 million light years away.
So if you take your binoculars out and you look at Andromeda in the sky tonight,
you will see it as the galaxy was 2 million years ago.
It took light that long to travel to you.
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So the Hubble Space Telescope
got very good at looking at galaxies farther and farther away.
And this is what the James Webb Space Telescope
and the Roman Space Telescope will continue.
And the amazing thing is that we have the ability now to build observatories
so powerful we can look back to a time
when the universe was very different than it is now.
And one of the things that kind of again, it really blows
my mind that this is real data, real measurements.
We did have two missions at NASA
that measured something called the microwave background radiation.
And this is radiation that comes from a time
when the universe was very, very different.
There were no stars, no planets.
And in fact, the entirety of the universe was just filled with very hot
hydrogen gas, a little bit of helium too, but mostly hot hydrogen gas.
And the gas was so hot it was actually glowing like the surface of the sun.
And that's the limit that we could actually see with any sort of telescope,
because after that, the universe is so hot and so dense light doesn't go through it.
And so that that's pretty much the limit. That was seen in microwaves,
and that was an observatory that took very, very big pixels on the sky,
you know, just sort of a general giant survey of all around us.
And we really can see back to a time when the universe was just glowing hot.
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That was about 400,000 years after the Big Bang.
And then something really amazing happened: the universe was still expanding
very quickly at this point, and it started to cool down very rapidly.
And so you went from this this very hot, glowing gas
in a fairly short amount of time things calm down.
It was expanding and cooling and it became cool enough
for the universe to form what we think of as atoms.
So let's talk about what have atoms so that this is sort of the basic
property of matter.
You have a nucleus inside that is composed of protons and neutrons,
very small particles, and then there are electrons that go around the nucleus.
They actually exist in an orbitals around the nucleus itself.
And so before that moment, you know, when the universe was still extremely hot,
these electrons were had so much energy that they were just flying around.
were going so fast that they couldn't be attracted by electric charge.
You know, there's a... protons have a positive charge,
electrons have a negative charge, they attract.
And so finally,
as these electrons begin to cool down and they weren't going so fast,
they were attracted to orbits around atoms.
And the first real atoms formed with a nucleus and electrons around it.
Now, that's really lovely.
The word we have for that as scientists
is neutral hydrogen.
It means it's not electrically charged.
The protons and electrons balance out and you have these wonderful, neutral,
stable atoms.
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It was during this time that gravity began
to bring together the hydrogen gas and actually make it into the first stars.
All you need is gravity.
Gravity brings stuff together.
There's a natural force that everything attracts together.
And then when you start compressing hydrogen gas together, more densely,
it actually goes way up in temperature until you get to a very hot temperature
that actually starts a star, a star is born.
And so we think that the first stars were forming, you know, on the order
you know, 1 to 200 million years after the big bang
when gravity had a chance to get this hydrogen all together.
This is an amazing mystery to us
in in science as to what this first generation of stars was like.
The only thing that we are absolutely sure of
is that they were very different than stars today.
They they may have been gigantic.
They may have been hundreds or thousands of times the mass of our sun,
they may not really have lived for very long at all.
They may not have been very stable.
They might have come together under the force of gravity,
ignited as a giant star
and then pretty much blown up in a giant supernova explosion.
So this first generation of stars and
and the first generation of galaxies that were forming around them.
And these stars now are organizing themselves into larger and larger
swarms and clusters.
That must have been a tremendously dramatic, volatile, you know,
part of the universe, I guess, sort of call it the
the party, the beginning of the universe.
It must have been spectacular.
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Now, the problem with
seeing it is let's go back to that, wonderful neutral gas now
that's filling in all the space between these young stars and young galaxies.
So the atoms, you know, have protons and neutrons
in the center and the electrons are in orbits
and there's a property of regular atoms is that they're actually very good
at absorbing light.
If you shine light through hydrogen gas and you have these wonderful whole atoms,
what happens is that the electrons actually absorb the light
and they use the energy of that light to jump to different orbits around the atom.
But basically that light goes away.
light shines on an atom.
Electrons take it, they absorb it, and they use it to move to different orbitals.
And so basically that stops the light.
And this is what we call the Cosmic Dark Ages.
And it's not that there's
anything horrible or creepy going on or anything like that,
it's just that the universe was in a state where the gas between the stars
and between these first forming galaxies was able to absorb light really well.
And that means it's hard to see.
It's hard to actually look back to that time
because we don't get much light coming from that time.
It's been absorbed by the gas that is existing everywhere between
the stars and galaxies.
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So then what happened to create this Cosmic Dawn?
Today we can see between the stars, between the galaxies quite well.
So something very, very fundamental changed about the nature of the universe.
And this really is what the Cosmic Dawn is: something heated up
the entirety of the universe, so that pretty much
all of the gas between the stars and galaxies lost electrons again.
Electrons got so much energy, they flew away
and now light was free to actually fly through the universe
without being absorbed by the hydrogen gas.
And this is the era of the Cosmic Dawn.
Now, the Cosmic Dawn is about the time when we think the first real galaxies
were forming, things were getting organized, stars were actually forming
these larger and larger structures.
These structures may have been forming clusters of galaxies.
You know, there's so much we want to learn about this time.
So what happened to actually heat up the entire universe?
And this is one of the big things we're trying to find out with the James Webb
Space Telescope and going on with missions like Roman, we're not exactly sure
what happened, what we think happened, and this is sort of the best idea
is that these giant stars, you know, these these stars that were hundreds
or thousands of times the mass of the Sun exploded immediately and left behind
big black holes, black holes that were, again,
probably hundreds of thousands of times the mass of the Sun.
And as the universe was a lot smaller back then, you know, there was actually less
volume. Gravity
attracted these black holes together into bigger and bigger black holes.
And so finally you had giant black holes, black holes
that were millions or billions of times the mass of the Sun.
In fact, we call these supermassive black holes.
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Black holes,
if there's matter falling into them,
you probably know a black hole is an object
that nothing can get out of, not even light.
But hot material sort of swirling around the black holes
can generate extreme temperatures and actually send off huge jets,
high energy jets that can actually extend for hundreds of thousands of light years
out into space, ripping apart any atom they come into contact with.
You know, the electrons are just gone.
So there was this time
when these these huge black holes were sending out these jets.
Like I said, remember, this is not coming from inside the black hole,
but from material swirling
around the black hole and these jets pointing every which way
in the sky, in the universe, basically ripped apart the neutral atoms
and all of a sudden light could fly freely through the universe.
We have actually been able
to look with Hubble pretty close back to this moment of the Cosmic Dawn.
And sure enough, we see giant black holes, black holes that are millions
or billions of times the mass of our Sun, but we're seeing them
when the universe was only about a billion years old.
And that's one of the huge mysteries to us, is, okay, have some idea
that maybe this first generation of gigantic stars formed huge black holes.
But even so, we don't really understand how you get a billion solar-mass
black hole when the universe less than a billion years old. Wow.
How did that happen?
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There are so many mysteries when it comes to this moment
of the Cosmic Dawn, the end of the cosmic Dark Ages.
And the things that I'm looking forward to, of course, is,
you know, seeing to the limit of this area where the universe becomes more opaque,
you know, difficult to see into.
it's not going to be as clean as just a single barrier.
I think there's going to be sort of tunnels
like it could be that there's a there's a big black hole that formed
when the universe was still neutral, when the gas could absorb light,
but there's a jet just coming right out in our direction.
And that jet was actually, you know, taking away all that neutral hydrogen.
And maybe there are places we can peer inside that
that wall of of neutral hydrogen gas that we can't see through.
So we may not be able to see to that moment when the first stars
turned on because of all that light absorbing hydrogen gas.
But I bet we can see pretty far back.
bet we will see the start of the first galaxies.
And maybe if we're really, really lucky, we'll be able to to peer into some bubble
where some of those first stars were busy heating up the gas around them.
And there's enough of a tunnel in there that we can actually see what's going on
and see what some of these very early-time stars were like.
So, think about what we're just about to do.
We've never seen the birth of the first stars.
We've never seen the birth of the very first galaxies,
because these things are obscured,
unfortunately, the universe was able to absorb light back then.
But with these telescopes, we're going to get right up to that edge.
And there may be bits and pieces where the neutral hydrogen is broken away
and we can see even farther and we will be able to see what happened
when the universe was only a few hundred million years old, you know, 500
million years old, something like that.
And that's incredible.
And that's something you can actually see with a space observatory.
You can take real data.
And it blows my mind
that we have this incredible privilege
to act... to watch the whole universe unfold because light only travels so fast.
The farther out we look, the more we can tell the story of where we came from.
And it's something that we know.
And to me, the things that are real, the real stories
the universe has to offer us,
that they pretty much blow everything that science fiction has away
I mean, I mean, I love science fiction, but, you know, when it came
to how those first stars came to being and how giant black holes
energized the entire universe and changed the way
the gas between the stars and galaxies work.
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This is a time that finally
we will have that next piece of the story as to where we came from.
And I think that is so beautiful and so dramatic.
So I'm looking forward to the next few years of of Webb.
I'm looking forward again to the Nancy Grace Roman Telescope after that.
And I'm looking forward to knowing even better where I came from
and where we all did, where we all came from, what the universe was like
when the very first stars and galaxies were forming.
So I hope that helps you understand a little bit more
what we mean by the Cosmic Dawn, the End of the Cosmic Dark Ages.
Again, I'm Michelle Thaller from Goddard Space Flight Center.
Thank you for listening.
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