All language subtitles for How the Universe Works s01e03 Galaxies.eng

We live in a galaxy
called the Milky Way,

an empire with
hundreds of billions of stars.

How did we get here,
and what's our future?

In every way, those questions
involve galaxies.

There are 200 billion
galaxies in the known universe,

each one unique, enormous,
and dynamic.

Galaxies are violent.

They were born
in a violent history.

They will die a violent death.

Where do galaxies come from?

How do they work?
What is their future?

And how will they die?

This is our galaxy,
the Milky Way.

It's around
12 billion years old.

The galaxy itself is a huge disk

with giant spiral arms
and a bulge in the middle.

It's just one of a huge number
of galaxies in the universe.

Galaxies are,
first and foremost,

large collections of stars.

The average galaxy
may contain 100 billion stars.

They're really
stellar nurseries,

the place where stars are born
and where they also die.

The stars in a galaxy are born

in clouds of dust and gas
called nebulas.

These are the pillars
of creation in the Eagle nebula,

a star nursery
deep in the Milky Way.

Our galaxy contains
many billions of stars,

and around many of them

are systems
of planets and moons.

But for a long time, we didn't
know much about galaxies.

Just a century ago,

we thought that the Milky Way
was all there was.

Scientists called it
our island universe.

For them,
no other galaxies existed.

Then, in 1924, astronomer
Edwin Hubble changed all that.

Hubble was observing
the universe

with the most advanced telescope
at the time,

the 100-inch Hooker on
Mount Wilson near Los Angeles.

Deep in the night sky,

he saw fuzzy blobs of light
that were far, far away.

He realized they weren't
individual stars at all.

They were
whole cities of stars...

galaxies
way beyond the Milky Way.

Astronomers
had an existential shock.

In one year,

we went from the universe
being the Milky Way galaxy

to a universe
of billions of galaxies.

Hubble had made
one of the greatest discoveries

in the history of astronomy...

the universe contains

not just one
but a great number of galaxies.

This is the Whirlpool galaxy.

It has two giant spiral arms

and contains
around 160 million stars.

And Galaxy M87,
a giant elliptical galaxy...

it's one of the oldest
in the universe,

and the stars glow gold.

And this is the Sombrero galaxy.

It has a huge, glowing core

with a ring of gas and dust
all around it.

Galaxies are gorgeous.

They represent, in some sense,

the basic unit
of the universe itself.

They're like gigantic pinwheels
twirling in outer space.

It's like fireworks
created by Mother Nature.

Galaxies are big...
really, really big.

On Earth,
we measure distance in miles.

In space,
astronomers use light-years...

The distance light travels
in a year.

That's just under
6 trillion miles.

Here we are,

25,000 light-years away
from the center of our galaxy,

and our galaxy is over
100,000 light-years across.

But even that,
as large as it is,

is kind of a speck
in the cosmic-distance scale.

Our Milky Way galaxy
may seem big to us,

but compared to some others
out there...

...it's actually pretty small.

Andromeda,
our nearest galactic neighbor,

is over 200,000
light-years across...

twice the size of the Milky Way.

M87 is the largest
elliptical galaxy

in our own cosmic backyard,
and much bigger than Andromeda.

But M87 is tiny
compared to this giant.

6 million light-years across,

IC 1011 is the biggest galaxy
ever found.

It's 60 times larger
than our Milky Way.

We know galaxies are big
and they're everywhere,

but why is that?

One of the very big questions

we have in astrophysics
is where galaxies come from.

We really don't have a complete
understanding of that.

The universe started
in what we call a Big Bang,

an extremely hot
and extremely dense phase

about 13.7 billion years ago.

We know that nothing
like a galaxy could have existed

at that time.

So galaxies must have been born,
they must have formed,

out of that very early universe.

It takes gravity to make stars

and even more gravity to pull
stars together into galaxies.

The first stars formed

just 200 million years
after the Big Bang.

Then gravity
pulled them together,

building the first galaxies.

The Hubble Space Telescope has
allowed us to peer back in time

to almost the dawn of time...

...the period when galaxies
have just begun to form.

The Hubble sees
lots of galaxies.

But the light we see today
from those galaxies

left there thousands, millions,
even billions of years ago.

It's taken all that time
to reach us,

so what we see today

is the ancient history
of those galaxies.

When we look
at the Hubble Deep Field,

what we see are little smudges.

They don't look much like
the galaxies we see today.

They're just
little smudges of light

that we can barely discern.

Those smudges of light contain
millions or billions of stars

that have just begun
to merge together.

These faint smudges

are the earliest galaxies
of all.

They were formed

around one billion years after
the beginning of the universe.

But that's as far back
as Hubble can see.

If we want
to go even further back in time,

we need a different kind
of telescope...

one too big
to launch into space.

Well, now we have one, in the
high desert of northern Chile.

This is ACT,
the Atacama Cosmology Telescope.

At 17,000 feet,

it's the highest ground-based
telescope in the world.

I really like working

in the extreme environment
of ACT.

It's very, very cold often,
and the wind blows violently.

But the good thing about it
from our point of view

is that the sky is very,
very clear almost all the time.

Clear skies are important

for ACT's precise mirrors to
focus on the earliest galaxies.

With ACT, we're able to zoom in
with unprecedented detail

on parts of the sky.

We can also study the progress
of growth of structures,

where structures
are things like galaxies

and clusters of galaxies,

with a very fine-scale detail.

ACT doesn't detect
visible light.

It detects cosmic microwaves
from the time

the universe was just a few
hundred thousand years old.

The telescope not only detects
early galaxies...

it actually sees how they grew.

We're able to track the progress

of the formations of galaxies
and clusters of galaxies.

We see the footprints of all
the galaxies that have grown

in the time between
when the universe was

a few hundred thousand
years old till now.

ACT has helped
astronomers understand

how galaxies have evolved

since almost
the beginning of time itself.

And we can start
answering the question,

what did galaxies look like
when they were young?

How did they compare
with modern-day galaxies?

How have they grown?

Astronomers are seeing
how galaxies evolve

from groups of stars

into the patchwork of systems
we see today.

Our current understanding
is that stars form clusters

that build into galaxies

that build
into clusters of galaxies

that build
into superclusters of galaxies,

the largest structures we
observe in the universe today.

Early galaxies were a mess...

lumpy bunches
of stars, gas, and dust.

But today
galaxies look neat and orderly.

So, how do messy galaxies
transform

into beautiful spirals
and pinwheels?

The answer is gravity.

Gravity shapes galaxies
and controls their future.

There is
an unimaginably powerful

and incredibly destructive
source of gravity

at the heart of most galaxies.

And there's one buried
deep at the center

of our own Milky Way.

Galaxies have existed
for over 12 billion years.

We know
these vast empires of stars

come in all shapes and sizes,

from swirling spirals
to huge balls of stars.

But there's still a lot
about galaxies we don't know.

How did galaxies come to have
the shapes they do?

Was a spiral galaxy
always a spiral galaxy?

The answer
is almost certainly no.

Very young galaxies
are messy and chaotic,

a jumble
of stars, gas, and dust.

Then, over billions of years,

they evolve
into neat, organized structures,

like the Whirlpool galaxy...

Or our own Milky Way.

Our Milky Way began not as
a single baby galaxy, but many.

What is now our Milky Way

was once comprised
of lots of small structures,

irregularly shaped objects
that began to merge.

The thing that pulls
the small structures together

is gravity.

Gradually,
it pulls stars inward.

They begin spinning
faster and faster

and flatten into a disk.

Stars and gas are swept

into huge spiral arms.

This process was repeated
billions and billions of times

across the universe.

Each of these galaxies
looks different,

but they do have
one thing in common...

they all seem to orbit
something at their center.

For years, scientists wondered

what could be powerful enough
to change how a galaxy behaves.

They found out... a black hole.

And not just
any kind of black hole...

a supermassive black hole.

The first clue that supermassive
black holes existed

was that at the heart
of some galaxies,

there was
an immense amount of energy

emanating out from the center.

What we're seeing is the black
holes in these galaxies

feasting on the material
around them,

so it's like having
a huge Thanksgiving dinner.

The meal is gas and stars,

and it's being eaten
by the supermassive black hole.

When black holes eat,
they sometimes eat too fast

and spit their dinner
back out into space

in beams of pure energy.

It's called a quasar.

When scientists see a quasar
blasting from a galaxy,

they know it has
a supermassive black hole.

But what about our galaxy?
There's no quasar here.

Does that mean there's
no supermassive black hole?

Andrea Ghez and her team

have spent the last 15 years
trying to find out.

So, the key to discovering

a supermassive black hole
at the center of our Milky Way

is to watch how the stars move.

The stars move
because of the gravity,

just like the planets
orbiting the Sun.

But the stars closest
to the center of the galaxy

are hidden by clouds of dust.

So Ghez used the giant
Keck telescope in Hawaii

to look through the clouds.

What she saw was a strange
and brutal place.

Everything is more extreme

at the center of our galaxy.

Things move really fast.

Stars are gonna be
whizzing by one another.

It's windy.
It's violent.

It's unlike
anyplace else in our galaxy.

Ghez and her team
began to take pictures

of a few stars
orbiting near the center.

The task has been
to make a movie

of the stars at the center,

and so you have to be patient,

because you take a picture,
and then you take another one,

and you see it move.

The pictures
of the orbiting stars

revealed something amazing.

They were moving at
several million miles an hour.

When we had the second picture

was the most exciting point
in this experiment,

because it was clear to us that
these stars were moving so fast

that the supermassive-black-hole
hypothesis had to be right.

And it was right.

Ghez and her team tracked
the movement of the stars

and pinpointed
what they were orbiting.

There's only one thing
powerful enough

to sling big stars around
like that...

a supermassive black hole.

It's the gravity
of the supermassive black hole

that makes these stars orbit,

so the curvature
was the definitive proof

of a supermassive black hole
at the center of our galaxy.

The black hole
at the center of the Milky Way

is gigantic...
15 million miles across.

So, is Earth in any danger?

We are in absolutely no danger

of being sucked into
our supermassive black hole.

It's simply too far away.

In fact, the Earth
is 25,000 light-years away

from the supermassive black hole
at the center of the Milky Way.

That's many trillions of miles.

The Earth is safe... for now.

Supermassive black holes may be

the source
of huge amounts of gravity,

but they don't have enough power
to hold galaxies together.

In fact, according to
the laws of physics,

galaxies should fly apart.

So why don't they?

Because there's something
out there

even more powerful
than a supermassive black hole.

It can't be seen, and it's
virtually impossible to detect.

It's called dark matter,
and it's everywhere.

Astronomers have figured out

that supermassive black holes
live at the heart of galaxies

and pull stars
at incredible speeds.

But they're not strong enough

to hold all the stars
in a gigantic galaxy together.

So, what does
hold them together?

It was a mystery

until a maverick scientist
came up with the idea

that something unknown
was at work.

Back in the 1930s,
Swiss astronomer Fritz Zwicky

wondered why galaxies
stayed together in groups.

By his calculations, they didn't
generate enough gravity,

so they should fly
away from each other.

And so he said, "Well, I know
that they haven't flown apart.

I see them all gathered together
in this nice collection.

Therefore, something
must be holding them in place."

But our own gravity
was just not strong enough.

And so he concluded

that it must be something which
nobody had detected before,

nobody had thought about,

and he gave it this
name, dark matter.

And this is really
a stroke of genius.

Fritz Zwicky
was decades ahead of his time,

and that's why he grated
on the astronomical community.

But, you know, he was right.

If what Zwicky called
dark matter

held galaxies together
in groups,

perhaps it also holds
individual galaxies together.

To find out, scientists built
virtual galaxies in computers

with virtual stars
and virtual gravity.

We did a simulation

where we put a lot of particles
in orbit in a flat disk,

which was just like
the picture of our galaxy.

And we expected to find that
we get a perfectly good galaxy,

and we were looking to see
if it had a spiral or whatnot.

But we found
it always came apart.

There just wasn't
enough gravity in the galaxy

to hold it together.

So Ostriker then added
extra gravity,

from virtual dark matter.

It seemed like
a natural thing to try.

And it solved the problem.
It fixed it.

Gravity from dark
matter held the galaxy together.

Dark matter acts

as a sort of protective
scaffolding for galaxies

that really holds them up
and holds them in place

and prevents them
from falling apart.

Now scientists are discovering

that dark matter doesn't just
hold galaxies together...

it might have sparked them
into life.

We think
that dark matter was created

out of the Big Bang,

and dark matter began to clump,

and these clumpings
of dark matter

eventually became the nuclei,
the seeds, for our galaxy.

But scientists
still have no idea

what dark matter actually is.

Dark matter is weird because
we don't understand it at all.

It's clearly
not made of the same stuff

that you and I are made of.

You can't push against it.
You can't feel it.

Yet it's probably all around us.

It's a ghostlike material

that will pass right through you
as if you didn't exist at all.

We might not know
much about dark matter,

but the universe is full of it.

So, the dark matter,
weight-for-weight,

makes up at least six times
as much of the universe

as does normal matter, the stuff
that we're all made from.

And without it,

the universe just wouldn't work
the way that it seems to work.

But the universe does work,

so maybe dark matter is real.

Strange stuff,

and recently, it's been detected
in deep space...

not directly but by observing
what it does to light.

It bends it in a process
called gravitational lensing.

Gravitational lensing
really allows us to test

the presence of dark matter.

And the way that works is that,

as a beam of light
from some distant galaxy

is traveling towards us,

if it passes by a large
collection of dark matter,

its path will be deflected
around that dark matter

by the gravitational pull.

When the
Hubble telescope looks

deep into the universe,

some galaxies do seem
distorted and stretched.

That's caused by the dark
matter, which warps the image.

It's sort of like
looking through a goldfish bowl.

By probing
the shapes of those galaxies

and the degree of distortion,

we can really measure
very accurately

the amount of dark matter
that's there.

It's clear now

that dark matter is a vital
ingredient of the universe.

It's been working
since the dawn of time

and affects
everything everywhere.

It triggers
the birth of galaxies

and keeps them
from falling apart.

We can't see it or detect it,

but, nevertheless, dark matter
is the master of the universe.

Galaxies look isolated.

It's true... they are
trillions of miles apart.

But, actually, they live
in groups called clusters.

And these clusters of galaxies
are linked together

in superclusters, containing
tens of thousands of galaxies.

So, where does
our Milky Way galaxy fit in?

If you take a look
at the big picture,

you realize that our galaxy

is part of a local group
of galaxies, perhaps 30,

and our galaxy and Andromeda

are the two biggest galaxies
in this local group.

But if you look
even farther out,

we are part of the
Virgo supercluster of galaxies.

Scientists are now mapping

the overall structure
of the universe

and the position of clusters
and superclusters of galaxies.

This is Apache Point
Observatory in New Mexico,

home to the Sloan
Digital Sky Survey, or SDSS.

It's a small telescope
with a big price tag,

and it has a unique mission.

SDSS is building the first
3-D map of the night sky,

a process that's identifying
the exact positions

of tens of millions of galaxies.

To do it,
SDSS goes galaxy hunting

way out into space,
far beyond our Milky Way.

It pinpoints
the positions of galaxies,

and this information is copied
onto aluminum disks.

These aluminum disks
are about 30 inches across,

and they have 640 holes each,

and these holes correspond

to the objects of interest
in the sky.

Each object is a galaxy.

Light from the galaxy
is channeled through a hole

and down a fiberoptic cable.

This method records data
on distance and position

from thousands of galaxies
and plots their location in 3-D.

It's telling us
about their shape.

It's telling us
about their makeup.

It's telling us
how they're distributed.

And all of this
is very important

to astronomy
and understanding our universe.

And this
is what they're creating...

the biggest 3-D map ever.

The map is showing us things
we've never seen before.

It shows galaxies
in clusters and superclusters...

But pull back even more,

and we see that these
superclusters are connected

into structures
called filaments.

SDSS has found one

that's 1.4 billion
light-years across.

It's called
the Great Sloan Wall,

and it's
the largest single structure

ever discovered
in the history of science.

You get a sense that
you are in something quite vast.

You can see
the clusters and filaments

as the data would scroll by.

And, you know, each one
of these little, fuzzy spots

were actually galaxies...
not stars but galaxies...

and so you're seeing
whole clusters of these things.

SDSS is showing
galactic geography

on a vast scale.

Scientists have taken it
even further.

They've built the whole universe
in a supercomputer.

Here you can't see
individual galaxies.

You can't even see
galaxy clusters.

What you can see
are superclusters,

linked together on filaments
in a vast cosmic web.

As one begins to come back

from the whole scale
of the universe,

one begins to reveal
a filamentary pattern,

a cosmic web
containing galaxies

and clusters of galaxies
that light up the universe

where there are as many
galaxies in that direction

as that direction as that
direction as that direction.

And, in fact, on larger scales,

the universe
kind of looks like a sponge.

Each of the filaments is home

to millions of galaxy clusters,

all bound together
by dark matter.

In this computer simulation,

the dark matter glows
along the filaments.

Dark matter affects where in
the universe galaxies will form.

When we look at galaxies,

they're not sprinkled around
at random.

They actually tend to form
in little groups,

and that's really reflecting

the large-scale distribution
of dark matter.

Dark matter is the glue

holding together the whole
superstructure of the universe.

It binds galaxies in clusters

and clusters in superclusters.

All these are locked together
in a web of filaments.

Without dark matter,

the whole structure
of the universe

would simply fall apart.

This is the big picture
of our universe.

It's a giant cosmic web.

And hidden deep in one of these
filaments is the Milky Way.

It's been around
for nearly 12 billion years.

But in the future,

it's going to be destroyed
in a gigantic cosmic collision.

Galaxies
are vast kingdoms of stars.

Some are giant balls,

and others, complex spirals.

The thing is,
they never stop changing.

While it may seem,
when we look out at our galaxy,

that our galaxy is static
and been here forever, it's not.

Our galaxy is a dynamic place.

Its very nature has been
changing over cosmic time.

Galaxies not only
change... they move, as well.

And sometimes
they run into each other.

And when they do,
it's eat or be eaten.

There's a zoo of galaxies
that you can find out there,

and this entire zoo
can interact or collide

with any of the other members
of the zoo.

This is NGC 2207.

It looks like an enormous
double-spiral galaxy,

but it's actually
two galaxies colliding.

The collision will last
millions of years,

and eventually the two galaxies
will become one.

Collisions like this happen
all over the universe.

Our own Milky Way
is no exception.

The Milky Way is, in fact,
a cannibal,

and it exists
in its present form

by having cannibalized
small galaxies

that it literally ate up.

And today we can see
small streams of stars

that are left over
from the most recent mergers

that have formed
the Milky Way galaxy.

But that's nothing
compared to what's coming up.

We are on a collision course
with the galaxy Andromeda.

And for the Milky Way,
that's bad news.

Our Milky Way galaxy
is approaching Andromeda

at the rate of about a quarter
of a million miles per hour,

which means that in 5 billion
to 6 billion years,

it's all over
for the Milky Way galaxy.

You would see
the entire Andromeda galaxy

speeding towards us, really
barreling straight into us.

As the two galaxies interact,

they both become
more and more disturbed

and closer and closer together.

And the whole process
starts to snowball.

The two galaxies
will enter a death dance.

This is a simulation
of the future collision,

sped up millions of times.

As the galaxies crash together,

clouds of gas and dust are
thrown out in all directions.

Gravity
from the merging galaxies

rips stars from their orbits
and shoots them deep into space.

As we approach doomsday

for the Milky Way galaxy,
it would be spectacular.

We would have a front-row seat

on the destruction
of our own galaxy.

And eventually, the two galaxies
will go right through each other

and then come back
and then coalesce.

It's strange, but the
stars themselves won't collide.

They're still too far apart.

All of the stars are basically

just gonna pass
right by each other.

The probability
of one individual star

hitting another individual star
are basically zero.

However, the gas
and dust between the stars

will start to heat up.

Eventually, it ignites,

and the clashing galaxies
will glow white-hot.

So, at a certain point,
the sky could be on fire.

The Milky Way and Andromeda as
we know it will cease to exist,

and Milkomeda will be born,

and it will look like
a whole new galaxy.

This new galaxy, Milkomeda,

will become
a huge, elliptical galaxy

without any arms
or spiral shape.

There's no escaping
what's going to happen.

The question is,
what's it mean for planet Earth?

We may either be
thrown out into outer space

when the arms of the Milky Way
galaxy are ripped apart,

or we could wind up in
the stomach of this new galaxy.

Stars and planets will
be pushed all over the place,

so this may well be
the end of planet Earth.

Galaxies all over the universe
will continue to collide.

But this age
of galactic cannibalism

will eventually pass...

Because there is
an even more destructive force

in the universe,

a force that nothing can stop.

It will ultimately push galaxies
away from each other,

stretching everything,
until the universe...

Rips itself apart.

Galaxies are home

to stars, solar systems,
planets, and moons.

Everything that's important
happens in galaxies.

Galaxies are
the lifeblood of the universe.

We arose
because we live in a galaxy,

and everything we can see

and everything that matters
to us in the universe

happens within galaxies.

But the truth is,

galaxies are delicate structures
held together by dark matter.

Now scientists have found
another force

at work in the universe.

It's called dark energy.

Dark energy has the opposite
effect of dark matter.

Instead of binding galaxies
together, it pushes them apart.

The dark energy,

which we've only discovered
in the last decade,

which is the dominant stuff
in the universe,

is far more mysterious.

We don't have the slightest idea
why it's there.

What it's made from,
we don't really know.

We know it's there,
but we don't really know

what it is or what it's doing.

Dark energy is really weird.

It's as if
space has little springs in it

which are causing things
to repel each other

and push them apart.

Far in the future,

scientists think
that dark energy will win

the cosmic battle
with dark matter.

And that victory will start
to drive galaxies apart.

Dark energy's
gonna kill galaxies off.

It's gonna do that by causing
all the galaxies to recede

further and further away from us
until they're invisible,

until they're moving
away from us

faster than the speed of light.

So, the rest of the universe
will literally disappear

before our very eyes.

Not today, not tomorrow,
but in perhaps a trillion years,

the rest of the universe
will have disappeared.

Galaxies will become
lonely outposts in deep space.

But that's not going to happen
for a very, very long time.

For now,
the universe is thriving

and galaxies are creating
the right conditions

for life to exist.

Without galaxies,
I wouldn't be here.

You wouldn't be here.

Perhaps life itself
wouldn't be here.

We're lucky.

Life has only evolved on Earth

because our tiny solar system
was born

in the right part of the galaxy.

If we were
any closer to the center,

well, we wouldn't be here.

At the center of a galaxy,

life can be extremely violent.

And, in fact,
if our solar system were closer

to the center of our galaxy,

it would be so radioactive
that we couldn't exist at all.

Too far away from
the center would be just as bad.

Out there,
there aren't as many stars.

We might not exist at all.

So, in some sense, we are in the
Goldilocks Zone of the galaxy...

not too close, not too far,
but just right.

Scientists believe

that this galactic
Goldilocks Zone

might contain millions of stars,

so there may be other solar
systems that can support life

right here in our own galaxy.

And if our galaxy
has a habitable zone,

then other galaxies could, too.

The universe is immense,

and the amazing thing is that
we're always discovering more.

Every time we think we know
the answer to one problem,

we find it's embedded
in a much bigger problem.

And that's exciting.

There are
endless questions to ask

and mysteries to solve...

In our own galaxy,
the Milky Way,

and in galaxies
all across the universe.

10 years ago,
who would have thought

that we would be able
to identify

the black hole at the center?

Who would have thought
10 years ago

that the astronomical community

would believe in dark matter
and dark energy?

More and more,

scientific research
is focusing on galaxies.

They hold the key
to how the universe works.

We should be amazed
to live at this time, here,

at a random time
in the history of the universe,

on a random planet, at the
outskirts of a random galaxy,

where we can ask questions
and understand things

from the beginning
of the universe to the end.

We should celebrate
our brief moment in the sun.

Galaxies are born...

They evolve...

They collide...

And they die.

Galaxies are the superstars
of the scientific world.

And even the scientists who
study them have their favorites.

The Whirlpool galaxy, or M51.

I kind of like
the Sombrero galaxy,

if I had to put one on a wall.

The Sombrero galaxy,
ring galaxies...

they're just beautiful
to look at.

My favorite galaxy
is the Milky Way galaxy.

It's my true home.

We're lucky that the Milky Way

provides the right conditions
for us to live.

Our destiny is linked to
our galaxy and to all galaxies.

They made us, they shape us,

and our future
is in their hands.

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