All language subtitles for Spaces Deepest Secrets Killing the Milky Way 1080p

Narrator:
Our milky way is under threat.

Across the universe,
galaxies are going dark,

And scientists
are trying to find out why.

Something is slowly drawing the
curtains closed on the universe.

Narrator: Why are the stars in
our galaxy losing their shine?

Will the milky way
slowly fade to black?

If our home galaxy
is getting dimmer,

What does it mean for us?

Narrator: Astronomers are now
racing to unlock the mystery

Of why galaxies are darkening.

Is there a link to massive
bubbles of dust and gas,

That shoot out from the center
of the milky way?

We have discovered something
truly extraordinary.

Can the biggest collisions
in the universe

Switch the lights back on?

Oluseyi:
We thought galaxy collisions

Would be very violent
and destructive,

But what we find is that
they're one of

The most creative processes
in the universe.

Narrator: Scientists
are gathering evidence

For a startling theory...

Of how galaxies are born...

Live...

And die.

-- Captions by vitac --
www.Vitac.Com

Captions paid for by
discovery communications

♪♪

Our galaxy, the milky way,

Is just one of many
hundreds of billions of galaxies

In the universe.

Galaxies are huge,
glowing concentrations

Of gas, dust, stars,
and planets.

Telescopes capture
breathtaking pictures

Of bright, shining galaxies
millions of light years away.

Thaller: There are few things
that make my jaw drop

Like images of galaxies --

When you think about how vast
they are and just how beautiful

And also just how recent it is

That we understand
what these things really are.

The basic component that we see
of galaxies are stars,

And that's what keeps
these galaxies shining.

The milky way is
an enormous disc galaxy,

About 120,000 light years
across,

And it has several
hundred billion stars in it.

Narrator: In 2015, astronomers
make a worrying discovery.

They report that something
strange is happening

Across the universe.

Hundreds of thousands of
galaxies are getting dimmer.

Some have lost 50 percent
of their brightness

Over the past two billion years,

And the milky way
is one of them.

Tremblay: This isn't just
happening somewhere

In the deep void of space
in an unknown galaxy.

This is our home galaxy,

And anything that affects
our home galaxy affects us.

Narrator:
The way the galaxies recycle

Their precious star-building
material

Should keep them
shining brightly.

As some stars reach the end
of their lives,

They go supernova.

This giant explosion

Catapults a huge wave of gas
across the galaxy.

This wave injects new material
into interstellar gas clouds

And compresses them to the point
where gravity takes hold.

Gravity pulls the material
tighter together

And triggers the formation
of a new generation of stars.

Over time, this process
keeps the milky way bright

As billions of stars
burst into life.

♪♪

Thaller: To me, one of the most
beautiful stories ever told

Is the cycle of star formation.

So in a galaxy, you have these
giant clouds of dust and gas

That collapse
into massive stars.

Those stars then live
their lives and blow up

And distribute their material
back into the galaxy

For new stars and new planets
to be made of.

So that cycle of star formation
is what keeps galaxies bright.

♪♪

Narrator: But it appears that
something is going wrong

With this galactic circle
of life across the universe.

The shocking thing is that our
own galaxy could be in decline,

So the lights could go out
in our night sky.

Galaxies are huge systems of gas
and dust and stars.

So whatever's turning them off
must be something major.

Narrator: Why are galaxies
losing their shine?

And what does this process,
called galactic dimming,

Mean for our own milky way?

Astronomers believe that
the heart of our own galaxy

Is a good place
to search for answers.

The center of the milky way

Contains the greatest
concentration of stars.

Focusing on this area
gives scientists

Studying galactic
dimming a huge sample size

Compared to smaller clusters
of stars

On the edges of the galaxy.

Thaller: If you want to study
the history

Of star formation
in the milky way,

Why not look towards
where there are most stars?

And that's the center
of the galaxy.

Narrator: But astronomers face
a big problem --

Seeing clearly this far
into space from earth.

Thick clouds of dust and gas
lie between us

And the center of the galaxy.

These clouds block the visible
light that our eyes see.

Infrared light passes
through this dense gas.

Astronomers use special infrared
detectors to study objects

That other types of telescopes
cannot see.

But the water molecules
in earth's atmosphere

Absorb almost all
of the infrared light

Before it reaches
the planet's surface.

This reduces the level of detail

That the telescopes
on the ground see,

Even telescopes on mountaintops

Higher than 16,000 feet
above sea level

Struggle for clear view.

To overcome the problem,

Nasa and the german
aerospace agency build this --

The stratospheric observatory
for infrared astronomy,

Or sofia for short.

Sofia is a modified boeing 747

That flies in the stratosphere
above the clouds

And carries a high-powered
telescope.

With its eight-foot mirror
and infrared sensor,

The telescope sees
past galactic gas and dust

To detect objects
far out in space.

Sofia looks through a corridor
650 light years wide,

Right into the super
bright center of the milky way.

This has the most star-forming
matter in the galaxy,

So sofia's infrared sensors

Can count the number
of newly born stars.

The data from sofia,
combined with the data

From space telescopes
in orbit around the earth,

Builds up a super detailed image
of the center of the milky way,

Sofia's observations confirm

That the galactic center
contains the largest

And densest concentrations
of gas in the galaxy,

These dense gas concentrations
should collapse

To make new stars.

The more gas that collapses,

The more stars
that a galaxy creates.

But the telescope data shows

That this isn't what is
happening in the milky way.

Thaller: As we look into
the center of the galaxy,

We see these dense, dark regions
that should be forming stars.

But for some reason,
they're not.

Something is damping
down star formation

In the heart of the milky way.

Narrator:
The gasses left over from the
death of one generation of stars

Should help give birth
to the next generation.

But sofia discovers that many
of the giant gas clouds

In the center of the milky way

Are not collapsing
into new stars.

Astronomers find that these
gas clouds are giving birth

To ten times
fewer stars than expected.

Tremblay:
Though there are some regions

That are very dense with gas
and forming stars very actively,

Some places in our galaxy
still host gas,

And yet they're not
forming stars at all.

Without the light
from these new stars,

The galaxy
is losing its brightness.

Oluseyi:
Stars are temporary things.

They're born, and they die,

So in order for a galaxy
to stay the same brightness,

You need to have
a relative equilibrium

With the number of stars
being born

And a number of stars
dying equaling

So that the lights
don't really change.

And we had an image
of the milky way

From a few billion years ago,
what we notice

Is that the cumulative
amount of starlight has dropped.

Narrator:
The evidence is clear.

The milky way produces
fewer stars

Now than it did in the past,

And that is why it is dimming.

Fewer new stars means
that our galaxy is slowly dying.

What is putting the brakes
on star formation in galaxies

Like the milky way?

Are mysterious
galactic bubbles,

The key to solving
what is killing our galaxy.

Narrator: Galaxies across
the universe are getting dimmer.

Telescope observations
reveal that something

Is preventing the formation
of new stars in the milky way.

Thaller: Star formation
is a powerful process.

The scales are unbelievable,
and yet all over the galaxy,

Things seem to be shutting down.

Did something happen
in the past --

Something huge, some cataclysm

That actually shut off
star formation?

And can we find
any evidence of this?

Narrator: That evidence
could lie in data

From nasa's fermi telescope.

Fermi scans space for super high
energy light called gamma rays.

Tremblay: The gamma ray sky
is a completely different view

Of the universe.

The fermi telescope
is able to witness

The most energetic events that
are happening throughout it.

Narrator:
The telescope discovers
something incredible...

Two super huge bubbles
of gamma radiation

Emanating from the center
of our galaxy.

The bubbles extend
25,000 light years above

And below the spiral
of the milky way.

Plait: The scale of these
fermi bubbles is enormous.

They're roughly the radius
of the galaxy --

Half the width of the galaxy.

If you were to go outside
and look up in the sky,

They would cover 2/3
of the size of the sky.

Narrator: Only the most violent
events in the universe

Have the power
to produce gamma rays...

Like supernova explosions...

And neutron star quakes.

Neither is powerful enough

To unleash
the amount of gamma radiation

That turns into
the fermi bubbles.

So what made them?

Scientists think
an invisible monster

At the center of the milky way
could be responsible.

At the heart of every galaxy

Lurks a supermassive
black hole...

A point in space so dense that
nothing can escape its gravity.

Oluseyi:
From what we've observed,

Every galaxy has a supermassive
black hole at its core,

And there are at least
two trillion galaxies

In the observable universe,
so this means

There are trillions
of supermassive black holes.

Narrator:
The supermassive black hole
at the center of the milky way

Is called sagittarius a-star.

It weighs the equivalent
of four million suns.

This black hole's
enormous gravity

Draws in anything
that gets too close.

The energy unleashed when this
gravity rips apart stray stars

Could unlock the mystery of
what makes the fermi bubbles.

Black holes don't eat like
a nice, distinguished,

Gentrified person.

You know, they're sloppy.
They're like the cookie monster.

When the cookie monster
eats cookies,

More comes out
than goes into his mouth.

Well, supermassive black holes
are just like that.

Stuff is moving incredibly fast,
approaching the speed of light,

And the density and pressures
are incredible.

And so it's almost as if
there are explosions

In this traffic jam of material

Trying to get
into the black hole.

And so a lot of material
gets shot out

Away from the black hole
rather than ending up inside it.

Narrator:
The more massive the objects
that the black hole consumes,

The higher the densities
and pressures

Around the black hole become.

And the greater
the amount of energy

That blasts into space
as gamma radiation.

Scientists rewind the
milky way's galactic clock.

They predict when
sagittarius a-star feasts

On a meal large enough
to forge the fermi bubbles.

Some scientists estimate that
around three million years ago,

Sagittarius a-star draws
in a vast amount of matter.

That flattens out into
a huge, glowing, spinning disk.

As the black hole
devours this matter.

Two immense jets of energy
blast out from its poles.

These jets blast gas
out of the galaxy

25,000 light years into space.

The jets turn off when the
black hole finishes its feast.

All that remains are
the fermi bubbles we see today.

Scientists think that multiple
events like this one

Throughout the history
of the milky way

Could unlock the mystery
of, "why are galaxies dimming?"

The reason lies in the huge
amount of heat they unleash.

Stars form when huge quantities
of gas and dust collapse

Under gravity.

The process triggers
a nuclear reaction.

Scientists calculate
that this reaction

Happens only
when the gas is cold.

Plait:
Star formation is a battle

Between these two forces
of gravity,

Which is trying to collapse
the cloud,

And its own internal heat,
which is trying to inflate it.

For gravity to win,
for stars to get made,

The gas has to be cool enough
that it doesn't stay inflated,

That it's able to collapse.

Narrator: The jets that
sagittarius a-star releases

Hurl some of the richest
star-building material

Into intergalactic space.

This superheats the gas
at the center of the milky way.

The clouds of gas become
too hot to collapse into stars.

Oluseyi: All of this heat
and power and light and force

Would have stripped out
all this material

From the center of the galaxy.

So it just would not have been
available to form new stars.

Narrator:
A series of events like these

Happening at different times
in our galaxy's history

Could put the brakes
on star formation

At the heart of the milky way.

Telescopes look millions
of light years

Through space at other galaxies.

They discover that the damage
sagittarius a-star wreaks

On the milky way
throughout its past

Is not unique.

Astronomers observe
2,000 galaxies

That show evidence of huge blast
of gamma radiation

Coming from the black holes
at their centers.

And the vast majority of these
galaxies are now getting dimmer.

Tremblay: We see it in an
enormous number of galaxies

Throughout the universe --

Direct signatures of violent
black hole activity

And a depressed
star formation rate.

There's definitely
a clear connection.

Narrator:
But do bursts of radiation
from a supermassive black hole

Spell doom
for a galaxy indefinitely?

And do mysterious alien stars
unlock

How it might be possible
to reverse galactic dimming?

Narrator: Jets that blast out
from supermassive black holes

Kill star birth
at the center of galaxies.

They could explain why
our milky way is dimming.

Will the curtains close
on our galaxy forever,

Or is there a way it can get
a new lease of life?

Scientists believe a clue
could lie inside a space rock

That fell to earth.

In 1969, a meteorite lands

Near to the small town
of murchison, australia,

One hundred miles
north of melbourne.

It shatters into pieces, and
locals gather over 100 kilograms

Of the black,
smelly meteorite fragments.

In 2019,
scientists grind down a sample

To analyze what it is made of.

They get a big surprise.

They find grains of dust
from alien stars that died

4.6 billion years ago,
before our sun was even born.

These grains of stardust become
locked inside space rocks

Through the stars'
never ending cycle of birth

And rebirth.

Billions of years ago,
an ancient star in the milky way

Reaches the end of its life.

Chemical reactions inside
the star makes it grow rapidly.

It transforms into a red giant.

The outer layers of the star
shed grains of stardust.

These grains travel light years
through space

And merge with the spinning disc
of gas and dust

Surrounding newly formed stars.

The stardust from the dead
red giant

Combines with the material
in the disk to make asteroids.

It is a part of just
such an asteroid

That falls on murchison
as a meteorite in 1969.

These grains of dead stars
might reveal if galactic dimming

Caused by blast of gamma
radiation spells doom

For galaxies like the milky way.

Different types of grains
come from different dead stars.

Adding up the unique grains
tells astronomers

How many stars existed
in the milky way

At certain times in the past.

These little pieces of stardust
inside this meteorite tell us

The story of what was happening
in our galaxy

Before our sun even formed.

They're little tracers.

Narrator:
The stars that eject the grains
found in the murchison meteorite

Lived for between two
to 2.5 billion years.

So it is possible for scientists
to calculate

When these
ancient stars were born.

By knowing that these grains
came from dying stars,

We can actually trace backwards
in time

To when those dying stars
were actually first forming.

Narrator: Scientists discover
that these grains

Come from different stars
from all over the galaxy,

But they share one thing
in common.

They are all born
seven billion years ago.

Calculations reveal
that the rate of star birth

In the milky way at that time
is double the average.

Tremblay: This was a beautiful
and exciting result.

It showed that the milky way
experienced

What might have been a sudden

And unexpected burst
of star formation

About seven billion years ago,

And this might not
have been a localized event.

It might have been galaxy wide.

Narrator:
These grains show that galactic
dimming is not inevitable.

Galaxies like the milky way

Experience periods
of intense star building.

These events,
counter galactic dimming.

They make galaxies
much brighter.

Thaller: A galaxy is such a rich
and complex thing,

It turns out that its life cycle
is not very simple.

They grow, they change,
they evolve,

And in fact, their story
may not be so doomed after all.

Narrator: What triggers these
sudden bursts of star creation

Within galaxies
like the milky way?

♪♪

A clue lies in the findings
from an observatory

In new mexico.

This is the sloan 100-inch
telescope.

Sloan's apogee project studies
hundreds of stars

In the milky way simultaneously

During a single observation
session.

One of the most powerful things
that we can do as astronomers

Is take a survey
of the night sky,

Of looking at huge chunks
of the sky at the same time,

And mapping out
all of the stars there.

Narrator: The light from a star
reveals information

About the chemicals it contains.

Apogee analyzes this starlight

To unlock the precise chemical
makeup of thousands of stars.

So you take the light that any
particular star emits,

You break it up into a rainbow,
and you can see the fingerprints

Of all the different chemicals
in there, the ratios of them,

How much there is of
one thing versus another.

Every single chemical
has its own rainbow fingerprint.

Narrator: The results from
sloan's apogee project reveal

That there's something
very strange about the chemicals

Inside some of the stars
in the milky way.

Stars contain 98 percent
hydrogen and helium.

And traces of other elements
like iron, magnesium, or carbon.

Apogee analyzes the light
from over 600,000 stars

To decode the chemical
signature of each one.

It finds that nearly all stars
in our galaxy,

Regardless of their size
or color,

Share a common signature.

But every now and again,
apogee finds a rogue star...

With a different signature.

How is this possible?

Astronomers studying
these odd stars out

Come to an astonishing
conclusion.

Oluseyi:
Their ratios don't match

Everything else
in the milky way.

By identifying stars that have
a different chemical signature

Than other stars
in the milky way,

The implication is clear --

These stars did not originate
in the milky way galaxy.

Narrator: If these stars weren't
born in the milky way,

Then where do they come from?

And do they unlock how to
reverse galactic dimming?

Narrator: Astronomers discover
that our milky way

Contains mysterious alien stars

That were not born
in our galaxy.

So where do they come from?

And what is their connection
to galactic dimming?

The european space agency's
gaia telescope finds a clue.

The telescope maps the motion
of over a billion stars

In the milky way.

It discovers that these
odd stars out all travel

On different orbits to stars

That share the typical chemical
profiles for the milky way.

They circle the galactic center

In the opposite direction
to other stars

And move on elongated
oval-shaped orbits.

The results from gaia
lead to a startling conclusion.

These alien stars
come from a different galaxy.

But how can a star
jump between galaxies?

A clue lies 250 million
light years from earth.

This is a galaxy named arp 220.

It has one of the strangest
shapes of any known galaxy

In the visible universe.

Arp 220 does not look like
a regular calm, beautiful,

Majestic spiral galaxy
like the milky way.

It is this train wreck blob.
It's an absolute mess.

Narrator: Why does arp 220 look
so different to other galaxies?

The answer is arp 220
isn't a single galaxy.

Oluseyi:
The bent shape of arp 220

Isn't just because
of aesthetic reasons.

It tells us something
about the galaxy's history.

It appears to be the result of
a merger between two galaxies.

Narrator: The merger of two
galaxies after a collision

Explains how alien stars can
jump from one galaxy to another.

The discovery of odd stars out
in the milky way

Is evidence that our galaxy,
too,

Is involved in a collision
billions of years ago.

Now we understand
that galactic collisions

Are responsible
for these odd stars in the sky.

They didn't come from
the milky way galaxy.

So it's an amazing thing
to think

That when you look up
in the sky,

Some of even the nearest stars
may have began their lives

In an entirely different galaxy.

Narrator: Astronomers believe
that these galactic mergers

Unlock what triggers intense
periods of star birth

In galaxies like our own.

The clue is that merged galaxies
like arp 220

Are some of the most brilliant
objects in the universe.

There are some galaxies
in the universe

That are putting
on a spectacular show.

They're incredibly bright.

Their name says it all -- ultra
luminous starburst galaxies.

Narrator: The brightness
of a galaxy like arp 220

Is a telltale sign

That it is producing
huge numbers of new stars.

The raw ingredients
for this starburst

Are the vast clouds of gas

That wrap themselves
around every galaxy.

Oluseyi:
When two things merge together,

There's a lot of reproduction
of stars.

New stars are being born.

Just like we had a baby boom,
we have a star boom.

Narrator:
700 million years ago.

Two enormous spiral galaxies
are on a collision course.

Stripping away their stars
and planets

Reveals what happens
when they collide.

The galactic gas and dust
compress in the collision.

This triggers the formation
of billions of stars.

Over millions of years
and multiple collisions,

The two galaxies merge
into a new galaxy

That is incredibly bright --

Arp 220.

So a galaxy collision sounds

Like a really violent event,
right?

But in fact,
it can seed new life.

Gas is the fuel from which
all stars are born.

So when you introduce new gas
to emerging galaxy,

You can form
a new generation of stars.

Narrator: Observations reveal
arp 220's origin is not unique.

Astronomers believe
up to 80 percent

Of ultra luminous
starburst galaxies

Are the result
of galactic collisions.

Could a cosmic merger be
responsible for the epic periods

Of intense star building
and the milky way's past?

And when will the milky way's

Next galactic mega collision
take place?

♪♪

♪♪

Narrator: Scientists are
on a mission to discover

How galaxies can reverse
the effects of galactic dimming.

The brightest galaxies
in the universe reveal

That the galactic collisions
breathe new life into a galaxy.

So when was the milky way's
last major collision?

Astronomers plot the positions
and movements

Of both the old
and new stars in our galaxy.

They use this data
to rewind time

And reveal
the event that triggers

One of the greatest-ever periods
of star building

In the milky way.

Around 10 billion years ago,
the milky way collides

With a smaller, ancient galaxy
called gaia-enceladus.

The impact compresses together
huge clouds of gas.

This gas collapses to make
thousands of brand-new stars.

The milky way brightens
as more and more stars form.

The past collision of the milky
way with gaia-enceladus

Might have introduced
an enormous new reservoir of gas

Into our home galaxy,
and that gas could have gone

Into forming
a new generation of stars.

Thaller:
When you think galaxy collision,

It sounds like
something destructive.

But in fact, when one galaxy
collides with another,

That's a harbinger
of the creation

Of a brand-new generation
of stars.

Our own sun may have formed
when a small galaxy

Collided with the milky way
billions of years ago.

It's an act of violent creation.

Narrator: A mega collision
10 billion years ago

Reversed the milky way's
galactic dimming.

Where else has the gas needed

To make new stars
come from since then?

In 2020, astronomers using data
from the gaia space probe

Uncover a clue.

Gaia spots a cluster of a few
thousand bright young blue stars

In an ancient outer region
of the milky way.

These stars burst into life

Along a stream
of fresh hydrogen gas.

Gaia follows the gas trail
into intergalactic space

To a cluster of stars
outside the milky way.

Our galaxy
is not alone in space,

The milky way is surrounded
by dozens of smaller galaxies.

And where we have maybe
a hundred

Or a few hundred billion stars,

These galaxies
only have about a billion.

It's like we're a whale
in the ocean

Surrounded by a school
of little fish.

Narrator:
The new star-building gas

Comes from the largest
of these dwarf galaxies,

Called the large
magellanic cloud.

The huge gravity
of the larger milky way

Continually strips gas
from the smaller dwarf galaxy.

The new gas collides with
the outer regions of our galaxy.

Thousands of bright, young
blue stars burst into light.

Astronomers estimate
that the milky way

Will completely tear apart
the cloud

Within the next two and a half
billion years.

♪♪

Dwarf galaxies like the large
magellanic cloud

Keep the milky way
topped with star-building gas.

Oluseyi:
The milky way isn't isolated.

It has a lot of neighbors,

And it's stealing gas
from some of them.

It's ripping them apart

And incorporating that material
into itself.

And that's the material that may
form new stars of the future.

The milky way is literally
sucking the gas

Off of its neighbors
to keep itself alive.

Narrator: Astronomers think that
there is enough gas

In these satellite galaxies

To keep the milky way fed
for a few billion years.

But where will the critical
supplies of gas come from

Once these smaller galaxies
are exhausted?

Thaller: We want to know
what's going to happen to us,

To our star,
in the very distant future,

And knowing the future
of the milky way

Will help us understand what's
gonna happen to our home.

Narrator: Astronomers scan
the cosmos to identify

Where the milky way's
next meal will come from.

They discover that it is
our own galaxy

That might be next on the menu.

The milky way has
fed off the gas

From around 50 smaller satellite
galaxies for billions of years,

But it might be about
to meet its match.

Nearby on a cosmic scale
is andromeda

And its satellite galaxies.

Andromeda has over
800 billion stars,

More than double the number
in the milky way.

This juggernaut
is hurtling towards us.

The stage is set
for a mighty cosmic showdown.

When will this clash
of the galactic titans happen?

And what will it do
to the milky way?

♪♪

♪♪

Narrator: Astronomers believe
the milky way is destined

To collide with our galactic
neighbor, andromeda.

They race to discover
when this mighty cosmic faceoff

Will take place.

Tremblay:
The milky way and andromeda

Are two of the most massive
galaxies in our local group,

And we know that they're
moving toward one another

And will eventually collide.

So what we want to discover now

Is whether they're on
a direct collision course

And they're headed
right for one another

Or whether they're gonna
continue to dance

Around each other
for several billion more years.

Tremblay: Telescopes from around
the world scan andromeda

To unlock its speed
and trajectory.

They discover that andromeda
and the milky way

Will smash into one another

Within the next
five billion years.

The result will be a period
of star creation

Unmatched in the history
of our galaxy.

Oluseyi: We now have the most
accurate prediction

Of when this collision
is gonna take place,

And when it does, it's gonna
set the skies alight

Because there's gonna be
a huge burst of star formation.

Narrator: The massive sizes of
the milky way and andromeda

Give them huge gravity.

The two galaxies speed
towards each other

At over 250,000 miles per hour.

Their gas reserves smash
together when they meet.

This triggers a super intense
period of star creation.

Billions of new stars
burst into life.

The spiral arms of the milky way
and andromeda tangle together.

They eventually form a giant
super galaxy called milkomeda.

What a sight that will be.

I mean, it's beautiful enough
going out now

And seeing our galaxy as it is,

But we're adding a whole
other galaxy to our own.

There will be more stars,
more gas out there,

More things to see,
more structures in the sky.

It will be fantastic.

Narrator: Today, a drop off
in star formation

At the center of the milky way

Means our galaxy
is losing its shine.

The creation of milkomeda

Will throw this galactic
dimming into reverse.

This new galaxy will make
billions of bright, new stars

In the space of
a few hundred million years.

But scientists believe
that our galaxy will then move

Into the final stage of its life
after this dramatic merger.

The light
from a billion new stars

Bursting into life so quickly

Blasts away surplus gas.

This prevents the birth
of new stars in the future.

Oluseyi:
The formation of bright stars

Is gonna drive out gas and dust,

And then when the big stars
start exploding,

That's gonna drive out
even more.

So this birth may just lead
to the end of star formation

In the galaxy.

Tremblay: We think of galaxies
as these immortal structures,

These vast swirling voids
of hundreds of billions of stars

That live for all of time,
but in fact, it's not true.

Galaxies change and evolve
and eventually die.

Narrator: Milkomeda will inhabit
a sparsely populated part

Of the universe.

There will be no nearby galaxies
to feed from

To rejuvenate
the lost gas supply.

Oluseyi: Once the milky way
and andromeda merge

And form a new, larger galaxy,

It has this huge burst
of star formation.

After that, things are gonna go
a lot quieter

Because we're relatively
isolated right now.

It's just the two of us.

Narrator: Milkomeda is condemned
to terminal decline

And extinction.

After the giant galactic
fireworks show

That will be the collision
of the milky way and andromeda,

We're live
in this simmering ember

That will continue to cool off
for billions of years more.

Ultimately, our existence
as a civilization is nothing

But a sentence
in the book of the universe.

Narrator:
Astronomers are now unlocking
the life story of our milky way.

Mega bubbles of gas

Reveal how supermassive
black holes generate heat

That stops star birth
and makes galaxies grow dim.

Weird alien stars show
how galactic collisions

Rejuvenate galaxies
and make them grow bright again.

Today, the milky way is passing
through a phase of dimming.

But the light show we see
from earth is still spectacular.

Thaller: I want you to realize
that we live

In this tremendously
fortunate time.

Go outside
and look at the stars.

Feel this joy seep through you.

You are standing
in this wondrous moment.

Enjoy it and celebrate it.

Narrator:
The milky way will enter
a new stage of its evolution

And five billion years' time --

One final cosmic blowout.

Before it slowly fades away
into the darkness.