Original subtitles

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.