MIKE ROWE: Our universe is at war.
The universe is a very violent and deadly place.
ROWE: Entire galaxies fight to the death.
OLUSEYI: Talk about clash of the Titans.
It doesn't get more titanic than this.
It's a slaughter. It's a massacre.
ROWE: Only the strongest survive.
If a galaxy wants to stay alive,
it has to feed on other galaxies.
ROWE: Our own galaxy also fights for survival.
We are facing the ultimate destruction
of the Milky Way Galaxy.
ROWE: These battles are how galaxies live,
grow, and die.
These collisions got us to where we are today,
and they're going to determine the future of the universe.
♪♪
In 2018, astronomers used the Gaia
space telescope to map our Milky Way Galaxy.
They tracked the movements of a billion stars,
and they found that some behave very strangely.
When astronomers were mapping stars in our galaxy,
they found a whole bunch that we're on similar
but very strange orbits.
Most stars of the Milky Way are orbiting in a sort of
regular pattern, but these stars
at the center, they're in these highly elongated orbits.
Coming in from very far,
swinging around the center of our galaxy, and then going back
out again, a little bit like a comet does.
ROWE: This group of stars plunges
wildly through the center of our galaxy.
When you track their direction and speed on a chart,
you get a shape that looks a bit like a sausage.
This doesn't sound very science-y,
but this sausage is really what the stars look like
if you look at the shapes
of their orbits in a certain configuration.
ROWE: What sent so many stars on such a strange path?
It must have been a huge event.
We think these stars are the result of a past
cosmic collision.
ROWE: They are casualties from an enormous battle between
the Milky Way and a foreign galactic army.
BULLOCK: They don't move like stars in the Milky Way,
because they're not from the Milky Way.
These stars are actually alien stars.
They're invaders from outer, outer space.
ROWE: The attackers left their mark on the Milky Way.
We find similar battle scars on galaxies across
the universe.
Our models of galaxy information are still
pretty uncertain.
We still don't really understand how galaxies got to
where they are, how we go from the Big Bang to the Milky Way.
ROWE: Wars between galaxies have profound consequences, for
the winners, the losers, and for us.
What we're learning is that these galactic battles have had
a huge impact on what the universe looks like today.
THALLER: Our understanding of galaxies has changed
entirely in the last few decades.
We understand now that every big galaxy like the Milky Way
started from many smaller things colliding,
changing each other as they went.
ROWE: Nearly 10 billion years ago,
the sausage stars were part of a foreign galaxy.
It was on a collision course with our home, the Milky Way.
We call this invading army the Sausage Galaxy,
or Gaia-Enceladus.
PLAIT: The galaxy that we fought probably had
about 50 billion stars,
so we're talking about something that is a significant
fraction of the size of the Milky Way.
ROWE: Gaia-Enceladus was a tough opponent,
but the Milky Way was 20 times its mass,
and that makes a huge difference.
When galaxies interact with each other,
size definitely matters.
The bigger galaxies are gonna dominate over the smaller ones,
ripping them apart and essentially consuming them.
Galaxy interactions are all about bullies.
The bigger you are, the badder you are.
SUTTER: When two galaxies collide,
it's like two massive armies marching towards each other.
These galaxies aren't fighting
with knives or spears or guns or even nuclear bombs.
They're fighting with something
much more powerful -- Gravity itself.
ROWE: Each galaxy contains billions of stars and planets
and a supermassive black hole,
millions of times the mass of the sun.
That's a lot of gravitational firepower.
SUTTER: As these galaxies approach each other,
you can get tidal effects -- The same way that the moon can
raise tides on one side of the Earth and the opposite side,
one galaxy can stretch another
galaxy along a certain direction.
ROWE: As Gaia-Enceladus advanced towards us,
our galaxy's superior gravity grabbed
hold of the smaller galaxy.
As it approached, the gravity from the Milky Way
would have stretched it out.
ROWE: Gaia-Enceladus was distorted but not defeated.
The battle was just beginning.
It would have passed through our galaxy,
maybe orbiting a couple of times before being torn
apart by our gravity.
ROWE: The Milky Way's gravitational power
ripped Gaia-Enceladus apart
and captured billions of its stars.
Eventually, most of those stars would have
then settled down into
the disk of the Milky Way and become a part of it.
Little galaxy try to take on the Milky Way --
You're gonna get what's coming to you.
ROWE: Despite winning the battle,
the Milky Way suffered serious damage.
The collision with the Sausage Galaxy
left a scar on the Milky Way.
And when we look near the center of our galaxy,
we see a bulge that's left over from that collision.
ROWE: The Milky Way isn't the only galaxy scarred by war.
Across the universe,
rival armies made up of billions of stars slug it out,
leaving behind distorted and damaged casualties of war.
HOPKINS: There's a million different
sub-categories of them.
There's tadpole galaxies that have long tails,
longer than our own galaxy.
There are things like Arp-Madore 2026, where you see
this eerie, glowing face,
two big eyes looking right at you from across the universe.
There are galaxies that looked like they might have collided
with one another and blown holes through each other.
ROWE: These battle scars give us important clues
about one of the biggest mysteries in astronomy --
How galaxies develop and grow.
But there's a problem.
We can't watch these battles in real time.
The scale of galaxies is huge.
They're hundreds of thousands of light years across.
It's going to take them millions
or billions of years to come together.
So it's like looking at one frame
from a really energetic fight scene in a movie.
ROWE: By piecing these snapshots together,
astronomers can build up a detailed picture of past
conflicts and discover how these battles transformed
galaxies over billions of years.
We have pictures of isolated galaxies,
we have pictures of interacting galaxies,
and we have pictures of aftermath galaxies.
ROWE: And that's helped us discover something alarming.
The Milky Way faces yet another attack from
an enemy armed with an enormous secret weapon.
Will our solar system survive the onslaught?
ROWE: Across the universe,
galaxies are at war,
Their main weapon --
Gravity.
It tears the combatants into weird and wonderful shapes.
Our galaxy didn't escape the mayhem.
It's peppered with battle scars.
The overall shape of the Milky Way
is a flat disk of stars and gas.
Except recently, we have found out that at the edges,
it's actually warped a little bit like the brim of a fedora.
The stars actually dip down below the plane on
one side and dip above it on the other.
ROWE: We think the attacker was one of our satellites,
a galaxy that orbits the Milky Way like the moon
orbits the Earth.
It's called the Sagittarius Dwarf Galaxy.
From looking at how the stars move in the Milky Way,
we suspect that the Sagittarius Dwarf Galaxy has
actually crashed through the Milky Way a few times on
its course of its orbit around the galaxy.
BULLOCK: It came in about six billion years ago,
hit the disk hard about two billion years ago, and crashed
again about a billion years ago.
PLAIT: And our gravity has pulled it out into a gigantic,
looping stream of stars that is moving in and out
of our Milky Way.
ROWE: The war is not over.
The insurgent galaxy will return.
When galaxies interact,
often they're caught in this huge cosmic dance
where they revolve around each other a few times,
or they even crash through each other and then come
back around.
The Sagittarius Dwarf Galaxy looks like
it's crashing in with ever increasing frequency.
ROWE: A new skirmish could take place in the next
100 million years.
So should we be worried about these attacks?
SUTTER: Because the Sagittarius Dwarf Galaxy is so small
compared to the Milky Way,
it will do some damage at the beginning,
but because we're so massive, we can absorb the impact.
I mean, this galaxy, it's looking for a fight,
but it's also 10,000 times smaller than us.
So this is gonna be no sweat at all.
ROWE: So far, the Milky Way has been victorious.
But the danger isn't over.
We are surrounded by enemies.
SUTTER: Our local neighborhood of galaxies
has three major galaxies,
but up to 50 smaller ones.
All these galaxies are potential troublemakers.
Each one of these could be armies that rise up against us.
The two most famous galaxies that orbit
the Milky Way are the Large and Small Magellanic Clouds.
These are two independent dwarf galaxies that you can
see in the night sky from the Southern Hemisphere.
ROWE: We thought the Large Magellanic Cloud orbited
our galaxy at a safe distance of 160,000 light years.
We thought it would stay that way,
and we thought it was harmless.
Now, a new discovery shows we were wrong on all counts.
The new factor that changed our view of the Magellanic Cloud
is we found out
it has a lot more dark matter than we thought.
ROWE: Dark matter,
the most mysterious stuff in the universe.
A dark matter is literally what it sounds like.
It's matter that we cannot see.
But it has gravity and can affect objects
that we can see.
ROWE: Adding in this extra dark matter makes the Large
Magellanic Cloud at least twice a massive as predicted.
So its gravity is double what we thought.
It's secretly been gathering
allies, has been gathering dark matter on its side,
and now it's a much bigger threat than we thought before.
So it's not just going to orbit us.
It's gonna collide with the Milky Way.
ROWE: Moving at nearly a million miles an hour,
the Large Magellanic Cloud will not swing past us.
It will attack.
The large Magellanic Cloud is
1/10 the mass of the Milky Way.
That's enough to make a pretty big punch.
ROWE: In about 2.5 billion years,
it will smash into our galaxy.
SUTTER: It's gonna plow through the disk of the Milky Way,
it's gonna blow a cavity.
It might even damage our spiral arms.
ROWE: Earth sits in one of those spiral arms.
Could our planet become collateral damage?
If the Large Magellanic Cloud passes through the plane
of our galaxy near our location,
that can have dire consequences.
ROWE: The gravitational clash between
the invader on the Milky Way
could hurl stars and planets out of our galaxy.
Earth could be one of them.
HOPKINS: Our planet's very close to its own star,
so the odds are that you'll just get ripped out
along with your star,
so we'd be moving along with the sun even as the sun gets
jettisoned from our galaxy.
PLAIT: And it'll move off out into intergalactic space.
And that's not terrible.
I mean, it's not gonna get destroyed,
but it's a little lonely.
ROWE: Our view of the night sky
would radically change.
OLUSEYI: We'd be able to see much more of the Milky Way,
especially if we got kicked up above the plane of the galaxy.
We'd be able to see the whole shebang.
Just look at any image of a spiral galaxy.
They're gorgeous. Now imagine seeing your night
sky filled with a face-on spiral galaxy.
[scoffs] That would be like waking up to my face
every morning -- spectacular.
[laughs]
ROWE: If we were unlucky,
our home planet could have
a close encounter with an invading star.
PLAIT: The odds are very low that another star
will pass close by the sun,
but those odds aren't zero.
It could happen that another star
passes close enough to affect the planets.
And if that were to happen,
it could upset the delicate balance in the solar system.
OLUSEYI: We don't know where the Earth could end up.
It might find its way into the sun.
You just don't know.
Or there might just be a rain
of comets into our inner solar system.
MINGARELLI: Our own planet might be flung out,
in which case, this would be a death knell for all life
on Earth.
I'm not someone who is like a doom and gloom person,
but, like, that would be insane.
OLUSEYI: You don't know what's gonna happen,
but most of the options are bad.
ROWE: All these nightmare scenarios
will extinguish life.
Earth might survive, but our cosmic
zip code will take a severe beating.
SUTTER: The Milky Way Galaxy is bigger than
the Large Magellanic Cloud,
so we are gonna win, [exhales heavily]
but it's gonna hurt us for a long time.
ROWE: The Large Magellanic Cloud
will leave our galaxy battered,
bruised, but ultimately undefeated.
But there's a far bigger threat looming
over the Milky Way.
It's gonna face an opponent that it can't defeat.
ROWE: Will this mega collision be
the Milky Way's last stand?
ROWE: For billions of years,
the Milky Way conquered galaxy after galaxy,
tearing its smaller rivals to pieces.
But our galaxy is about to meet its match.
In the not-too-distant future, galactically speaking,
a much, much larger battle is due for the Milky Way.
ROWE: A battle with a local superpower,
the Andromeda Galaxy.
We thought this huge galaxy might wound us in the future.
Now, recent evidence reveals it's going to make
a full-scale assault.
We've known for a long time that Andromeda is heading
more or less toward us,
but we didn't know exactly in what direction.
But in recent years, we've been
able to pinpoint this a lot better.
And, uh, yeah, it's -- It's heading right for us.
ROWE: Data from the Hubble Space Telescope shows
two galaxies will collide in about four billion years,
and it will be a monumental battle.
This collision that is coming, and it is coming, is not gonna
be anything like the Milky Way has experienced before
in its 10- or 12-billion-year history.
This is a galaxy of comparable size.
This is two heavyweight prize fighters coming at it.
ROWE: Warriors with the same gravitational firepower.
Simulations suggest a clash of the Titans.
BASRI: Each of them with half a trillion stars in them.
That sounds like a pretty spectacular collision.
ROWE: Fights between equally matched galaxies
are rare and messy.
When the battle kicks off,
there will be no good news for either side.
PLAIT: When the Andromeda Galaxy and the Milky Way Galaxy
start to get close,
they're gonna start affecting each
other profoundly.
Tendrils of stars are gonna be thrown out.
Gas is gonna be thrown out.
ROWE: It won't be a single impact.
Gravity will send the two opponents
into a spiraling dance of death.
PLAIT: The first pass is actually not a direct hit.
They're gonna swing past each other, in fact.
And at this point, their gravitational
interaction is gonna slow them down,
and they're gonna come back toward each other.
ROWE: The galaxies will collide and fly apart again,
inflicting more and more damage with each clash.
If you were to go outside and look up,
you could see the disk of our galaxy getting ripped apart
by tidal interactions with Andromeda.
ROWE: The two beautiful spiral galaxies
will tear each other apart,
leaving one vast elliptical galaxy.
PLAIT: The fate of the Andromeda, Milky Way
battle is that they will merge.
This is going to be one gigantic galaxy.
OLUSEYI: And that presents a problem.
What are we gonna call this new galaxy?
Of course, my nerd colleagues have come up with
names like Milkomeda, Andromeway.
Whatever, those are corny.
We should just call it Hakeem.
ROWE: With a trillion stars, it will be
one of the biggest galaxies in the universe.
OLUSEYI: In the Hakeem Galaxy,
things gonna be completely new.
First off, it's gonna be a really good-looking galaxy.
Let's get that straight from the get-go.
Second, it's gonna be powerful, and I'm talking powerful.
This may be the most remarkable
galaxy in the history of the universe.
ROWE: Milkomeda, or Hakeem, if you prefer,
will become the undisputed boss of our cosmic neighborhood.
It's calm appearance concealing
a history of violence.
It's the result of a complete war zone of mergers over
the course of billions of years,
many galaxies crashing together, fully reconfiguring
each time and slowly, you grow
this smooth, placid, big blob of stars.
ROWE: After billions of years of warfare,
our galaxy will finally be peaceful.
But before it's honorable discharge, Milkomeda
may produce one final,
devastating act of war.
Imagine World War II, and then all of a sudden,
one of the sides comes up with the Death Star.
That's what we're talking about here.
ROWE: A weapon of cosmic destruction.
♪♪
ROWE: When giant galaxies clash,
the battles are spectacular and destructive.
The victors steal huge numbers of stars and vast amounts
of gas as fuel for the ultimate super weapon.
The special weapon that these monster galaxies
have is a giant Death Ray,
a jet of material racing across thousands of light-years.
ROWE: These huge outbursts of energy blast out
of the center of the colliding galaxies.
They produce more energy in one second than
the sun will in its entire 10-billion-year lifetime.
We call them jets.
These incredibly powerful jets aren't just brief features.
They can be sustained for millions of years,
and they can maintain their structure
for thousands of light-years.
It's like turning on a garden hose
in Chicago and using it to water
a garden in London.
ROWE: Exactly what triggered these jets was a mystery.
Then, in June 2018, astronomers in Hawaii captured
something stunning -- A jet forming
during a galactic collision.
The team found something really incredible.
They found two galaxies that were in a cosmic collision
and actually found an active jet in one of these galaxies.
It was the first time anything like this has been discovered.
ROWE: When galaxies collide, the clash drives huge clouds
of gas and dust towards their centers.
The supermassive black holes start to feed.
The gas that was in those galaxies starts to
funnel toward the black hole and then fall upon it.
ROWE: Not all this gas ends up inside
the supermassive black hole.
Powerful magnetic fields carry some of
this matter to the poles
and blast it out in tight, narrow jets.
A super weapon is born.
This discovery helps us understand
how giant elliptical galaxies form.
Knowing that mergers of spiral galaxies can cause
these jets helps us put together
a complete picture of how these huge elliptical
galaxies might be formed.
ROWE: The discovery doesn't answer all our questions.
There's another mystery.
How did the super giant galaxies that
dwarf the Milky Way get so big?
Our Milky Way Galaxy is big-ish.
It's -- it's slightly bigger than average,
but IC 1101, for example,
is more than 50 times larger than our home galaxy and has
more than a trillion, with a T, a trillion stars in it.
The biggest galaxies make the Milky Way look like an ant.
These galactic giants pose a problem.
There hasn't been enough time since the birth of
the universe for them to become so large,
even by conquering smaller galaxies.
When we look into the distant universe,
we see something very strange that we don't quite understand.
We see enormous galaxies that existed just
a billion years after the Big Bang.
And even though these cosmic collisions help explain how
galaxies get bigger,
they don't quite explain everything about how galaxies
grow over time.
So we still have a big mystery on our hands here.
ROWE: So in 2019, an international team
investigated a very large galaxy
over 300 million light-years away.
We call it NGC 6240.
MINGARELLI: NGC 6240 was being studied because
it had two supermassive black holes in it.
Now the galaxy itself looked like it
had been disturbed, like something had happened.
They thought that potentially it had had a recent merger.
ROWE: They were expecting to see two
supermassive black holes in the galaxy's heart.
As the researchers peered through the layers of gas
and dust, they discovered something surprising.
What we found was staggering.
We found not two but three
supermassive black holes lurking in the center.
ROWE: It's the first time we found
a galaxy with three supermassive black holes,
evidence of a three-galaxy pile up.
This galaxy is an active battlefield of
not two but three armies colliding at once,
and because there are three armies involved,
there are three galaxies involved with
three times as much mass, three times as many stars,
three times as much material, and three times as
much violence.
ROWE: This three-way battle may explain how
the largest galaxies got so big so fast.
MINGARELLI: It could be that galaxy mergers
are more frequent than what we thought previously,
and therefore, galaxies become more massive
faster than previously expected.
ROWE: In the past, galaxies may have
battled and collided more often than today.
Back then, galaxies were more densely packed together.
Our universe is expanding as it ages, which means in
the past, all the galaxies in
the universe were closer together,
and that means they had greater chance for their
gravitational interactions to
pull them together and smash them together.
ROWE: The early universe was at war.
Conflicts between galaxies were common.
They collided frequently and grew quickly.
But not every galaxy profited from the carnage.
Some brave galaxies took on the big guns
and nearly died as a result.
ROWE: When galaxies fight, the big get bigger.
More mass means more gravity, the vital ingredient
for victory.
But galactic conflict doesn't always result in growth.
A strange new astronomical object had
scientists confused.
MINGARELLI: They just looked like stars from the ground.
However, with the advent of Hubble and beautiful
space-based telescopes,
it was possible to look at these stars again and actually
discover that they were galaxies.
HOPKINS: They're kind of crazy.
They're a huge number of stars, but crammed into an incredibly
tiny space on an astrophysical scale,
something 500 times smaller than our Milky Way Galaxy.
ROWE: We call them ultra-compact dwarf galaxies,
or UCDs.
HOPKINS: You might imagine the difference between
the Milky Way Galaxy and a UCD as
the difference between a cloud and a rock,
where the rock is just the same kind of material,
but compressed to just incredibly high densities
compared to some fluffy gaseous thing.
ROWE: What are these strange galaxies?
They seem to break all the rules.
To find out, astronomers zoomed in to
a particularly dense,
ultra-compact dwarf galaxy
called M60-UCD1.
M60-UCD1 is 300 light-years across.
It's tiny. It's a pinpoint compared to
our enormous galaxy.
Our galaxy has 200 or more billion stars in it.
And M60-UCD1 only has 140 million.
But they're packed into this incredibly tight volume.
ROWE: The night sky inside the galaxy
would look very different from our own.
PLAIT: On Earth, when you look at the night sky,
you see a few thousand stars.
But if you were in M60-UCD1,
you wouldn't just see a few thousand stars.
You would see hundreds of thousands of stars
in the night sky. That would be amazing.
ROWE: As the astronomers look deeper
into the heart of this tiny galaxy,
Things got even weirder.
They found a supermassive black hole much bigger
than expected.
It actually has a black hole that's bigger, five times bigger
than the black hole at the center of
our Milky Way Galaxy.
PLAIT: When we see supermassive black holes inside of galaxies,
they tend to scale with the size of the galaxy itself.
A bigger galaxy has a bigger supermassive black hole.
Why does such a tiny little object
have such an oversized central black hole?
ROWE: The only possible explanation?
This tiny galaxy was once much larger.
These galaxies might have begun their lives as, in fact,
much bigger galaxies.
And that what we see today, it was really just the very
central, densest part of a much larger galaxy
ROWE: Based on the size of its supermassive black hole,
M60-UCD1 may once
have contained many billions of stars.
Something captured them,
and we don't have to look far to find the aggressor --
A nearby super galaxy with
lots of gravitational firepower -- M60.
M60 is a monster. It has a trillion stars in it.
It's bigger than the Milky Way,
and we're pretty big.
ROWE: The battle was not a full-on frontal assault.
M60 raided its smaller opponent, capturing its troops.
SUTTER: This is more of a stealthy guerrilla hit and run
where we're gonna move in,
pick off some of your troops, and then get out
before you even notice.
MINGARELLI: All that's left from one of these drive-by
galaxy interactions
is this supermassive black hole with a fraction
of its original stars.
ROWE: The conflict devastated M60-UCD1.
Over 98% of its stellar army were captured
and became prisoners of war.
SUTTER: It used to be a big galaxy,
but it suffered one too many defeats.
And now it's a -- It's a fallen empire.
PLAIT: We can frame this battle
between M60 and M60-UCD1 as just a battle.
But in fact, it's a slaughter.
It's a massacre.
SUTTER: These small galaxies get all their troops removed,
but the HQ,
the supermassive black hole remains,
but it doesn't have any troops left.
ROWE: Eventually, M60 will conquer its battered opponent,
destroying what's left of the compact galaxy.
PLAIT: It'll get ripped apart even further,
and more and more stars will be consumed
by the bigger galaxy.
So chances are this little dwarf is eventually going to
be pulled apart and become a part of M60.
ROWE: In the great game of galactic warfare,
losing can be catastrophic.
For weak and small galaxies,
resistance is futile.
Pillaged for resource is by their more powerful opponents,
they slowly become burnt-out wrecks.
But some peaceful galaxies face an equally terrible fate.
They starve to death.
ROWE: Cosmic wars are vicious.
They destroy many galaxies,
but violent conflicts can also give galaxies new life.
Case in point,
galaxy NGC 4485.
HOPKINS: NGC 4485 has a nickname of the two-faced galaxy,
like the Batman villain,
because it has two different halves of the galaxy
doing completely different things.
Half of the galaxy is sort of old and calm
and relatively quiescent,
whereas half of it appears to be undergoing a sort of
fireworks display of new star formation.
ROWE: Why are new stars only born
in one half of this galaxy?
We found a clue on the edge of
a photo taken by the Hubble Space Telescope.
It was evidence of an attack by another galaxy.
We think that another galaxy passed through it just off
center in a way that strongly perturbed
the gas on one half of the galaxy.
ROWE: The two-faced galaxy skirmish gave it
a gravitational jolt,
forcing clouds of gas together.
When we think of galaxies, we think of stars,
and of course, galaxies are made of stars.
But, of course, gas is the stuff that
stars are made of.
ROWE: When two galaxies collide,
the gravitational duel can trigger
a huge burst of star formation.
You need something to give a galaxy a push,
and that's exactly what a galaxy collision does.
BASRI: And when gas clouds collide, they compress.
And when they compress, you get knots in them that can
compress more and form stars.
So you can think of these collisions as very
violent events,
but ultimately, it can breathe new life into a galaxy.
ROWE: But the spoils of war don't last long.
SUTTER: In the short term, the victor galaxy can
come out glorious with -- With so many new stars.
But this celebration is short-lived, because that round
of star formation quickly uses up the material available.
If a galaxy wants to stay alive, it has to feed on
other galaxies.
ROWE: So galaxies constantly need to raid new targets,
and that raises an important question.
What happens if there's a galaxy just alone in space?
Nothing else is colliding with it, sort of a pacifist galaxy.
ROWE: The poster child for these peace-loving galaxies
is NGC 1277.
STRAUGHN: NGC 1277 is a very peculiar galaxy.
It's pretty big, and its stars are extremely old.
HOPKINS: It basically hasn't formed new stars in the last
10 billion years,
so it's kind of the veterans home of galaxies.
ROWE: NGC 1277 lives in a rough
part of the cosmos called the Perseus Cluster.
Thousands of other galaxies surround NGC 1277,
and they are all ready for a fight.
So you might ask, why hasn't it had
encounters with other galaxies that might rejuvenate it?
ROWE: The answer, once again, is gravity.
NGC 1277 sits inside this massive galaxy cluster
that has a ton of mass,
and if you look at its position, it's fairly near
the center of the cluster.
ROWE: The combined gravity of thousands of galaxies
pulls on NGC 1277,
accelerating it to two million miles an hour.
STRAUGHN: And so it has spent the last
few billion years traveling faster and faster.
Until now, it's almost at its fastest pace.
HOPKINS: It's very hard for gravity
to catch it or catch one of its neighbors
and bring them together to merge with each other.
ROWE: NGC 1277 has no chance of
grabbing new gas to make new stars.
It's dying. All that has left are old red stars.
SUTTER: When it comes to galaxies, red is dead.
No new stars means no big stars,
no blue stars, just small dim red dwarfs.
ROWE: Galaxies that don't fight just fade away.
THALLER: And at that point, the history of
the universe becomes really kind of boring.
All the stars will simply start to die out.
Eventually, there will be the last
star formed in the Milky Way,
with no new galaxy bringing fresh material.
Without galaxy collisions, the universe dies.
♪♪
ROWE: Galactic battles mix things up
and replenish gas supplies,
and our own galaxy has reaped the benefits.
Our Milky Way Galaxy fought a massive battle,
but that battle may have been necessary to build
solar systems like the one we live in right now.
ROWE: Clashes with the Sagittarius Dwarf Galaxy
occurred at the same time the sun formed.
BULLOCK: It's possible that we owe our very
existence to the collision with the Sagittarius Dwarf Galaxy.
TREMBLAY: Maybe the gas that ultimately gave rise
to the birth of our solar system
once came from another galaxy entirely.
ROWE: So galactic wars are both creative and destructive.
Galaxies are built from collisions,
galaxies survive from collisions,
and galaxies can also die from collisions.
Far from being destructive events,
colliding galaxies may be the reason
that you and I are here.
ROWE: Intergalactic warfare has revolutionized
our understanding of how galaxies live and die.
Ultimately, it's these galaxy mergers that are one of
the great engines of all structure growth
in the universe.
OLUSEYI: These collisions got us to where we are today,
and they're gonna determine the future of all the universe.