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Our universe is at war.

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The universe is a very violent
and deadly place.

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Entire galaxies
fight to the death.

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Talk about clash of the Titans.

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It doesn't get more titanic
than this.

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It's a slaughter.
It's a massacre.

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Only the strongest survive.

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If a galaxy wants to stay alive,

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it has to feed on
other galaxies.

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Our own galaxy
also fights for survival.

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We are facing
the ultimate destruction

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of the Milky Way Galaxy.

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These battles are
how galaxies live,

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grow, and die.

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These collisions got us to
where we are today,

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and they're going to determine
the future of the universe.

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In 2018,
astronomers used the Gaia

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space telescope to map
our Milky Way Galaxy.

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They tracked the movements of
a billion stars,

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and they found that some
behave very strangely.

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When astronomers were
mapping stars in our galaxy,

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they found a whole bunch that
we're on similar

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but very strange orbits.

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Most stars of the Milky Way
are orbiting in a sort of

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regular pattern, but these stars

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at the center, they're in
these highly elongated orbits.

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Coming in from very far,

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swinging around the center of
our galaxy, and then going back

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out again, a little bit
like a comet does.

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This group of stars plunges

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wildly through
the center of our galaxy.

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When you track their direction
and speed on a chart,

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you get a shape that looks
a bit like a sausage.

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This doesn't sound
very science-y,

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but this sausage is really
what the stars look like

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if you look at the shapes

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of their orbits
in a certain configuration.

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What sent so many
stars on such a strange path?

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It must have been a huge event.

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We think these stars are
the result of a past

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cosmic collision.

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They are casualties
from an enormous battle between

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the Milky Way
and a foreign galactic army.

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They don't move
like stars in the Milky Way,

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because they're not
from the Milky Way.

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These stars are
actually alien stars.

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They're invaders from outer,
outer space.

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The attackers left
their mark on the Milky Way.

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We find similar battle scars
on galaxies across

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the universe.

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Our models of galaxy
information are still

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pretty uncertain.

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We still don't really
understand how galaxies got to

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where they are, how we go from
the Big Bang to the Milky Way.

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Wars between galaxies
have profound consequences, for

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the winners,
the losers, and for us.

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What we're learning is that
these galactic battles have had

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a huge impact on what
the universe looks like today.

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Our understanding
of galaxies has changed

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entirely in the last
few decades.

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We understand now that every
big galaxy like the Milky Way

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started from many smaller
things colliding,

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changing each other
as they went.

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Nearly 10 billion years ago,

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the sausage stars were part of
a foreign galaxy.

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It was on a collision course
with our home, the Milky Way.

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We call this invading army
the Sausage Galaxy,

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or Gaia-Enceladus.

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The galaxy that
we fought probably had

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about 50 billion stars,

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so we're talking about
something that is a significant

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fraction of the size of
the Milky Way.

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Gaia-Enceladus
was a tough opponent,

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but the Milky Way
was 20 times its mass,

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and that makes
a huge difference.

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When galaxies interact
with each other,

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size definitely matters.

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The bigger galaxies are gonna
dominate over the smaller ones,

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ripping them apart and
essentially consuming them.

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Galaxy interactions
are all about bullies.

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The bigger you are,
the badder you are.

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When two galaxies collide,

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it's like two massive armies
marching towards each other.

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These galaxies aren't fighting

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with knives or spears
or guns or even nuclear bombs.

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They're fighting with something

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much more powerful...
Gravity itself.

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Each galaxy contains
billions of stars and planets

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and a supermassive black hole,

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millions of times
the mass of the sun.

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That's a lot of
gravitational firepower.

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As these galaxies
approach each other,

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you can get tidal effects...
The same way that the moon can

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raise tides on one side of
the Earth and the opposite side,

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one galaxy can stretch another

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galaxy along
a certain direction.

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As Gaia-Enceladus
advanced towards us,

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our galaxy's superior
gravity grabbed

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hold of the smaller galaxy.

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As it approached, the gravity
from the Milky Way

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would have stretched it out.

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Gaia-Enceladus was
distorted but not defeated.

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The battle was just beginning.

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It would have passed
through our galaxy,

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maybe orbiting a couple of
times before being torn

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apart by our gravity.

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The Milky Way's
gravitational power

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ripped Gaia-Enceladus apart

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and captured billions of
its stars.

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Eventually, most of those
stars would have

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then settled down into

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the disk of the Milky Way
and become a part of it.

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Little galaxy try
to take on the Milky Way...

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You're gonna get
what's coming to you.

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Despite winning the battle,

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the Milky Way suffered
serious damage.

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The collision
with the Sausage Galaxy

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left a scar on the Milky Way.

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And when we look near
the center of our galaxy,

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we see a bulge that's left
over from that collision.

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The Milky Way isn't
the only galaxy scarred by war.

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Across the universe,

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rival armies made up of
billions of stars slug it out,

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leaving behind distorted
and damaged casualties of war.

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There's a million different

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sub-categories of them.

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There's tadpole galaxies
that have long tails,

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longer than our own galaxy.

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There are things like
Arp-Madore 2026, where you see

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this eerie, glowing face,

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two big eyes looking right at
you from across the universe.

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There are galaxies that looked
like they might have collided

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with one another and blown
holes through each other.

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These battle scars
give us important clues

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about one of the biggest
mysteries in astronomy...

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How galaxies develop and grow.

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But there's a problem.

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We can't watch
these battles in real time.

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The scale of galaxies is huge.

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They're hundreds of thousands
of light years across.

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It's going to take them millions

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or billions of years
to come together.

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So it's like looking at
one frame

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from a really energetic
fight scene in a movie.

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By piecing these
snapshots together,

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astronomers can build up
a detailed picture of past

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conflicts and discover how
these battles transformed

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galaxies over billions of years.

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We have pictures of
isolated galaxies,

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we have pictures of
interacting galaxies,

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and we have pictures of
aftermath galaxies.

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And that's helped us
discover something alarming.

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The Milky Way faces yet
another attack from

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an enemy armed with
an enormous secret weapon.

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Will our solar system
survive the onslaught?

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Across the universe,

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galaxies are at war,

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Their main weapon...

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Gravity.

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It tears the combatants into
weird and wonderful shapes.

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Our galaxy didn't
escape the mayhem.

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It's peppered with battle scars.

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The overall shape
of the Milky Way

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is a flat disk of stars and gas.

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Except recently, we have found
out that at the edges,

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it's actually warped a little
bit like the brim of a fedora.

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The stars actually dip down
below the plane on

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one side and dip above it
on the other.

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We think the attacker
was one of our satellites,

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a galaxy that orbits
the Milky Way like the moon

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orbits the Earth.

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It's called the Sagittarius
Dwarf Galaxy.

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From looking at how
the stars move in the Milky Way,

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we suspect that
the Sagittarius Dwarf Galaxy has

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actually crashed through
the Milky Way a few times on

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its course of its orbit
around the galaxy.

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It came in
about six billion years ago,

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hit the disk hard about two
billion years ago, and crashed

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again about a billion years ago.

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And our gravity has
pulled it out into a gigantic,

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looping stream of stars that
is moving in and out

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of our Milky Way.

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The war is not over.

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The insurgent galaxy
will return.

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When galaxies interact,

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often they're caught in this
huge cosmic dance

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where they revolve around
each other a few times,

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or they even crash through
each other and then come

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back around.

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The Sagittarius Dwarf Galaxy
looks like

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it's crashing in with ever
increasing frequency.

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A new skirmish could
take place in the next

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100 million years.

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So should we be worried
about these attacks?

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Because the Sagittarius
Dwarf Galaxy is so small

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compared to the Milky Way,

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it will do some damage at
the beginning,

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but because we're so massive,
we can absorb the impact.

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I mean, this galaxy,
it's looking for a fight,

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but it's also 10,000 times
smaller than us.

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So this is gonna be
no sweat at all.

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So far, the Milky Way
has been victorious.

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But the danger isn't over.

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We are surrounded by enemies.

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Our local
neighborhood of galaxies

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has three major galaxies,

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but up to 50 smaller ones.

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All these galaxies are
potential troublemakers.

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Each one of these could be
armies that rise up against us.

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The two most famous
galaxies that orbit

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the Milky Way are the Large
and Small Magellanic Clouds.

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These are two independent
dwarf galaxies that you can

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see in the night sky from
the Southern Hemisphere.

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We thought the Large
Magellanic Cloud orbited

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our galaxy at a safe distance
of 160,000 light years.

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We thought it would
stay that way,

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and we thought it was harmless.

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Now, a new discovery shows
we were wrong on all counts.

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The new factor that changed our
view of the Magellanic Cloud

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is we found out

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it has a lot more
dark matter than we thought.

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Dark matter,

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the most mysterious stuff
in the universe.

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A dark matter is literally
what it sounds like.

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It's matter that we cannot see.

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But it has gravity and can
affect objects

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that we can see.

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Adding in this extra
dark matter makes the Large

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Magellanic Cloud at least
twice a massive as predicted.

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So its gravity is double
what we thought.

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It's secretly been gathering

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allies, has been gathering
dark matter on its side,

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and now it's a much bigger
threat than we thought before.

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So it's not just
going to orbit us.

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It's gonna collide
with the Milky Way.

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Moving at nearly
a million miles an hour,

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the Large Magellanic Cloud
will not swing past us.

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It will attack.

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The large Magellanic Cloud is

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1/10 the mass of the Milky Way.

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That's enough to make
a pretty big punch.

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In about 2.5 billion years,

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it will smash into our galaxy.

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It's gonna plow through
the disk of the Milky Way,

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it's gonna blow a cavity.

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It might even damage
our spiral arms.

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Earth sits in one of
those spiral arms.

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Could our planet become
collateral damage?

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If the Large Magellanic Cloud
passes through the plane

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of our galaxy near our location,

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that can have dire consequences.

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The gravitational clash between

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the invader on the Milky Way

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00:14:09,260 --> 00:14:12,370
could hurl stars and
planets out of our galaxy.

255
00:14:14,240 --> 00:14:16,100
Earth could be one of them.

256
00:14:17,740 --> 00:14:20,540
Our planet's very
close to its own star,

257
00:14:20,640 --> 00:14:23,840
so the odds are that you'll
just get ripped out

258
00:14:23,950 --> 00:14:25,110
along with your star,

259
00:14:25,210 --> 00:14:28,150
so we'd be moving along with
the sun even as the sun gets

260
00:14:28,250 --> 00:14:30,890
jettisoned from our galaxy.

261
00:14:30,990 --> 00:14:33,720
And it'll move off out
into intergalactic space.

262
00:14:33,820 --> 00:14:35,520
And that's not terrible.

263
00:14:35,620 --> 00:14:37,390
I mean, it's not gonna
get destroyed,

264
00:14:37,490 --> 00:14:38,730
but it's a little lonely.

265
00:14:42,030 --> 00:14:44,500
Our view of the night sky

266
00:14:44,600 --> 00:14:46,000
would radically change.

267
00:14:47,600 --> 00:14:50,470
We'd be able to see
much more of the Milky Way,

268
00:14:50,570 --> 00:14:54,240
especially if we got kicked up
above the plane of the galaxy.

269
00:14:54,340 --> 00:14:56,810
We'd be able to see
the whole shebang.

270
00:14:56,910 --> 00:15:00,550
Just look at any image of
a spiral galaxy.

271
00:15:00,650 --> 00:15:03,780
They're gorgeous.
Now imagine seeing your night

272
00:15:03,890 --> 00:15:07,350
sky filled with
a face-on spiral galaxy.

273
00:15:07,460 --> 00:15:09,920
That would be like
waking up to my face

274
00:15:10,030 --> 00:15:12,830
every morning... spectacular.

275
00:15:17,470 --> 00:15:19,970
If we were unlucky,

276
00:15:20,070 --> 00:15:21,640
our home planet could have

277
00:15:21,740 --> 00:15:25,040
a close encounter with
an invading star.

278
00:15:25,140 --> 00:15:28,940
The odds are very low
that another star

279
00:15:29,040 --> 00:15:30,740
will pass close by the sun,

280
00:15:30,850 --> 00:15:32,780
but those odds aren't zero.

281
00:15:32,880 --> 00:15:34,580
It could happen
that another star

282
00:15:34,680 --> 00:15:36,750
passes close enough
to affect the planets.

283
00:15:36,850 --> 00:15:38,520
And if that were to happen,

284
00:15:38,620 --> 00:15:43,560
it could upset the delicate
balance in the solar system.

285
00:15:44,590 --> 00:15:47,800
We don't know where
the Earth could end up.

286
00:15:47,900 --> 00:15:49,860
It might find its way
into the sun.

287
00:15:49,970 --> 00:15:51,000
You just don't know.

288
00:15:51,100 --> 00:15:52,870
Or there might just be a rain

289
00:15:52,970 --> 00:15:55,400
of comets into
our inner solar system.

290
00:15:55,500 --> 00:15:57,940
Our own planet
might be flung out,

291
00:15:58,040 --> 00:16:01,240
in which case, this would be
a death knell for all life

292
00:16:01,340 --> 00:16:02,580
on Earth.

293
00:16:02,680 --> 00:16:05,280
I'm not someone who is like
a doom and gloom person,

294
00:16:05,380 --> 00:16:07,180
but, like, that would be insane.

295
00:16:08,520 --> 00:16:10,080
You don't know
what's gonna happen,

296
00:16:10,190 --> 00:16:13,350
but most of the options are bad.

297
00:16:13,460 --> 00:16:16,660
All these nightmare scenarios

298
00:16:16,760 --> 00:16:18,490
will extinguish life.

299
00:16:22,130 --> 00:16:25,000
Earth might survive,
but our cosmic

300
00:16:25,100 --> 00:16:27,630
zip code will take
a severe beating.

301
00:16:29,240 --> 00:16:31,440
The Milky Way Galaxy
is bigger than

302
00:16:31,540 --> 00:16:32,640
the Large Magellanic Cloud,

303
00:16:32,710 --> 00:16:35,440
so we are gonna win,
[exhales heavily]

304
00:16:35,540 --> 00:16:37,340
but it's gonna hurt us
for a long time.

305
00:16:39,050 --> 00:16:40,610
The Large Magellanic Cloud

306
00:16:40,720 --> 00:16:42,680
will leave our galaxy battered,

307
00:16:42,780 --> 00:16:45,750
bruised,
but ultimately undefeated.

308
00:16:45,850 --> 00:16:49,760
But there's a far bigger
threat looming

309
00:16:49,860 --> 00:16:51,590
over the Milky Way.

310
00:16:51,690 --> 00:16:54,630
It's gonna face an opponent
that it can't defeat.

311
00:16:56,000 --> 00:16:58,200
Will this mega collision be

312
00:16:58,300 --> 00:17:00,600
the Milky Way's last stand?

313
00:17:11,650 --> 00:17:13,150
For billions of years,

314
00:17:13,250 --> 00:17:16,250
the Milky Way conquered
galaxy after galaxy,

315
00:17:16,350 --> 00:17:19,850
tearing its smaller rivals
to pieces.

316
00:17:21,120 --> 00:17:24,090
But our galaxy is about
to meet its match.

317
00:17:27,130 --> 00:17:31,100
In the not-too-distant future,
galactically speaking,

318
00:17:31,200 --> 00:17:34,840
a much, much larger battle
is due for the Milky Way.

319
00:17:36,540 --> 00:17:38,940
A battle
with a local superpower,

320
00:17:40,240 --> 00:17:41,540
the Andromeda Galaxy.

321
00:17:43,110 --> 00:17:46,750
We thought this huge galaxy
might wound us in the future.

322
00:17:48,180 --> 00:17:51,720
Now, recent evidence reveals
it's going to make

323
00:17:51,820 --> 00:17:54,490
a full-scale assault.

324
00:17:54,590 --> 00:17:58,130
We've known for a long time
that Andromeda is heading

325
00:17:58,230 --> 00:18:00,390
more or less toward us,

326
00:18:00,500 --> 00:18:02,860
but we didn't know exactly
in what direction.

327
00:18:02,960 --> 00:18:04,570
But in recent years, we've been

328
00:18:04,670 --> 00:18:06,670
able to pinpoint
this a lot better.

329
00:18:06,770 --> 00:18:10,370
And, uh, yeah, it's...
It's heading right for us.

330
00:18:13,110 --> 00:18:16,180
Data from the Hubble
Space Telescope shows

331
00:18:16,280 --> 00:18:20,180
two galaxies will collide in
about four billion years,

332
00:18:23,020 --> 00:18:26,890
and it will be
a monumental battle.

333
00:18:26,990 --> 00:18:30,890
This collision that is coming,
and it is coming, is not gonna

334
00:18:30,990 --> 00:18:33,430
be anything like the Milky Way
has experienced before

335
00:18:33,530 --> 00:18:35,630
in its 10-
or 12-billion-year history.

336
00:18:35,730 --> 00:18:38,330
This is a galaxy of
comparable size.

337
00:18:38,430 --> 00:18:42,740
This is two heavyweight prize
fighters coming at it.

338
00:18:42,840 --> 00:18:46,940
Warriors with the same
gravitational firepower.

339
00:18:47,040 --> 00:18:50,810
Simulations suggest
a clash of the Titans.

340
00:18:50,910 --> 00:18:53,350
Each of them with half
a trillion stars in them.

341
00:18:53,450 --> 00:18:55,920
That sounds like a pretty
spectacular collision.

342
00:18:57,990 --> 00:19:00,920
Fights between
equally matched galaxies

343
00:19:01,020 --> 00:19:03,520
are rare and messy.

344
00:19:03,630 --> 00:19:05,590
When the battle kicks off,

345
00:19:05,690 --> 00:19:08,600
there will be no good news
for either side.

346
00:19:10,770 --> 00:19:13,400
When the Andromeda Galaxy
and the Milky Way Galaxy

347
00:19:13,500 --> 00:19:14,870
start to get close,

348
00:19:14,970 --> 00:19:16,540
they're gonna start
affecting each

349
00:19:16,640 --> 00:19:17,700
other profoundly.

350
00:19:17,810 --> 00:19:20,070
Tendrils of stars are gonna be
thrown out.

351
00:19:20,180 --> 00:19:23,980
Gas is gonna be thrown out.

352
00:19:24,080 --> 00:19:26,580
It won't be a single impact.

353
00:19:26,680 --> 00:19:29,620
Gravity will send
the two opponents

354
00:19:29,720 --> 00:19:32,450
into a spiraling dance of death.

355
00:19:34,620 --> 00:19:36,890
The first pass is
actually not a direct hit.

356
00:19:36,990 --> 00:19:39,690
They're gonna swing past
each other, in fact.

357
00:19:39,790 --> 00:19:42,200
And at this point,
their gravitational

358
00:19:42,300 --> 00:19:43,800
interaction is gonna
slow them down,

359
00:19:43,900 --> 00:19:46,030
and they're gonna come
back toward each other.

360
00:19:46,130 --> 00:19:49,670
The galaxies will
collide and fly apart again,

361
00:19:49,770 --> 00:19:54,310
inflicting more and more
damage with each clash.

362
00:19:54,410 --> 00:19:56,940
If you were to go
outside and look up,

363
00:19:57,050 --> 00:20:00,050
you could see the disk of our
galaxy getting ripped apart

364
00:20:00,150 --> 00:20:02,320
by tidal interactions
with Andromeda.

365
00:20:05,990 --> 00:20:09,320
The two beautiful
spiral galaxies

366
00:20:09,420 --> 00:20:11,730
will tear each other apart,

367
00:20:11,830 --> 00:20:16,360
leaving one vast
elliptical galaxy.

368
00:20:18,300 --> 00:20:21,370
The fate of
the Andromeda, Milky Way

369
00:20:21,470 --> 00:20:24,710
battle is that they will merge.

370
00:20:24,810 --> 00:20:28,410
This is going to be
one gigantic galaxy.

371
00:20:31,480 --> 00:20:32,750
And that presents a problem.

372
00:20:32,850 --> 00:20:34,510
What are we gonna
call this new galaxy?

373
00:20:34,620 --> 00:20:37,580
Of course, my nerd colleagues
have come up with

374
00:20:37,690 --> 00:20:40,520
names like Milkomeda,
Andromeway.

375
00:20:40,620 --> 00:20:42,760
Whatever, those are corny.

376
00:20:42,860 --> 00:20:44,890
We should just call it Hakeem.

377
00:20:50,970 --> 00:20:53,500
With a trillion stars,
it will be

378
00:20:53,600 --> 00:20:56,440
one of the biggest galaxies
in the universe.

379
00:20:58,970 --> 00:21:00,140
In the Hakeem Galaxy,

380
00:21:00,240 --> 00:21:02,280
things gonna be completely new.

381
00:21:02,380 --> 00:21:05,680
First off, it's gonna be
a really good-looking galaxy.

382
00:21:05,780 --> 00:21:07,510
Let's get that straight
from the get-go.

383
00:21:07,620 --> 00:21:12,650
Second, it's gonna be powerful,
and I'm talking powerful.

384
00:21:12,750 --> 00:21:14,390
This may be the most remarkable

385
00:21:14,490 --> 00:21:16,590
galaxy in the history
of the universe.

386
00:21:19,130 --> 00:21:23,100
Milkomeda, or Hakeem,
if you prefer,

387
00:21:23,200 --> 00:21:26,570
will become the undisputed boss
of our cosmic neighborhood.

388
00:21:26,630 --> 00:21:30,140
It's calm appearance concealing

389
00:21:30,240 --> 00:21:31,810
a history of violence.

390
00:21:34,840 --> 00:21:37,980
It's the result of a complete
war zone of mergers over

391
00:21:38,080 --> 00:21:39,326
the course of billions of years,

392
00:21:39,350 --> 00:21:42,350
many galaxies crashing
together, fully reconfiguring

393
00:21:42,450 --> 00:21:44,520
each time and slowly, you grow

394
00:21:44,620 --> 00:21:48,190
this smooth, placid,
big blob of stars.

395
00:21:50,260 --> 00:21:53,090
After billions
of years of warfare,

396
00:21:53,190 --> 00:21:56,160
our galaxy will finally
be peaceful.

397
00:21:58,770 --> 00:22:02,600
But before it's honorable
discharge, Milkomeda

398
00:22:02,700 --> 00:22:04,770
may produce one final,

399
00:22:04,870 --> 00:22:07,640
devastating act of war.

400
00:22:07,740 --> 00:22:11,910
Imagine World War II,
and then all of a sudden,

401
00:22:12,010 --> 00:22:14,880
one of the sides comes
up with the Death Star.

402
00:22:14,980 --> 00:22:16,520
That's what
we're talking about here.

403
00:22:19,090 --> 00:22:21,420
A weapon of cosmic destruction.

404
00:22:37,810 --> 00:22:40,040
When giant galaxies clash,

405
00:22:40,140 --> 00:22:43,110
the battles are spectacular
and destructive.

406
00:22:46,280 --> 00:22:50,420
The victors steal huge numbers
of stars and vast amounts

407
00:22:50,520 --> 00:22:55,290
of gas as fuel
for the ultimate super weapon.

408
00:22:57,360 --> 00:23:00,230
The special weapon
that these monster galaxies

409
00:23:00,330 --> 00:23:03,460
have is a giant Death Ray,

410
00:23:03,560 --> 00:23:08,440
a jet of material racing across
thousands of light-years.

411
00:23:10,840 --> 00:23:13,540
These huge outbursts
of energy blast out

412
00:23:13,640 --> 00:23:16,710
of the center of
the colliding galaxies.

413
00:23:16,810 --> 00:23:20,050
They produce more energy
in one second than

414
00:23:20,150 --> 00:23:25,190
the sun will in its entire
10-billion-year lifetime.

415
00:23:25,290 --> 00:23:27,220
We call them jets.

416
00:23:28,990 --> 00:23:33,160
These incredibly powerful jets
aren't just brief features.

417
00:23:33,260 --> 00:23:36,400
They can be sustained
for millions of years,

418
00:23:36,500 --> 00:23:38,570
and they can maintain
their structure

419
00:23:38,670 --> 00:23:41,500
for thousands of light-years.

420
00:23:41,600 --> 00:23:43,470
It's like turning on
a garden hose

421
00:23:43,570 --> 00:23:45,870
in Chicago and using it to water

422
00:23:45,970 --> 00:23:47,610
a garden in London.

423
00:23:49,580 --> 00:23:52,580
Exactly what triggered
these jets was a mystery.

424
00:23:52,680 --> 00:23:57,120
Then, in June 2018,
astronomers in Hawaii captured

425
00:23:57,220 --> 00:24:00,350
something stunning...
A jet forming

426
00:24:00,460 --> 00:24:02,860
during a galactic collision.

427
00:24:05,430 --> 00:24:07,590
The team found something
really incredible.

428
00:24:07,700 --> 00:24:11,030
They found two galaxies that
were in a cosmic collision

429
00:24:11,130 --> 00:24:14,330
and actually found an active
jet in one of these galaxies.

430
00:24:14,440 --> 00:24:16,840
It was the first time anything
like this has been discovered.

431
00:24:20,340 --> 00:24:23,980
When galaxies collide,
the clash drives huge clouds

432
00:24:24,080 --> 00:24:27,480
of gas and dust towards
their centers.

433
00:24:27,580 --> 00:24:31,180
The supermassive black holes
start to feed.

434
00:24:33,390 --> 00:24:35,590
The gas that was in
those galaxies starts to

435
00:24:35,690 --> 00:24:39,390
funnel toward the black hole
and then fall upon it.

436
00:24:39,490 --> 00:24:42,030
Not all this gas ends up inside

437
00:24:42,130 --> 00:24:44,160
the supermassive black hole.

438
00:24:44,270 --> 00:24:46,670
Powerful magnetic fields carry
some of

439
00:24:46,770 --> 00:24:49,500
this matter to the poles

440
00:24:49,600 --> 00:24:52,740
and blast it out
in tight, narrow jets.

441
00:24:52,840 --> 00:24:55,780
A super weapon is born.

442
00:24:55,880 --> 00:24:57,780
This discovery helps
us understand

443
00:24:57,880 --> 00:25:01,850
how giant elliptical
galaxies form.

444
00:25:01,950 --> 00:25:05,520
Knowing that mergers of spiral
galaxies can cause

445
00:25:05,650 --> 00:25:07,220
these jets helps us put together

446
00:25:07,320 --> 00:25:09,820
a complete picture of
how these huge elliptical

447
00:25:09,920 --> 00:25:11,420
galaxies might be formed.

448
00:25:14,430 --> 00:25:18,230
The discovery doesn't
answer all our questions.

449
00:25:18,330 --> 00:25:19,630
There's another mystery.

450
00:25:19,730 --> 00:25:21,970
How did the super giant
galaxies that

451
00:25:22,070 --> 00:25:25,070
dwarf the Milky Way get so big?

452
00:25:25,170 --> 00:25:29,380
Our Milky Way Galaxy is big-ish.

453
00:25:29,480 --> 00:25:31,550
It's... it's slightly
bigger than average,

454
00:25:31,650 --> 00:25:33,880
but IC 1101, for example,

455
00:25:33,980 --> 00:25:37,650
is more than 50 times larger
than our home galaxy and has

456
00:25:37,750 --> 00:25:42,020
more than a trillion, with a T,
a trillion stars in it.

457
00:25:42,120 --> 00:25:47,190
The biggest galaxies make
the Milky Way look like an ant.

458
00:25:47,300 --> 00:25:50,900
These galactic giants
pose a problem.

459
00:25:51,000 --> 00:25:53,500
There hasn't been enough time
since the birth of

460
00:25:53,600 --> 00:25:57,740
the universe
for them to become so large,

461
00:25:57,840 --> 00:26:00,110
even by conquering
smaller galaxies.

462
00:26:00,210 --> 00:26:03,240
When we look into
the distant universe,

463
00:26:03,340 --> 00:26:06,550
we see something very strange
that we don't quite understand.

464
00:26:06,650 --> 00:26:09,620
We see enormous galaxies
that existed just

465
00:26:09,720 --> 00:26:11,520
a billion years
after the Big Bang.

466
00:26:11,620 --> 00:26:14,650
And even though these cosmic
collisions help explain how

467
00:26:14,760 --> 00:26:16,020
galaxies get bigger,

468
00:26:16,120 --> 00:26:18,960
they don't quite explain
everything about how galaxies

469
00:26:19,060 --> 00:26:20,090
grow over time.

470
00:26:20,190 --> 00:26:22,360
So we still have a big mystery
on our hands here.

471
00:26:26,230 --> 00:26:29,800
So in 2019,
an international team

472
00:26:29,900 --> 00:26:32,370
investigated a very large galaxy

473
00:26:32,470 --> 00:26:35,410
over 300 million
light-years away.

474
00:26:35,510 --> 00:26:39,610
We call it NGC 6240.

475
00:26:39,710 --> 00:26:43,120
NGC 6240 was being
studied because

476
00:26:43,220 --> 00:26:45,790
it had two supermassive
black holes in it.

477
00:26:45,890 --> 00:26:48,090
Now the galaxy itself
looked like it

478
00:26:48,160 --> 00:26:50,160
had been disturbed,
like something had happened.

479
00:26:50,260 --> 00:26:53,730
They thought that potentially
it had had a recent merger.

480
00:26:59,300 --> 00:27:01,270
They were expecting to see two

481
00:27:01,370 --> 00:27:05,270
supermassive black holes
in the galaxy's heart.

482
00:27:05,370 --> 00:27:08,270
As the researchers peered
through the layers of gas

483
00:27:08,380 --> 00:27:12,450
and dust, they discovered
something surprising.

484
00:27:12,550 --> 00:27:14,710
What we found was staggering.

485
00:27:14,820 --> 00:27:17,380
We found not two but three

486
00:27:17,490 --> 00:27:20,250
supermassive black holes
lurking in the center.

487
00:27:26,630 --> 00:27:27,830
It's the first time we found

488
00:27:27,930 --> 00:27:32,430
a galaxy with three
supermassive black holes,

489
00:27:32,530 --> 00:27:36,000
evidence of
a three-galaxy pile up.

490
00:27:36,100 --> 00:27:40,140
This galaxy is an active
battlefield of

491
00:27:40,240 --> 00:27:46,110
not two but three armies
colliding at once,

492
00:27:46,210 --> 00:27:47,950
and because there are three
armies involved,

493
00:27:48,050 --> 00:27:50,180
there are three galaxies
involved with

494
00:27:50,280 --> 00:27:53,520
three times as much mass,
three times as many stars,

495
00:27:53,620 --> 00:27:56,220
three times as much material,
and three times as

496
00:27:56,320 --> 00:27:58,490
much violence.

497
00:27:58,590 --> 00:28:01,460
This three-way battle
may explain how

498
00:28:01,560 --> 00:28:06,270
the largest galaxies
got so big so fast.

499
00:28:06,370 --> 00:28:08,130
It could be that galaxy mergers

500
00:28:08,240 --> 00:28:11,140
are more frequent than
what we thought previously,

501
00:28:11,240 --> 00:28:14,740
and therefore,
galaxies become more massive

502
00:28:14,840 --> 00:28:16,880
faster than previously expected.

503
00:28:18,910 --> 00:28:21,050
In the past, galaxies may have

504
00:28:21,150 --> 00:28:24,420
battled and collided
more often than today.

505
00:28:24,520 --> 00:28:28,250
Back then, galaxies were more
densely packed together.

506
00:28:29,820 --> 00:28:33,330
Our universe is expanding
as it ages, which means in

507
00:28:33,430 --> 00:28:35,430
the past, all the galaxies in

508
00:28:35,530 --> 00:28:37,930
the universe were
closer together,

509
00:28:38,030 --> 00:28:40,030
and that means they had
greater chance for their

510
00:28:40,130 --> 00:28:41,630
gravitational interactions to

511
00:28:41,740 --> 00:28:43,940
pull them together
and smash them together.

512
00:28:46,610 --> 00:28:49,610
The early universe was at war.

513
00:28:49,710 --> 00:28:52,650
Conflicts between galaxies
were common.

514
00:28:52,750 --> 00:28:56,220
They collided frequently
and grew quickly.

515
00:28:57,790 --> 00:29:01,820
But not every galaxy profited
from the carnage.

516
00:29:01,920 --> 00:29:04,690
Some brave galaxies
took on the big guns

517
00:29:04,790 --> 00:29:06,760
and nearly died as a result.

518
00:29:21,540 --> 00:29:24,180
When galaxies fight,
the big get bigger.

519
00:29:24,280 --> 00:29:28,410
More mass means more gravity,
the vital ingredient

520
00:29:28,520 --> 00:29:29,650
for victory.

521
00:29:31,820 --> 00:29:36,020
But galactic conflict doesn't
always result in growth.

522
00:29:36,120 --> 00:29:39,790
A strange new astronomical
object had

523
00:29:39,890 --> 00:29:41,260
scientists confused.

524
00:29:44,430 --> 00:29:46,730
They just looked
like stars from the ground.

525
00:29:46,830 --> 00:29:50,170
However, with the advent of
Hubble and beautiful

526
00:29:50,270 --> 00:29:51,970
space-based telescopes,

527
00:29:52,070 --> 00:29:56,080
it was possible to look at
these stars again and actually

528
00:29:56,180 --> 00:29:58,040
discover that
they were galaxies.

529
00:30:03,280 --> 00:30:04,650
They're kind of crazy.

530
00:30:04,750 --> 00:30:09,820
They're a huge number of stars,
but crammed into an incredibly

531
00:30:09,920 --> 00:30:12,030
tiny space
on an astrophysical scale,

532
00:30:12,130 --> 00:30:16,460
something 500 times smaller
than our Milky Way Galaxy.

533
00:30:16,560 --> 00:30:20,400
We call them
ultra-compact dwarf galaxies,

534
00:30:20,500 --> 00:30:21,840
or UCDs.

535
00:30:23,270 --> 00:30:25,770
You might imagine
the difference between

536
00:30:25,870 --> 00:30:29,980
the Milky Way Galaxy
and a UCD as

537
00:30:30,080 --> 00:30:33,280
the difference between
a cloud and a rock,

538
00:30:33,380 --> 00:30:36,720
where the rock is just
the same kind of material,

539
00:30:36,820 --> 00:30:39,250
but compressed to just
incredibly high densities

540
00:30:39,350 --> 00:30:41,590
compared to some fluffy
gaseous thing.

541
00:30:44,590 --> 00:30:46,860
What are these strange galaxies?

542
00:30:46,960 --> 00:30:49,560
They seem to break
all the rules.

543
00:30:49,660 --> 00:30:53,000
To find out,
astronomers zoomed in to

544
00:30:53,100 --> 00:30:54,700
a particularly dense,

545
00:30:54,800 --> 00:30:57,340
ultra-compact dwarf galaxy

546
00:30:57,440 --> 00:31:00,740
called M60-UCD1.

547
00:31:02,010 --> 00:31:05,980
M60-UCD1 is
300 light-years across.

548
00:31:06,080 --> 00:31:08,010
It's tiny.
It's a pinpoint compared to

549
00:31:08,120 --> 00:31:09,450
our enormous galaxy.

550
00:31:09,550 --> 00:31:13,020
Our galaxy has 200 or more
billion stars in it.

551
00:31:13,120 --> 00:31:16,390
And M60-UCD1
only has 140 million.

552
00:31:16,490 --> 00:31:20,390
But they're packed into this
incredibly tight volume.

553
00:31:20,490 --> 00:31:22,700
The night sky inside the galaxy

554
00:31:22,800 --> 00:31:25,570
would look very different
from our own.

555
00:31:25,670 --> 00:31:28,030
On Earth, when you look
at the night sky,

556
00:31:28,140 --> 00:31:30,370
you see a few thousand stars.

557
00:31:30,470 --> 00:31:32,770
But if you were in M60-UCD1,

558
00:31:32,870 --> 00:31:35,110
you wouldn't just see
a few thousand stars.

559
00:31:35,210 --> 00:31:38,210
You would see hundreds of
thousands of stars

560
00:31:38,310 --> 00:31:41,010
in the night sky.
That would be amazing.

561
00:31:47,520 --> 00:31:49,290
As the astronomers look deeper

562
00:31:49,390 --> 00:31:51,930
into the heart
of this tiny galaxy,

563
00:31:52,030 --> 00:31:55,230
Things got even weirder.

564
00:31:55,330 --> 00:31:58,930
They found a supermassive
black hole much bigger

565
00:31:59,030 --> 00:32:01,300
than expected.

566
00:32:01,400 --> 00:32:05,840
It actually has a black hole
that's bigger, five times bigger

567
00:32:05,940 --> 00:32:07,246
than the black hole at
the center of

568
00:32:07,270 --> 00:32:09,210
our Milky Way Galaxy.

569
00:32:09,280 --> 00:32:12,810
When we see supermassive
black holes inside of galaxies,

570
00:32:12,910 --> 00:32:16,220
they tend to scale with
the size of the galaxy itself.

571
00:32:16,320 --> 00:32:19,990
A bigger galaxy has a bigger
supermassive black hole.

572
00:32:20,090 --> 00:32:22,220
Why does such
a tiny little object

573
00:32:22,320 --> 00:32:25,760
have such an oversized
central black hole?

574
00:32:25,860 --> 00:32:27,960
The only possible explanation?

575
00:32:28,060 --> 00:32:32,700
This tiny galaxy
was once much larger.

576
00:32:32,800 --> 00:32:35,770
These galaxies might have
begun their lives as, in fact,

577
00:32:35,870 --> 00:32:37,840
much bigger galaxies.

578
00:32:37,940 --> 00:32:40,310
And that what we see today,
it was really just the very

579
00:32:40,410 --> 00:32:43,310
central, densest part
of a much larger galaxy

580
00:32:44,980 --> 00:32:48,310
Based on the size of
its supermassive black hole,

581
00:32:48,380 --> 00:32:51,320
M60-UCD1 may once

582
00:32:51,420 --> 00:32:54,320
have contained many
billions of stars.

583
00:32:54,420 --> 00:32:57,720
Something captured them,

584
00:32:57,830 --> 00:33:00,790
and we don't have to look far
to find the aggressor...

585
00:33:00,890 --> 00:33:03,100
A nearby super galaxy with

586
00:33:03,200 --> 00:33:07,730
lots of gravitational
firepower... M60.

587
00:33:07,840 --> 00:33:11,340
M60 is a monster.
It has a trillion stars in it.

588
00:33:11,440 --> 00:33:12,710
It's bigger than the Milky Way,

589
00:33:12,810 --> 00:33:14,570
and we're pretty big.

590
00:33:14,680 --> 00:33:18,010
The battle was not
a full-on frontal assault.

591
00:33:18,110 --> 00:33:23,380
M60 raided its smaller
opponent, capturing its troops.

592
00:33:23,480 --> 00:33:26,690
This is more of
a stealthy guerrilla hit and run

593
00:33:26,790 --> 00:33:28,290
where we're gonna move in,

594
00:33:28,390 --> 00:33:30,920
pick off some of your troops,
and then get out

595
00:33:31,030 --> 00:33:33,530
before you even notice.

596
00:33:33,630 --> 00:33:36,660
All that's left
from one of these drive-by

597
00:33:36,760 --> 00:33:38,030
galaxy interactions

598
00:33:38,130 --> 00:33:41,400
is this supermassive black
hole with a fraction

599
00:33:41,500 --> 00:33:43,470
of its original stars.

600
00:33:43,570 --> 00:33:48,370
The conflict
devastated M60-UCD1.

601
00:33:48,480 --> 00:33:51,980
Over 98% of its stellar army
were captured

602
00:33:52,080 --> 00:33:54,450
and became prisoners of war.

603
00:33:54,550 --> 00:33:57,750
It used to be a big galaxy,

604
00:33:57,850 --> 00:34:00,220
but it suffered
one too many defeats.

605
00:34:00,320 --> 00:34:02,620
And now it's a...
It's a fallen empire.

606
00:34:02,720 --> 00:34:05,090
We can frame this battle

607
00:34:05,190 --> 00:34:09,100
between M60 and M60-UCD1
as just a battle.

608
00:34:09,200 --> 00:34:11,330
But in fact, it's a slaughter.

609
00:34:11,430 --> 00:34:13,430
It's a massacre.

610
00:34:13,530 --> 00:34:17,570
These small galaxies get
all their troops removed,

611
00:34:17,670 --> 00:34:19,340
but the HQ,

612
00:34:19,440 --> 00:34:21,470
the supermassive
black hole remains,

613
00:34:21,580 --> 00:34:24,310
but it doesn't have
any troops left.

614
00:34:24,410 --> 00:34:28,050
Eventually, M60 will
conquer its battered opponent,

615
00:34:28,150 --> 00:34:32,590
destroying what's left of
the compact galaxy.

616
00:34:32,720 --> 00:34:34,320
It'll get ripped apart
even further,

617
00:34:34,420 --> 00:34:36,520
and more and more stars
will be consumed

618
00:34:36,620 --> 00:34:37,990
by the bigger galaxy.

619
00:34:38,090 --> 00:34:41,590
So chances are this little
dwarf is eventually going to

620
00:34:41,700 --> 00:34:45,530
be pulled apart and become
a part of M60.

621
00:34:45,630 --> 00:34:48,730
In the great game
of galactic warfare,

622
00:34:48,840 --> 00:34:50,700
losing can be catastrophic.

623
00:34:50,800 --> 00:34:53,040
For weak and small galaxies,

624
00:34:53,110 --> 00:34:55,510
resistance is futile.

625
00:34:57,740 --> 00:35:00,550
Pillaged for resource is by
their more powerful opponents,

626
00:35:00,650 --> 00:35:03,350
they slowly become
burnt-out wrecks.

627
00:35:06,020 --> 00:35:11,020
But some peaceful galaxies
face an equally terrible fate.

628
00:35:11,130 --> 00:35:12,930
They starve to death.

629
00:35:24,100 --> 00:35:26,240
Cosmic wars are vicious.

630
00:35:26,340 --> 00:35:29,210
They destroy many galaxies,

631
00:35:29,310 --> 00:35:33,480
but violent conflicts can also
give galaxies new life.

632
00:35:35,380 --> 00:35:36,280
Case in point,

633
00:35:36,380 --> 00:35:40,590
galaxy NGC 4485.

634
00:35:41,720 --> 00:35:44,420
NGC 4485 has a nickname
of the two-faced galaxy,

635
00:35:44,530 --> 00:35:45,760
like the Batman villain,

636
00:35:45,860 --> 00:35:48,630
because it has two
different halves of the galaxy

637
00:35:48,730 --> 00:35:50,100
doing completely
different things.

638
00:35:50,200 --> 00:35:53,170
Half of the galaxy is sort of
old and calm

639
00:35:53,270 --> 00:35:54,530
and relatively quiescent,

640
00:35:54,600 --> 00:35:57,470
whereas half of it appears to
be undergoing a sort of

641
00:35:57,570 --> 00:36:00,440
fireworks display
of new star formation.

642
00:36:01,840 --> 00:36:04,080
Why are new stars only born

643
00:36:04,180 --> 00:36:06,350
in one half of this galaxy?

644
00:36:08,450 --> 00:36:09,750
We found a clue on the edge of

645
00:36:09,850 --> 00:36:14,520
a photo taken by
the Hubble Space Telescope.

646
00:36:14,620 --> 00:36:18,460
It was evidence of an attack
by another galaxy.

647
00:36:18,560 --> 00:36:22,200
We think that another galaxy
passed through it just off

648
00:36:22,300 --> 00:36:24,830
center in a way
that strongly perturbed

649
00:36:24,930 --> 00:36:27,770
the gas on one half
of the galaxy.

650
00:36:29,900 --> 00:36:32,540
The two-faced
galaxy skirmish gave it

651
00:36:32,640 --> 00:36:34,110
a gravitational jolt,

652
00:36:34,210 --> 00:36:37,110
forcing clouds of gas together.

653
00:36:37,210 --> 00:36:40,280
When we think of galaxies,
we think of stars,

654
00:36:40,380 --> 00:36:42,050
and of course,
galaxies are made of stars.

655
00:36:42,150 --> 00:36:44,380
But, of course,
gas is the stuff that

656
00:36:44,480 --> 00:36:45,720
stars are made of.

657
00:36:48,190 --> 00:36:49,890
When two galaxies collide,

658
00:36:49,990 --> 00:36:51,760
the gravitational
duel can trigger

659
00:36:51,890 --> 00:36:54,090
a huge burst of star formation.

660
00:36:58,370 --> 00:37:00,670
You need something
to give a galaxy a push,

661
00:37:00,770 --> 00:37:03,500
and that's exactly what
a galaxy collision does.

662
00:37:03,600 --> 00:37:06,840
And when gas clouds
collide, they compress.

663
00:37:06,940 --> 00:37:10,110
And when they compress,
you get knots in them that can

664
00:37:10,210 --> 00:37:12,710
compress more and form stars.

665
00:37:14,750 --> 00:37:16,550
So you can think of
these collisions as very

666
00:37:16,650 --> 00:37:17,780
violent events,

667
00:37:17,880 --> 00:37:21,190
but ultimately, it can
breathe new life into a galaxy.

668
00:37:21,290 --> 00:37:25,320
But the spoils
of war don't last long.

669
00:37:25,430 --> 00:37:28,460
In the short term,
the victor galaxy can

670
00:37:28,560 --> 00:37:31,960
come out glorious with...
With so many new stars.

671
00:37:32,070 --> 00:37:35,370
But this celebration is
short-lived, because that round

672
00:37:35,470 --> 00:37:41,010
of star formation quickly uses
up the material available.

673
00:37:41,110 --> 00:37:44,140
If a galaxy wants to stay
alive, it has to feed on

674
00:37:44,240 --> 00:37:46,180
other galaxies.

675
00:37:46,280 --> 00:37:50,080
So galaxies constantly
need to raid new targets,

676
00:37:50,180 --> 00:37:52,620
and that raises
an important question.

677
00:37:52,720 --> 00:37:55,550
What happens if there's
a galaxy just alone in space?

678
00:37:55,660 --> 00:37:58,690
Nothing else is colliding with
it, sort of a pacifist galaxy.

679
00:38:00,260 --> 00:38:03,360
The poster child for
these peace-loving galaxies

680
00:38:03,460 --> 00:38:06,230
is NGC 1277.

681
00:38:07,530 --> 00:38:11,340
NGC 1277 is
a very peculiar galaxy.

682
00:38:11,440 --> 00:38:15,940
It's pretty big,
and its stars are extremely old.

683
00:38:16,040 --> 00:38:18,480
It basically hasn't
formed new stars in the last

684
00:38:18,580 --> 00:38:19,980
10 billion years,

685
00:38:20,080 --> 00:38:23,320
so it's kind of the veterans
home of galaxies.

686
00:38:24,380 --> 00:38:26,790
NGC 1277 lives in a rough

687
00:38:26,890 --> 00:38:29,520
part of the cosmos called
the Perseus Cluster.

688
00:38:30,890 --> 00:38:35,030
Thousands of other galaxies
surround NGC 1277,

689
00:38:35,130 --> 00:38:38,200
and they are all
ready for a fight.

690
00:38:38,270 --> 00:38:40,030
So you might ask,
why hasn't it had

691
00:38:40,130 --> 00:38:43,140
encounters with other galaxies
that might rejuvenate it?

692
00:38:44,640 --> 00:38:47,710
The answer,
once again, is gravity.

693
00:38:47,810 --> 00:38:53,250
NGC 1277 sits inside this
massive galaxy cluster

694
00:38:53,350 --> 00:38:54,580
that has a ton of mass,

695
00:38:54,720 --> 00:38:56,920
and if you look at its
position, it's fairly near

696
00:38:57,020 --> 00:38:58,480
the center of the cluster.

697
00:39:00,820 --> 00:39:03,520
The combined gravity
of thousands of galaxies

698
00:39:03,620 --> 00:39:06,130
pulls on NGC 1277,

699
00:39:06,230 --> 00:39:10,530
accelerating it to
two million miles an hour.

700
00:39:13,270 --> 00:39:15,000
And so it has spent the last

701
00:39:15,100 --> 00:39:17,670
few billion years traveling
faster and faster.

702
00:39:17,770 --> 00:39:19,910
Until now, it's almost
at its fastest pace.

703
00:39:22,810 --> 00:39:24,240
It's very hard for gravity

704
00:39:24,340 --> 00:39:26,780
to catch it or catch one of
its neighbors

705
00:39:26,880 --> 00:39:30,750
and bring them together to
merge with each other.

706
00:39:30,850 --> 00:39:34,490
NGC 1277 has no chance of

707
00:39:34,590 --> 00:39:37,590
grabbing new gas
to make new stars.

708
00:39:37,690 --> 00:39:43,300
It's dying. All that has left
are old red stars.

709
00:39:43,400 --> 00:39:46,670
When it comes
to galaxies, red is dead.

710
00:39:46,770 --> 00:39:49,170
No new stars means no big stars,

711
00:39:49,270 --> 00:39:52,940
no blue stars,
just small dim red dwarfs.

712
00:39:57,980 --> 00:40:01,780
Galaxies that don't
fight just fade away.

713
00:40:01,880 --> 00:40:03,480
And at that point,
the history of

714
00:40:03,580 --> 00:40:05,520
the universe becomes
really kind of boring.

715
00:40:05,620 --> 00:40:08,190
All the stars will simply
start to die out.

716
00:40:08,290 --> 00:40:09,760
Eventually,
there will be the last

717
00:40:09,860 --> 00:40:11,360
star formed in the Milky Way,

718
00:40:11,460 --> 00:40:13,890
with no new galaxy bringing
fresh material.

719
00:40:13,990 --> 00:40:17,060
Without galaxy collisions,
the universe dies.

720
00:40:24,240 --> 00:40:27,110
Galactic battles mix things up

721
00:40:27,210 --> 00:40:29,540
and replenish gas supplies,

722
00:40:29,640 --> 00:40:33,550
and our own galaxy
has reaped the benefits.

723
00:40:33,650 --> 00:40:38,420
Our Milky Way Galaxy
fought a massive battle,

724
00:40:38,520 --> 00:40:41,820
but that battle may have been
necessary to build

725
00:40:41,920 --> 00:40:44,920
solar systems like the one
we live in right now.

726
00:40:48,800 --> 00:40:51,400
Clashes with
the Sagittarius Dwarf Galaxy

727
00:40:51,500 --> 00:40:54,530
occurred at the same time
the sun formed.

728
00:40:56,100 --> 00:40:58,340
It's possible
that we owe our very

729
00:40:58,440 --> 00:41:02,810
existence to the collision with
the Sagittarius Dwarf Galaxy.

730
00:41:02,910 --> 00:41:05,710
Maybe the gas
that ultimately gave rise

731
00:41:05,850 --> 00:41:07,780
to the birth of our solar system

732
00:41:07,880 --> 00:41:10,080
once came from
another galaxy entirely.

733
00:41:12,390 --> 00:41:16,360
So galactic wars are
both creative and destructive.

734
00:41:17,660 --> 00:41:21,260
Galaxies are built
from collisions,

735
00:41:21,360 --> 00:41:24,300
galaxies survive
from collisions,

736
00:41:24,400 --> 00:41:29,070
and galaxies can also die
from collisions.

737
00:41:29,170 --> 00:41:31,000
Far from being
destructive events,

738
00:41:31,100 --> 00:41:32,710
colliding galaxies may be
the reason

739
00:41:32,810 --> 00:41:34,140
that you and I are here.

740
00:41:37,140 --> 00:41:39,550
Intergalactic warfare
has revolutionized

741
00:41:39,650 --> 00:41:44,350
our understanding of how
galaxies live and die.

742
00:41:44,450 --> 00:41:47,820
Ultimately, it's these galaxy
mergers that are one of

743
00:41:47,920 --> 00:41:50,190
the great engines
of all structure growth

744
00:41:50,290 --> 00:41:52,020
in the universe.

745
00:41:52,130 --> 00:41:55,260
These collisions
got us to where we are today,

746
00:41:55,360 --> 00:41:58,330
and they're gonna determine
the future of all the universe.

747
00:41:58,380 --> 00:42:02,930
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