All language subtitles for how.the.universe.works.s06e04.death.of.the.milky.way.480p.hdtv.x264.rmteam

The fate of our galaxy
hangs in the balance.

The Milky Way is dying,
and we don't know why.

Our galaxy, like all galaxies,
has a limited life-span.

After that, it's lights out.

The race is on
to find a smoking gun.

It's safe to say right now there
are many ways to kill a galaxy.

It's a cosmic
crime scene investigation.

Is it murder most foul?

Or is it
death by natural causes?

The suspects are lined up.

The interrogation is underway.

It's another example of this big
universe of ours

throwing puzzles at us
that now we have to solve.

What is killing the Milky Way?

Captions by vitac...
www.vitac.com

captions paid for by
discovery communications

Earth.

Our home.

Just one of 100 billion planets

orbiting 400 billion stars

that make up an immense
galactic spiral...

the Milky Way.

Galaxies are where stars form,

and, of course,
planets form around stars,

so the story of the Earth,

of yourself, of the solar system

has everything to do
with the story of the galaxies.

The story of the Milky Way
begins 13.6 billion years ago,

just after the big bang.

It's a time when there are
no planets and no stars...

Just a vast, lumpy soup
of superheated hydrogen gas.

Over millions of years,
the temperature drops,

and gravity compresses
the lumps down, until eventually

the hydrogen molecules fuse
and ignite a star.

In time, billions of stars
burst into life.

And the Milky Way
begins to take shape.

You can think of a galaxy
as sort of like a human being.

When you're young and in your
adolescent stage,

you're vibrant and active.

That's a young galaxy
forming stars in a crazy way,

and it's not
even fully formed yet.

At a certain point,
galaxy reaches middle age,

and a middle-aged galaxy really
is what it's going to be...

It has its shape...

But in the long run, a galaxy
will stop forming stars,

and eventually, just like we
all die, our galaxy will die.

So, at what stage of life
is the Milky Way?

Is it a healthy,
active youngster,

or is it heading
for its deathbed?

Scientists can determine
each galaxy's stage of life

by its color.

So, we see different colors
of galaxies in the universe.

We see galaxies
that are tinted blue

and galaxies
that are tinted red.

When we see a blue galaxy, that
tends to be a younger galaxy

full of bright,
hot, newly formed stars.

When we see a redder galaxy,

that tends
to be a dimmer, older galaxy

that isn't forming new stars
in the present moment.

All its stars are aged
and older and redder,

and so the entire galaxy
casts a different hue.

So, what color is our galaxy?

It's a simple question, but the
answer is hard to come by,

even though we've been looking
at the Milky Way

for thousands of years.

The term "Milky Way" is ancient.

It goes back to a time
when in the dark sky,

people noticed
there was this light band

that actually went
from horizon to horizon,

and that band turned out

to be made of thousands
and thousands of stars

actually too far away
to see individually.

But it took us
a long time to realize

what the shape and the scale
of the Milky Way galaxy is.

The amazing thing to think about
is that we actually don't know

our home galaxy
very well at all.

We actually live in the middle
of this disk of gas and dust,

and that obscures our view of
the larger Milky Way.

Using visible light,
we can't even see to the center,

let alone the other side
of the Milky Way galaxy.

The solution
is to use a form of light

that passes through the gas
and dust...

Infrared.

This is the Sloan
digital sky survey telescope

at the Apache point observatory
in new Mexico.

It's mapping the galaxy
using infrared

and giving scientists
unprecedented insights.

The first sensitive infrared
observations really weren't done

till the last 15 years,

and each of these new windows
on the universe

teach us different things.

In the last 15 years,

Sloan has surveyed
more than 250 million stars,

analyzing their light to work
out the color of the Milky Way.

And what scientists
saw shocked them.

Until very recently,
we thought the Milky Way

was a young, healthy galaxy,

but now there's evidence

that we may be entering
the pathway to death.

The Sloan telescope reveals that
star production in our galaxy

is falling through the floor.

The Milky Way is dying.

And when it stops
forming new stars,

its time will be up.

Paradoxically,
our galaxy still has

star-forming gas in the tank,
so it should be healthy,

but something is killing it off.

So, the Milky Way galaxy
is this wonderful disk

filled with rich hydrogen gas,
lots of dense dust clouds.

It has everything you need there
for star formation,

but it seems to be slowing down
and even turning off,

and right now, we don't really
understand what the culprit is.

With a galaxy killer at large,

scientists embark upon the
biggest murder investigation

in the history of the universe.

Everything in science,
when you're exploring a problem,

is a bit like a crime scene.

You've got the evidence
laid out in front of you...

and we have to
figure out who done it.

Our home in the universe
is dying...

Not the Earth,
but our galaxy, the Milky Way.

It's been producing stars
for billions of years,

but soon, it will stop.

Our own sun formed
about 4 1/2 billion years ago

in the Milky Way galaxy,

and we are not
the oldest star by far.

And yet, tragically,
we actually seem to be

one of the last generations
of new stars in the Milky Way.

Current projections suggest
that in about 4 billion years,

star formation may have
ceased all together,

which is almost just
a blink of an eye

in the life cycle
of the universe.

To find out why, scientists
launch an investigation.

The most crucial question?

How is the may dying?

To kill a galaxy, you have
to get rid of the cold gas,

because that's
what stars form from.

There are many ways
you can do this.

You can blast it out
from the inside.

You can draw it out
from the outside.

You can heat it up
so it's no longer cold.

You can use it all up,

and there's even more ways
you can stop it.

What we have to do is figure out

which way is happening
in our galaxy.

Perhaps the culprit is inside
the Milky Way itself.

A clue comes from
another galaxy entirely.

This is w2246-0526.

Scientists call it a hot,
dust-obscured galaxy,

or "hot dog" for short.

This galaxy is
12 1/2 billion light-years away.

It's the most luminous galaxy
we know of in the universe.

It has the light
of 300 trillion stars.

The source of the intense light
is not its stars,

but a mysterious object
at the galaxy's center.

It's a million times smaller
than the galaxy itself.

There's only one thing
that small and that powerful...

a supermassive black hole.

So, supermassive black holes,
as the name suggests,

are indeed supermassive.

These are billions of times
more massive than our sun.

These are gigantic objects.

The gravity in the supermassive
black hole is off the charts.

It sucks in incredible amounts

of the hot dog's
vital star-forming gas.

And as the gas swirls
to form a disk,

the intense friction superheats
it to millions of degrees

and, in some galaxies,
triggers huge jets.

When a lot of material falls
onto that black hole,

it creates incredibly
energetic jets

that can be tens of thousands
of light-years across.

All of a sudden,
you have this blowtorch

in the middle of the galaxy.

Black hole jets
are bad for galaxies

because they can shut down
star formation.

They can heat gas up,
blow gas out of galaxies,

and they could really kill them.

A supermassive black hole
is cooking the hot dog.

What's going on in our galaxy?

In 2016, scientists at Harvard
discovered damning evidence

that may link the Milky Way's
supermassive black hole

to the galaxy's demise.

Just like the hot dog,

the Milky Way is surrounded by
a vast cloud of blown-out gas,

and the scientists traced
the gas back to its source...

Sagittarius a-star,
our supermassive black hole.

Well, it turns out
our supermassive black hole

had a bit of a hiccup about
6 million years ago.

There's evidence that
some matter must have fallen

into that black hole,
and if it fell in too quickly,

it would have gotten superheated
by its own friction,

and this would have acted,
in a sense, like an explosion.

And that event was huge.

Our galaxy expelled
an incredible amount of gas...

130 billion times
the mass of the Sun.

Large amount of gas.

This event must have been
very catastrophic

for the inner parts
of the galaxy.

Luckily, Earth is in
the outer parts of the galaxy,

where we were able
to survive this event.

Is this the smoking gun?

Is our own supermassive black
hole killing the Milky Way?

The evidence seems to mount up.

But Sagittarius a-star
has an alibi.

It exploded too late.

Sagittarius a-star
got very active,

very explosive
about 6 million years ago,

but that's so recent, it
shouldn't have really affected

the star formation rates.

Something else is going on.

There must be another culprit
besides the black hole.

Studies suggest our supermassive
black hole must have been active

hundreds of millions
of years ago

to stop all star formation
in our galaxy.

Sagittarius a-star
wasn't active at that time,

so it's no longer a suspect.

The hunt is on for
a different galaxy killer,

and scientists are widening
the investigation.

Maybe the killer
isn't inside our galaxy.

It could be that we suffered
a hit-and-run.

It could be that we suffered
a hit-and-run.

Our universe is a crime scene.

Star production in the Milky Way
is breaking down.

Our galaxy is dying,

and astronomers are examining
the body for clues.

The Milky Way's disk is made up
of three sections...

A nucleus, home to the galaxy's
supermassive black hole...

a dense, central bulge
10,000 light-years across,

and the spiral arms...

Full of gas, dust,
and billions of stars.

The spiral arms should be flat,
but they're rippling.

Is this a clue
for the cosmic detectives?

Today, we look at the edge
of the Milky Way,

and we see mysterious
ripples in its gas,

and we wonder,
what's the origin?

Something must have
caused it to happen.

Something like that
just doesn't happen on its own.

The real question is, why?

Whatever caused the ripples
didn't hang around.

Is this evidence of
a galactic hit-and-run?

January 2016.

Astronomers studying data
from the vista telescope

discover something incredible...

three nearby stars.

On their own, nothing special,

except they've recently
left our galaxy,

and they're traveling
at 350,000 miles an hour.

So, we've discovered these stars
that are careening

out of the galaxy
at super-high velocities.

Could these three stars
somehow be responsible

for warping
the Milky Way's disk?

Well, absolutely not.

The Milky Way is so much more
massive than just three stars.

Three stars alone
can't warp a galaxy,

but those three stars can be
indicative of more stars.

They can be indicative
of the presence of, say,

a dwarf galaxy,
and that can warp the galaxy.

Dwarf galaxies are abundant.

But a tiny fraction
of the size of a major galaxy,

like the Milky Way.

So they're difficult to detect.

But these three bright stars
show there's a dwarf galaxy

hiding beyond the edge
of the Milky Way.

And scientists can study
the trio of stars

to rewind the clock

and track back the past
movements of the dwarf galaxy.

Simulations suggest
that millions of years ago,

this dwarf galaxy

punched through the plane
of the Milky Way.

As the fast-moving dwarf galaxy
hurtles towards the Milky Way,

millions of stars seem set
on a collision course.

Catastrophe looks inevitable.

But appearances
can be deceptive.

When galaxies collide, the first
thing you might imagine

is that the stars collide, but
actually, that doesn't happen.

Galaxies are mostly empty space.

If you took the Sun,
which is really big...

It's a million miles across...

And shrunk it down to the size
of a piece of pollen,

the galaxy itself would be twice
the size of the pacific ocean,

and the nearest star to the Sun
would be a mile away.

Those tiny pieces of pollen are
never going to hit each other.

The distances involved
are staggering.

And at the moment of impact,

most of the stars
from the two galaxies

miss each other entirely.

But that doesn't mean
the Milky Way is safe.

Even though the stars
just pass each other,

they do gravitationally
interact as they come close,

and this gravitational
interaction sets them

on a course that is different

than if they were
to live by themselves.

In much the same way
that taking a stone

and dropping it
into a still pond

creates ripples in the water,

a galaxy like this slamming
into the Milky Way

can create ripple effects
throughout the disk.

The ripples in the Milky Way

stretch across tens
of thousands of light-years.

Still, this hit-and-run isn't
enough to kill the Milky Way.

It only causes a flesh wound.

But what if this dwarf galaxy
isn't acting alone?

What if it has accomplices?

There are a lot of
dwarf galaxies out there,

and it turns out collisions
between these dwarf galaxies

and big galaxies, like
the Milky Way, are common.

They happen all the time.

Right now, there are
several dwarf galaxies

that the Milky Way
is swallowing up.

In fact, a really fun thing is
that we're actually closer

to the core of one
of these galaxies...

The Canis Majoris
dwarf galaxy...

Than we are to the core
of the Milky Way.

So some of the stars that you
see around you in the night sky

are actually stars
from a different galaxy.

So, what happens when all these
dwarf galaxies come together

and start pulling and tugging
on a larger galaxy?

Cosmologists believe there could
be hundreds of dwarf galaxies

surrounding the Milky Way.

A collision with just one of
these dwarf galaxies

may have rippled the
Milky Way's spiral arms,

but a gang of dwarf galaxies

could have a far bigger
and far more deadly effect.

Dwarf galaxies and the way
they interact with big galaxies,

like the Milky Way,

can inflect tremendous
change in our universe.

When they slam into a galaxy,
they can change its structure.

The Milky Way would not look
anything like it looks today

without those dwarf galaxies.

Repeated dwarf-galaxy collisions

could have radically altered the
shape of the Milky Way itself.

Their gravitational disruptions
could have created a distinctive

and possibly fatal feature
in the middle of our galaxy...

The galactic bar.

The center of the Milky Way
is elongated.

Instead of it being
shaped like a sphere,

it's more shaped like a bar,
and the bar is made by stars

actually orbiting in this
sort of elongated way.

And this bar can be bad
for the health of the galaxy

because what they do
is help to funnel gas

into the core of the galaxy.

The loss of this gas could be a
way of stopping star formation.

The bar-shaped bulge
at the center of the Milky Way

sweeps our galaxy's
star-building gas

into the galactic nucleus.

Here, it gets gobbled up

by our galaxy's
supermassive black hole.

Without the star-building
material, no new stars can form,

and the galaxy dies.

So, is it case closed?

Are dwarf galaxies
killing the Milky Way?

Is the murder weapon
a galactic bar?

So, it's possible that
the formation of these bars

helps turn off star formation
in the very core of the galaxy,

but that's just the central
regions of the galaxy.

That doesn't explain
what's going farther out

in the spiral arms.

So, if star formation really is
shutting down in the Milky Way,

it's not really
the fault of the bar.

Dwarf galaxies cause the
Milky Way grievous bodily harm

by creating the galactic bar.

But they're off the hook
for attempted galactic murder.

The investigation continues,

and it could be about
to take a dramatic twist.

It might not be that
the galaxy's being murdered.

It could just be
eating itself to death.

It could just be
eating itself to death.

The Milky Way
is being killed off.

And the perpetrator
remains at large.

Scientists
investigating the crime

are running out of suspects.

But the hunt
for clues continues,

so astronomers are examining
the dying body of the Milky Way.

Our galaxy is
a hazy disk of stars

surrounded by a halo
of superheated gas.

It's over 100,000
light-years across.

But it hasn't always
been so big.

When you think about things
so vast,

so gigantic and ancient
as galaxies,

you're kind of tempted to think

that they're
very stable objects,

that they don't change
much over time,

but we now know
that our own galaxy

is the product of many
smaller galaxies

that came together over time,

and there are other galaxies
still colliding with us.

We see galaxies
eating each other all the time.

They collide,
and if one galaxy is very big

and one galaxy is very small,

the little galaxy falls into
the big one, gets torn apart,

and becomes a part
of that bigger galaxy.

The Milky Way might be dying,

but it's still a monster
foraging through the universe,

swallowing smaller
galaxies whole.

It consumes their stars.

But it also has a taste
for their star-building gas.

And it doesn't have
to collide with other galaxies

to feed off of them.

Now, the lifeblood of a galaxy
is hydrogen gas.

That's what actually
creates new stars.

So as a dwarf galaxy
passes by the Milky Way,

the tremendously massive
halo of the Milky Way,

all of that gas, can draw off
material from the dwarf galaxy,

adding it to the Milky Way.

So in this way,
the Milky Way drains away

the lifeblood of other galaxies.

In some sense, you could say
it's a vampire

because a vampire sucks the life
out of other things

so it can remain young.

In its 13 billion-year life,
our vampire galaxy has feasted.

Consuming the lifeblood
of its galactic victims,

the Milky Way has grown fat.

But could this monstrous
feeding frenzy be a factor

in the Milky Way's demise?

Once again, crucial evidence

comes from the
Sloan digital sky survey.

Their telescope maps
the stars in our galaxy,

but it also maps
the galaxies in our universe.

Looking at distant galaxies
is like looking back in time.

Because the farther away
they are,

the longer their light
takes to reach us.

We see the most distant
galaxies not as they are now,

but as they were...
Billions of years ago.

So, when you look
at these galaxies,

you're seeing them as they were
when they were very young,

and you're seeing these galaxies
as they are more recently,

so you can actually look
at the evolution...

How galaxies change over time
as the universe ages.

While studying the data,

scientists make
a dramatic discovery.

They find spiral galaxies,
just like the Milky Way,

dying all over the universe.

And what connects them
is their mass.

There seems to be
an upper weight limit

for the sizes of
spiral galaxies.

Up to about a trillion times
the mass of the Sun,

we see spiral galaxies
that continue to form stars,

but once they pass
this threshold,

galaxies tend to die
and run out of stars.

While devouring
the star-building gas

of smaller galaxies,

the Milky Way
may have grown obese,

and now it could be choking
to death on its own dinner.

But how?

Once a spiral galaxy
is sufficiently big,

it's going to have an
incredible gravitational force,

so any gas that it pulls
to itself

is going to come in
at an incredibly high speed.

That gas is going to be
superheated.

The superheated gas
moves so quickly

that it's prevented
from falling into the Milky Way.

The gas is too energetic for our
galaxy's gravity to pull it in.

Instead, it stays in the halo
around the Milky Way,

and our galaxy's food
supply is choked off.

Eventually, our galaxy
will starve.

This will only happen
if the Milky Way

is over the star-building
weight limit.

But how exactly
do you weigh a galaxy?

One basic way
we can weigh a galaxy

is measure how fast
the stars are moving within it.

So the faster the stars orbit
around the center of the galaxy,

the more massive the galaxy is.

This method of weighing
the Milky Way relies on gravity.

Fast-moving stars need
more gravity to hold them

in their orbits,

and more gravity means
more galactic mass.

When scientists use this
information to run the math,

the horrible truth is revealed.

We've passed
kind of a critical level.

The Milky Way is far too massive
for its own health,

and we've entered
the beginning of the end.

We're running out of gas,
and I mean this literally.

Gas clouds form stars,

and as they form stars,
they're used up,

and so our gas tank
is getting closer and closer

to empty every day.

The investigation into
the killing of the Milky Way

is closed.

The verdict?

The greedy Milky Way
is killing itself.

Over millions of years,
star formation grinds to a halt,

and the galaxy dies.

But could
the galaxy be resurrected?

We seem to be telling
a very sad story.

We're talking about the demise
of the Milky Way galaxy...

The end of star formation...

But maybe it's just
a little bit too soon

to write the death
announcement yet.

Hope could be
just over the horizon.

In space and astrophysics,
really anything is possible.

In space and astrophysics,
really anything is possible.

The shocking case of our
dying galaxy has been solved.

There was no killer.

Turns out, the Milky Way
is eating itself to death.

But is this really the end?

Could salvation
be heading our way?

Even if star formation is
turning off

in the Milky Way now,

we know that it's on
a collision course

with the Andromeda galaxy.

They're moving toward each other

at hundreds of thousands
of miles per hour.

A collision sounds
like something

that's always destructive,

but that's not
necessarily the case.

The Milky Way's collision

with our giant
galactic neighbor Andromeda

won't happen
for another 4 billion years.

By then, star formation
in both of these galaxies

will have stopped completely.

But a giant meet-up
could change all that.

As an isolated galaxy,

the Milky Way is already
in its wind-down phase.

It's not producing as many
new stars as it used to.

But there is one way to generate
a new round of star formation,

and that's through
a galactic merger event.

When Andromeda
gets close enough,

the mutual gravity
between the two galaxies

will start to stretch them out,
pulling them out like Taffy.

Stars will be pulled out into
these long, looping streamers,

and then the galaxies

will physically pass
through each other.

Eventually, the two galaxies
will draw back together again

and merge into
one gigantic galaxy,

and at that point,
all of these gas clouds

will flash into star formation.

As the galaxies merge,
they'll be reborn.

Two dying spiral-shaped galaxies

become a single living
elliptical galaxy

called Milkomeda.

Imagine you're living in
the far future of the galaxy

and you see the night sky

while the Milky Way
and Andromeda are colliding.

It will look like
a very different place.

Rather than one band
across the night sky,

you might have two
as the two disks come together.

It will be a miraculous sight,

but a very, very different
place than we have today.

Our sky will light up for the
first time in billions of years.

Star formation will flare
across the galaxy.

But is it too soon to celebrate?

This new round of star formation

during the merger
of our two galaxies...

While it's very cool
for a little bit,

once it's over, that kind of
sends the new galaxy

into a death spiral.

When new stars are born
in this new galaxy,

many of them are going to
be hot, large, blue stars.

Eventually, those young, hot
stars are going to start to die,

and when they do,
they're going to explode

violently as supernovae.

And those supernovae
are going to start

blasting gas out of the galaxy.

All of the gas is gone.

There's no more stuff
to form stars.

And that's what kills a galaxy.

It'll take
hundreds of millions of years

for Milkomeda
to run out of star-building gas.

And then our new elliptical
galaxy will starve.

But the final blow
is still to come.

Another issue to consider
is what happens

to the two supermassive
black holes

at the cores of
the two galaxies.

Well, initially, they're going
to orbit each other,

stirring up a lot of turbulence,
and they're going to combine.

And because there's
a lot of new, hot, fresh gas,

our new galaxy is
going to be a quasar.

And that quasar is going
to turn up the heat,

it's going to turn up
the turbulence,

and this means star formation
is going to be shut off.

The combined power of the
supermassive black holes

help create a quasar
that tears through the galaxy.

It releases ferocious
beams of radiation

that blast through Milkomeda's
star-forming gas.

It's only just been reborn,

but our newly enlarged galaxy
is once again dying.

Vast galaxies, like Milkomeda,
seem doomed from the start.

Their size creates too many
problems for star formation.

Or... so we thought.

The more galaxies we see,
the more we realize

there's a lot out there
we haven't discovered,

and there's a new class
of galaxies

only recently identified.

These galaxies are more than 10
times the mass of the Milky Way.

And, intriguingly,
they're still forming stars.

Apparently
we've missed something.

Apparently
we've missed something.

4 billion years from now,
the Milky Way is no more.

After colliding with Andromeda,
it's reborn

as a giant elliptical galaxy
called Milkomeda.

Scientists thought galaxies
this big were doomed.

But is hope on the horizon?

The Sloan digital sky survey
has spent a decade

studying
over a million galaxies.

It's discovered a rare
but enormous kind of galaxy...

A super spiral.

These super-spiral galaxies
are spiral galaxies

that are incredibly super,

and by "super," I mean
they have four times the size,

10 times the mass,

and they're weird
because they exceed

the supposed weight limit
for spiral galaxies.

So they shouldn't have
new stars, but they do.

They're very healthy galaxies.

Scientists have found
just 53 super spirals.

Super-spiral galaxies show
that in rare situations,

massive galaxies continue
to produce new stars.

So, is this a lifeline
for Milkomeda?

When we think about
two galaxies colliding,

a lot of our computer models
suggest

that they really
mess each other up.

Things get very chaotic.

But over time, could they settle
back down into a spiral shape?

And, in fact, that may be
what happens with super spirals.

One of the clues is that many
super-spiral galaxies

have double cores.

Instead of there just being
one supermassive black hole,

there are actually
two orbiting each other.

The fact that we see spiral
galaxies with two cores

makes it possible
that you could have a collision

and still survive
as a spiral galaxy.

So maybe there's hope that even
the Milky Way will be a spiral

once it collides with Andromeda.

Picture the scene...
6 billion years in the future.

Milkomeda drifts
through the universe...

not as an elliptical galaxy,
but as a super spiral.

This shape means the galaxy
is far more stable.

The damaging heat and turbulence

generated by Milkomeda's
supermassive black holes

can't disrupt star-building gas
way out in the spiral arms.

Far from dying off,
our galaxy lives on...

Larger than ever before.

But that isn't
the end of the story.

Tens of billions
of years from now,

could the galaxy
continue to grow?

Our local group of galaxies...

Milky Way, Andromeda,
Triangulum...

And then a collection
of dwarf satellite galaxies...

Is gravitationally
bound together,

and eventually,
we're all glued together

into a single massive object.

What does this mean?

This means we might be part of
one of the largest structures

in the universe.

During
its billion years of life,

the Milky Way changes
beyond recognition.

It suffers countless collisions,

feasts on many smaller galaxies,

and gives birth
to innumerable stars.

We talk about
the life cycle of galaxies...

How they're born, how they live
healthy lives making new stars,

and eventually
how they die away.

It's really not
as depressing as that.

Everything in
the universe changes.

Galaxies like ours are in
a constant state of flux.

So when it comes to
the Milky Way,

death really isn't the end.

What we see in our universe

is that there's always
a process of birth and rebirth,

so the future of the Milky Way

is that it's going to
keep on doing what it does.

Galaxies are ever-changing.

10 billion years ago,
the Milky Way

was nothing like
what it is today,

and certainly,
10 billion years in the future,

it'll be a very different place.

Look, I live in this galaxy.

I hope that it can find a way
to rejuvenate itself

through collisions
or some other process

because that gives me some hope

that it'll go on
for a long, long time.