Nova (1974–…): Season 33, Episode 16 - Monster of the Milky Way - full transcript

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Somewhere not far from Earth,
a star enters its death throes...

and explodes in a violent supernova

Leaving in its wake is
the strangest phenomenon in the cosmos

a black hole.

Our galaxy may be infested
with millions of them.

But now, there's evidence
of something even more ominous...

Black holes -
of unfathomable size and power.

That's a big galaxy and right down
in the centre, we can't see it,

a black hole that's got a mass
of a billion suns.

Astronomers are now studying them
in unprecedented detail...

and finding they are bigger...
stronger... and more destructive
than anyone imagined.



We'd like to think black holes
are far, far away.

But what if there's one
on our cosmic doorstep?

A team from Europe;
and another from the United States

are in a high tech race to be first
to see into the very heart of the galaxy

Now an extraordinary new experiment

is giving astronomers a first
ever glimpse inside a black hole,

to see what's in the lair
of the Monster of the Milky Way.

A new era in astronomy has begun...

High-tech instruments in space

are now revealing a universe
rocked by violent events.

JPL com, Chandra OC...

In the distant galaxies,

astronomers have witnessed
space and time shattered by eruptions

so vast they boggle the mind.



To put this on sort of an Earth scale,

that is equivalent to about a trillion,
trillion trillion atomic explosions.

But what could produce
such awesome power?

Whatever it is, it lives
at the centre of our own Milky Way.

Scientists now believe it is the largest
and most powerful object in the universe

and yet it emits no light.

It is called a Black Hole.

First suggested
by Albert Einstein's equations,

a black hole is space and time
twisted into a furious knot

But the great scientist believed
it could never exist in nature.

Albert never really liked the idea
of black holes, himself.

He thought they were anathema
- this was something
that nature should avoid.

The places where space and time
became infinitely twisted up

he thought no,
nature shouldn't allow that.

Black holes are certainly
odd beasts in the universe.

And they were thought to be peculiar,

so peculiar as to perhaps not even
really exist in the real world.

Simply because your equations show
that they can exist

doesn't require that
the real universe has them.

That there is something
strange and powerful

lurking in the centre of our galaxy
first became clear 75 years ago.

Early radio telescopes recorded
a hiss, like the sound of steam.

As a young astronomer,

Eric Becklin was determined
to get to the bottom
of this mysterious energy source

First, he had to find it.

There was a radio source called
Sagittarius A, a very strong radio source

but there was even debate about
whether that was really the centre or not

Astronomers knew that
the centres of other galaxies
are tightly packed with stars.

But when they tried to see
into the centre of our galaxy,

those stars were obscured
behind a thick veil of dust.

There is so much dust,
between us and the galactic centre,

it is completely opaque.

You do not see
the stars in the galactic centre.

The most powerful telescopes
cannot see it.

Becklin knew that some kinds of light,
invisible to our eyes,

can make it through the dust.

Infrared for example,
travels in slightly longer wavelengths

Infrared radiation gets through the dust

because its wavelengths are longer

and the dust just kind of
rides on the infrared wave.

In the 1960's,

Becklin bought an infrared detector
from a military contractor

and attached it
to the end of a telescope

It was August of 1966.

It was a beautiful night.

As we were looking
with the Infrared detector,

we were seeing more and more stars.

And the signal increased,

and each star gives you more signal.

And we were building up,

as we were getting closer
to the centre, more and more stars,

and we were actually seeing
through the dust for the first time

and then came to a peak -

and then back down again,

and I knew immediately that
that was the centre of our Milky Way

and that I was the first person
to actually see the stars
in the very core of our galaxy.

Eric Becklin had discovered
the very heart of the Milky Way...

the exact location of the mysterious
energy source.

But its staggering power
meant that this was no ordinary star

Scientists believed the only one thing
that could explain the mystery

was the very idea that Einstein had rejected
an object that defies explanation...

What's a black hole?
It's a monstrous, mysterious thing.

It is a point of infinite density.

We don't know how to wrap our brains
around that.

It's a region where space and time
have closed in on itself.

A black hole is a region of space
where the pull of gravity is so immense

that not even light can escape it.

And you reach the point where light
cannot even come out.

And if light can't come out,
you are not coming out.

And if light,
plus you're not coming out,
it is a black hole -

there is no other phrase
we can possibly use to describe it

Welcome to the strange world
of extreme physics...

where space and time
literally cascade into the abyss.

Space itself is falling
inside a black hole.

It's rather like a river
falling over a waterfall

except its space itself
that's falling over the cliff.

It's rather like a kayaker
trying to make their way upstream

on a river that is going too fast.

They get dragged down
to the centre of the black hole.

Gravity becomes a riptide.

The closer you get,
the stronger the current.

Eventually you reach the Event Horizon
- the point of no return.

The matter goes inside the surface
of the black hole

shrinks down to the very centre
where it gets destroyed

in a region of infinite
warped space and time.

And it's gone.

The gravity at your feet
if they're close to the black hole

is a little bit stronger
than the gravity at your head

and you feel that as something
that is tearing you apart.

The tidal forces unrelentingly
getting stronger,

as they exceed the molecular forces
that bind your flesh.

And so you end up
moving through space-time
like toothpaste through a tube.

And ultimately will pull your atoms apart

You will be, as we say,
spaghetti-fied.

As strange as they are,

black holes are a product of the familiar
universe of stars and gravity.

They have their genesis
in a type of enormous star
called a 'Red Super-giant'

It is 10 times heavier than our Sun

yet it will burn itself out
in a fraction of the Sun's lifetime.

Deep inside -

the crush of gravity sends temperatures
roaring above a billion degrees.

Helium and carbon fuse into heavier
elements - oxygen, silicon, sulphur

Then - the star implodes
under its own immense gravity,

sending a shock wave roaring out.

The star digs itself
deeper into space travel

and now goes Supernova
in a violent explosion.

What's left is a dense core
of subatomic particles -

a neutron star -
only about 16 Kilometres across.

It's so dense

that a teaspoonful of neutron star matter
would weigh about a billion tons.

Eventually the gravitational pressure
will be so large

that the neutrons themselves
will be crushed

and there will be nothing left
to stop the collapse.

A black hole is born...

it's a million times
the mass of the Earth,

but compressed so tightly
it literally exits the known universe

Now the effect of that mass
is still in our universe.

The mass is still here in that
it's causing this fold in space,

that goes all the way down.

It has become a hole.

The best way to look at it is

if you stick your finger down
in there, you ain't getting it back.

We know exactly what effect a black hole
is going to have on its environment

on the stars in its vicinity.
On the gas that wanders a little too close

So will we ever see a black hole?

No.

But that's not what's important here.

What's important here is
we can see its paw print.

In search of a black hole's paw print,

Eric Becklin is on a life-long quest
to probe the centre of our galaxy.

The Milky Way is a giant spiraling disc
of over a hundred billion stars.

Our sun is about halfway out,
in the peaceful suburbs.

Becklin is headed to the galaxy's
most exciting and most violent zones.

But to make the final leg of the journey,
he would need help.

So he turned to a rising star
in astronomy.

Andrea Ghez believes that the key
to finding a black hole
at the centre of our galaxy

lies in tracking the stars
that buzz around it.

For about three decades or so

there has been this question
of whether or not

our galaxy harbours a super-massive
black hole at its centre.

And the key to answering
this most definitively

is to watch stars at the centre
of the galaxy orbiting.

Ghez's team set up
at the newly built Keck telescope

on the summit
of Hawaii's Mauna Kea Volcano,

the largest telescope ever built.

Our view to the centre of the galaxy
is absolutely superb.

Our ability to position stars
at the centre of the galaxy

is like somebody in Los Angeles
seeing somebody in New York

be able to move their fingers like this,
okay, just two centimetres.

That is the precision with which
we can measure something that is

twenty-six thousand light years
away from us.

Madeline, we're ready to go.

The conclusive experiment to be done

that really demonstrated
that there was a black hole

was to follow the orbits
of individual stars very, very accurately

and with the highest precision possible

But the stars in the centre
of the galaxy

were not the only thing
Ghez and Becklin had to keep track of

Another group
working in the mountains of Chile

was hot on the same trail,
led by Reinhard Genzel from Germany

This guy here

is a little too dense
to be just a random collection.

We suspected in the galactic centre,

there may be hiding
very massive black holes.

To really be sure
that they are black holes,

we have to go in there
as close as we can.

We can make measurements really good
now to prove it must be a black hole.

Both teams wanted to be the first

to prove that our galaxy
harbours a super-massive black hole,

but Genzel and his team
had a three year head start.

The amazing precision of Keck is the
'ace in the hole' for Ghez and her team

Mark Morris is a veteran
of the Galactic Centre Search.

The German group had already started
to make headway on the galactic centre

even while we decided to pursue this.

We knew that
in a head to head competition,

that as long as they were using
the small 2.2 meter telescope

that they were using compared
with our 10 meter telescope
that we would blow them away.

That bright speck
on the top of this insert.

That's the star which really has given us
the essential clue for the black hole.

It was certainly high excitement,

but on the other hand...
we would have to compile like

at least five years of data
before we could see the stars move

But what kind of cosmic monster
was pulling the stars along?

This is our road map,

and that's the centre of our galaxy

So, there's a large cluster of stars that
are orbiting the centre of our galaxy

Basically the way this experiment
works is you take an image,

you see where all the stars are

and then you come back some time later,
and you take another image.

And you look to see if they have moved

And so the second time we took
an image we knew we were golden

that those stars had clearly moved.

The first order of business
was to see how large the object is,

to weigh it by measuring its gravity.

So we have the black hole here.

The more massive it is,
the more pull there is.

The more pull there is, as it gets closer
to the black hole, the faster it goes.

And we are measuring the speed
of these stars.

That's the key to getting the mass
is measuring the speed of those stars

Andrea's more advanced telescope
made the difference.

The object weighed in at a staggering
3 million times that of our sun.

But that didn't prove
it's a black hole...

It could still be a cluster
of smaller objects.

For the Germans, it was time
to even the playing field.

The VLT, Very Large Telescope,
opened its doors on a mountain in Chile

Both the VLT and Keck were upgraded
with revolutionary technology.

For years, the teams relied on computers

to pinpoint the location of stars
through the turbulence of our atmosphere

Now they could cancel it out with
a new system known as Adaptive Optics

It uses a powerful laser beam
to read the turbulence.

Telescope operators
can use those readings

to sharpen the image
of distant stars and galaxies.

So this little animation shows you
the benefit of adaptive optics.

So you see the stars
without adaptive optics,

you turn the adaptive optics on,
and all of a sudden, you see stars

And in particular, you see stars
near the centre of the galaxy,

we track all of them,
but these are the ones that
are the key to the problem.

These new eyes
were delivered just in time...

With both teams watching,

one of the stars made a dramatic
hairpin turn around the centre.

In 2002,
it made a huge jump to over here

So, whoop, all the way around.

The star was initially going very slowly
and then moving around very quickly

and at that point coming very, very,
close to the central black hole.

It is moving on order
ten million miles per hour.

So it is just speeding away.

The star had come close enough
for the teams to see

that it had to be
circling a single massive object.

All other physical explanations
of what was at the very centre were gone

The only thing left was a black hole.

To astronomers around the world,
the evidence was impressive.

I have to say when I first saw
Andrea's video I was stunned,

when I saw that star come out
of the left side of the frame

and go zipping around

and go shooting off
into the other end of the frame

and it move around a point in space
and nothing was there.

That we could with our instruments,
together with our minds,

effectively travel
to the centre of the galaxy,

26 thousand light years away,

and collect the evidence for such an
incredible object was really
an amazing achievement.

The European and American teams

had confirmed that a black hole
was there without actually seeing it

From our quiet corner at the far edge
of our galaxy's spiral,

it's hard to imagine
the violence at its centre.

The closer you draw toward the centre,
the denser it gets.

Our destination: the galaxy's
central hub, brimming with stars

known simply as "the Bulge"

Venture into the bulge
and you enter a busy highway.

It's jammed with star traffic
speeding in every direction

and it's always rush hour.

There is a lot of gas.

There is a lot of dust.

This is absolutely
the most crowded place in our galaxy

There will be stars all around us.
An incredible density of stars...

you couldn't exist there;
there is lots of ultra violet radiation

X rays are floating around.

Gas clouds bash into each other...

So it is
a very hostile environment really.

The black hole is surrounded by a cloud
of super-hot gas that's falling in.

The space around the black hole
is so warped -

it distorts the light
that scatters across it.

As bizarre as it seems,

the gravity of a super-massive
black hole is so spread out

that you might fall in
and survive... for a moment.

During the final descent,

you would then go into the event horizon
but you would actually not feel it

because you are a small body,
compared to the large massive black hole

Now, thanks to a computer simulation,

based on Einstein's own equations -
we can visualize the scene.

As you move toward the black hole's core

you hit an inner horizon,
a log jam of trapped light and energy

At a certain moment
as we hit the inner horizon,

there is this infinitely bright
blinding flash of light.

That is the stuff that has been
waiting there trying to get out,

it is just held there
at the inner horizon

it would vaporize you.

Almost certainly
if you fell into a real black hole,

you would simply, unfortunately die

But that's not the end of the journey

The computer storm can be turned off,

and the strange predictions of
Einstein's equations allowed to play out

A passageway opens up -

a tunnel through space and time
known as a wormhole.

We now leave through a strange door
known as a white hole.

Here the twisted logic of extreme
gravity goes into reverse.

Instead of being sucked in,

you'd be catapulted out
to the far reaches of time and space.

But to where?

In science fiction, wormholes offer
handy escape routes to other universes

In reality, the inside of a black hole

is probably too chaotic and violent
for a wormhole ever to form.

The black hole
at the centre of the Milky Way
is strange enough as it is.

But is it the norm,
or is our galaxy a freak of nature?

To find out, astronomers have mounted
a major international project

to search galaxies
throughout the universe for evidence
of super-massive black holes.

From Apache Point in New Mexico,

astronomers are probing big galaxies
out to a billion light years from Earth

They take a series of steel plates

and drill holes to exactly match
the location of galaxies in the night sky

Then they plug fibre optic sensors
into those holes,

and for the first time ever,

they can use the plates
to capture the light
of hundreds of galaxies per night

The astronomers are looking for
a distinctive light signature
coming from a galaxy's core.

It's a sign of hot gas
swirling into a black hole.

The goal of the project,
called the Sloan Digital Sky Survey,

is to map a quarter
of the entire Northern sky,

to find out what kind of galaxies
make up our universe

and how they are arranged.

Of the 125 billion galaxies
that make up the visible universe,

more than a million
have so far been analyzed.

Nearly all the large ones,
circled in red,

bear the signature
of a super-massive black hole.

The closer we look
to the centres of galaxies,

the more we find these black holes,
and the inventory is rising high.

So any idea for the formation
of a galaxy

will now have to include
some explanation for how you get
a black hole in its centre.

But how did every big galaxy
in the universe

end up with a giant black hole
in the middle?

To understand,
go back to the very beginning...

the Big Bang.

Matter and energy rush outward
as the universe expands.

You have the big bang handing you
your birth ingredients,

your hydrogen, your helium,
your traces of some other elements

So it is kind of like this soup.

You put it together and stir it.

It's gravity that stirs the soup.

Over billions of years

it moulds the universe
into a spider's web of gas and galaxies

Within this web gravity draws together
wisps of hot primordial gas.

Over tens of millions of years,
the clouds of hydrogen gas coalesce,

growing more and more dense.

Some grow hot enough to ignite.

The first stars are born...

giants, hundreds of times
bigger than our Sun.

They burn out quickly
and explode in the flash of a supernova

Billions of years later,

an orbiting satellite
called Swift is in position
to capture that flash of light.

Swift is the eyes
of an international group of astronomers

Within 30 seconds of detecting a flash,

it sends out an alert
via mobile phones, pagers, and emails

The astronomers scramble
to their telescopes.

Speed is vital.

They have to catch the light beam

if they are to probe the dark secrets
behind these distant disasters.

First they determine
how far it has travelled,

give it a name
and pinpoint its birth galaxy

By analyzing the light,

they have gleaned the distinctive
signatures of black holes being born

The most distant are the earliest
generation of primordial monsters.

We could be forming the seed
of the super-massive Black Holes

that we see galaxies today,

very early on when the very first
objects forming the universe.

We can now with our big telescopes
look back in time.

And sure enough what we find is
that at the same time
when the galaxies formed

also the black holes formed...

it may very well be
that they needed each other.

This computer simulation shows
how our Milky Way galaxy was born

It grew over billions of years

from a swarm of smaller galaxies,
smashing together, merging.

In a cosmic dance of death,

the infant galaxies swirl around
and orbit one another,

gravity pulling them closer.

If another galaxy comes too close

they will each feel each other's gravity

What started out as a stately ballet
of stellar orbits,

moving around the centre of their galaxy,
has now become this maelstrom.

There is no other way to say it:
galactic cannibalism.

That is what they are doing.

They are dining on their neighbours,
eating entire galaxies.

Well for every galaxy you eat,

if that galaxy has a black hole in its
centre it is going to eat the black hole

And the black hole will work its way
down to the centre of the large galaxy

making the centre of the galaxy bigger,
as well as the galaxy itself.

As galaxies swallow each other,

the black holes at their centres
merge and grow.

There was an epoch once
about one two three billion years
after the Big Bang

when in fact galaxies were forming
or at least they were tremendously
more active than now

And at the same time black holes
already existed, had formed,

and were feeding at tremendous rates,

producing very powerful quasars.

Quasars are bright beacons of light
at the centres of distant galaxies,

where feeding black holes shine brighter
than anything else in the universe.

The Hubble Space Telescope
peered into a dormant quasar

in a nearby galaxy called M87.

It found a tiny central region
where gas is heated
to tens of millions of degrees

and whipped by gravity
to millions of kilometres per hour.

So what had become obvious was that

there was a tremendous amount of mass
and a very small volume,

but that mass
was very unlikely to be stars

like those that we see in our galaxy.

Astronomer Brian McNamara believes
giant ravenous black holes

can have a profound effect
on the surrounding galaxy and beyond

Can we get an offset?

180.
180, 180, same direction.

We are setting at 360, 360.

The guider is locked up.

McNamara is studying a trail
of devastation left in their wake.

It's not amazing.

All of these other galaxies
are gravitationally bound
to this galaxy cluster.

So they're all buzzing around this giant
galaxy like bees buzzing around a hive

These clusters are the product of
galactic cannibalism on a cosmic scale

This computer simulation shows
how a galaxy cluster evolves

in a dense region of the universe,

tens of millions of light years across

Hundreds of galaxies form
then swarm toward a common centre.

A central galaxy swallows them up.

As it grows,
so does the black hole.

McNamara is searching
for the monster's paw print.

So that's a giant galaxy sitting
in the middle of a cluster galaxies

And so the idea is that's a big galaxy
and right down in the centre
you can't see it

and we think there's probably
a black hole that's got a mass
that approaches a billion suns.

It very recently in the last several
tens of millions of years
gobbled up a lot of matter

and it caused a huge eruption.

McNamara zeros in on a distant galaxy
cluster 2.5 billion light years away

Called MS07, it's hidden
in a vast cloud of hot gas.

There is an atmosphere of gas
that pervades the entire galaxy cluster

And it is an atmosphere
like our atmosphere except that
it is far less dense

and it is it is much much hotter.

McNamara noticed
that two immense cavities in this cloud

had been hollowed out.

So between this cavity here
and that cavity there,

we could stuff
600 Milky Ways in there.

It's just astonishing.

The energy involved is huge.

McNamara believes this eruption of energy

is the most powerful
since the big bang itself.

He traces its source to the core
of the giant central galaxy,

a super-massive black hole.

But how does a black hole,

a creature famous for devouring
everything within its grasp,

spew energy across the universe?

As matter falls in

what we know now
is that it spirals around in a disk,

ok very much the way when water
goes down the drain.

And the speeds that matter
can achieve around that black hole

approach the speed of light.

And when matter travels at that speed

it gets a tremendous amount
of energy.

Matter falling into a black hole

is a lot of stuff trying to get into
a very small place.

And so it is like trying to fill
a dog dish with a fire hose.

Most isn't going to get in.

A high-speed whirlpool of matter
coils around the black hole,

creating a powerful magnetic field

that hurls enormous volumes
of gas outward.

It produces a powerful jet of matter-

hundreds of millions of times
the power of the Sun-

that blasts right out of the galaxy.

There is no question that black holes
at the centres of galaxies

have a profound influence
on their surrounding,

they send out these huge jets,
moving at almost the speed of light,

and those jets can send shock waves
into the surrounding medium,

change their surroundings completely.

They have a dramatic influence.

These jets can literally
sterilize the galaxy,

by halting the formation of new stars

In principle galaxies can grow
to very, very large sizes

and what we see in the universe
is that they don't.

And we think that the supermassive black
holes at the centre may be the culprit.

They may be responsible for
preventing runaway growth of galaxies

In smaller galaxies,

all this violence
can have a creative impact.

Black hole blast waves
spread heavy elements generated
in the core of the galaxy,

setting the stage for the formation
of new solar systems.

We usually think of black holes
as god's dumpster,

but they really are actors
on the galactic stage.

The Monster of the Milky Way
may have helped create our solar system

but what's to stop it from wiping us out?

It all depends on the Monster's diet.

One of the key differences between
galaxies with super-massive black holes

is whether or not the black holes
are lit up,

because they are basically binging on
a lot of material in its surroundings

For years, our own black hole
has probably been fasting.

But in 1999, the Chandra Space Telescope

detected a powerful signal
from the galactic centre.

Station 34, Chandra OC.

Just to let you know we have about
18 minutes remaining at the playback

An explosion
just outside the Event Horizon...

For the Galactic Centre teams,
the blast is a wakeup call.

It was a hot piece of news at the time

A remarkable fact for all of us was
for many years

how inactive the black hole was.

The big puzzle is there are
so many blue stars that side and...

Now, both Reinhardt Genzel
and Andrea Ghez

race to their telescopes.

They will try to see whether
the black hole's about to binge.

The two teams join in a worldwide effort

Five major observatories
will probe the black hole.

From space, the Chandra X-ray Observatory

will watch for high-energy light.

Reinhard Genzel heads to Europe's
Very Large Telescope

set in the high desert of Chile.

Andrea Ghez climbs
Hawaii's Mauna Kea volcano,

to the legendary Keck Observatory.

When you are there
it is an incredible rush,

I mean you are very much on
for the few nights

that you are there,
hoping that that your experiment works

Hoping that the weather cooperates.

Telescope time is precious,
there's no room for mistakes.

Madeline, we're ready to go.

The teams have five short nights
to find out how much
the black hole is eating

by measuring the energy that flares out

Night one - the Chandra headquarters
in Cambridge Massachusetts.

Zoom in a little more.

Alright, so, first night, it doesn't
look like there are any flares.

The telescope turns up only noise,

x-ray flashes from small black holes
roaming through the galactic centre

Four more chances, guys.

Night two -
the telescope in Chile has problems.

Can I see the monitor the correction?

There's still not very much there.

Well we do need to sacrifice now someone
to the gods or something like this.

Should I volunteer?

Even if there are flares,

the Very Large Telescope can't see them

We have to redo the acquisition.

The correction was unstable.

A patch of humidity
is warping the delicate optics

everything's a blur.

Look at the guide star.

Alright now we have a problem
with the main mirror,

the eight meter mirror,
seems to be deformed.

In Hawaii, it's not much better.

The Galactic Centre is playing
hide and seek behind overcast skies.

We're fighting with clouds.

It looked better just a moment ago.

It looked like we were just ready to go
But now it's looking like.

Finally on night three.

Look at this, it's really flaring.

The German team's luck changes...
in Chile they spot an outburst.

That's the best flare event
that we saw in this run.

A new point of light appears in the star
field - one that wasn't there before.

Here clearly we see there's basically
no source at that position.

Just those two blobs.

On the other side in the same region,

and we clearly see those same two sources

And now in between
we see an additional source.

So this is the flaring stage...

When the Chandra team
receive their data from space -

they can see it too.

Oh! Alright... Here we go.

Oh, yeah, that's huge...

It's a least a factor of 15 or so.

The x-rays show a spike

that coincides with the flash of light
captured by the Germans.

News from our colleagues.

Of course telling us
they are a few hours further west,

so the sun hasn't even set yet.

The stars of the Galactic Centre haven't
yet risen above the Hawaiian horizon

Ghez has missed the flare.

This part kills me, waiting.

But the next night
the team gets what it's looking for

Well I like that image a whole lot better

This is it! Really? Yeah!
Really!

We were taking measurements

and you didn't see anything
from the black hole,

all you saw was a star
and then bam it was there.

And bright.
And fifteen minutes later, it was gone

So that was our moment
to make the measurement

and it was extremely exciting to know
that we had actually been able to catch it

One day, not long from now,

these scientists hope to see
the monster directly...

by linking observatories
around the world

in a giant telescope powerful enough
to peer deep into the centre of the galaxy

What they will see is a dark spectre
framed by flashes of light.

These are just flares compared with
the monumental eruptions of its past.

Our black hole had a wild teenage life,
I am pretty sure of that.

It probably had jets.
It threw lots of matter out.

It had a grand old time.

And now it has decayed
into the Old Folks Home of the galaxy.

But what would it take for
the Monster of the Milky Way to awaken?

Could explosive jets of energy
once again blast across our galaxy?

The watch is on
at the very ends of the Earth.

Astronomers have come to the South Pole

to monitor radio signals
from the Galactic centre.

They can see signs of a disaster
in the making.

A vast ring of gas is looming just beyond
the Milky Way's central black hole.

In time, it will accumulate
300 million Suns' worth.

When the ring reaches a tipping point,

it will begin to funnel into a second ring
that orbits close to the centre.

The inner ring will condense
into a giant cloud.

Within it a storm of new stars
will be born.

Then the gas cloud
will begin to spiral down
into the grasp of the black hole.

When the feasting starts,

the eruption will be visible
far beyond our galaxy.

Our galaxy will survive
its black hole's upcoming feast.

But it isn't likely to survive
a threat further down the road...

Galactic Cannibalism.

Our galaxy, the Milky Way,

is not immune from these colliding
galaxy scenarios.

We've got neighbours.

We are falling towards each other.

And one day we will collide.

Even now, the end of our galaxy
is approaching.

Our giant neighbour, the Andromeda Galaxy,
is charging toward us.

Knowing the galaxies' dimensions,
flight paths and the laws of gravity,

scientists can predict
how the clash of titans will unfold.

What our simulations show
is what could happen

basically in quite a few billion years
from now,

when the two galaxies will actually
approach each other and merge.

First the galaxies will circle
and entwine, ripping each other apart.

Imagine what that might look like
from another galaxy.

They will see two grand, beautiful,
spiral galaxies moving towards each other

slowly losing their shape.

They'll see new avenues
where stars and gas

can funnel down
towards this newly formed centre.

Feeding this reborn monster.

The collision will send
a blizzard of stars and gas

billions of kilometres into space.

Some will shoot toward
the crowded core of the new galaxy,

spurring even more massive explosions.

Amid the turmoil, our little solar system
will be flung into the voids of space,

or driven into the black hole's jaws.

In the process of merging there will be
a very strong star burst event,

occurring at the time of the merger,

as all of the gases being funnelled
and towards the centre.

As well as the two black holes
that are likely to merge

will also swallow a lot of this gas.

So the black hole in our Milky Way
will ignite emitting so much energy

that all of the gas around
it will again be blown away

in this very substantial wind,
and very substantial outflow.

The Milky Way will be destroyed...

but what about the black hole
at the centre?

It will merge with Andromeda's.

Stars and galaxies may come and go,

but super-massive black holes
just keep getting bigger.

Once considered freaks of the cosmos,

black holes may simply be the workings
of a restless universe.

As we forge ahead in trying
to understand how we came into being,

and how all of the matter
got put down in the universe,

we can't leave
black holes out of the picture

because it seems they play a fundamental
role on very, very large scales.

Black holes not only actively shape
the landscape in which they are invented,

they wreak havoc upon it.

You throw in a hungry beast
in the middle of it all

and it distorts the gas clouds.
It flings stars hither and yon.

It creates energy fields that would fry
any life in its vicinity.

That kind of makes the centre
of galaxies interesting places.

So, black holes
are kind of the spice of the universe.

They are a major player

in the evolution of the things
that light up our night sky.

Even though we can't see them,

they are in a sense the secret shadows
behind the waltz of the galaxies.

Scientists today are bringing us
closer to a shadowy presence

that long ago erupted across our galaxy

and shaped the universe we know.

For the moment the monster
is resting quietly...

but how long will we have to wait
for it to rise again?