National Geographic Monster of the Milky Way

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,