Swallowed by a Black Hole Horizon

Nothing is more seductive than the unknown.

Nothing more compelling than a place of danger

that lies beyond normal comprehension.

Of all those places,

perhaps the strangest of all

are black holes.

They are an exit point from the universe.

Hidden trap doors in the fabric of space-time.

What would it be like to enter the void

and succumb to a black hole's dark mysteries?

Now, for the first time,

astronomers are set to find out.

For the first time, the black hole at the centre of our very own galaxy

is about to yield up its secrets.

High above your head in the centre of our Milky Way Galaxy

a violent drama is about to unfold.

Our supermassive black hole is getting ready to have dinner,

as a gas cloud three times the size of the Earth

is caught in its gravitational hold.

Across the world astronomers are getting ready to discover

what happens when a black hole gets ready to feed.

If you could see how something falls into a black hole,

that would be something we can see for the very first time ever,

that we see how a black hole starts getting fat.

That would really be fantastic

if we, if we can witness that in front of our eyes.

For astronomers, this year's event is the first time in history

it will be possible to witness and record the workings

of one of these great gravitational engines.

Some of the excitement

is just childish pleasure

in seeing something violent about to happen, and anticipating it.

Scientifically it's very interesting because it's really unprecedented.

This is the first time really in human history

that we have not only known an event like this was going to happen

but that we are prepared with the right sort of technology

to see the details unfold.

There's nothing anywhere near as extreme as a black hole.

The disturbing truth about black holes

is that they're a boundary between the known universe

and a place that will forever lie beyond the reach of science.

They are an anomaly of gravity so strange,

it is barely possible to comprehend.

Black holes represent

the regions where our current theories of physics completely fail.

What actually happens there, we don't know,

so it's this very weird situation

where our understanding kind of predicts its own failure.

What gravity tells us

is that everything at the centre of a black hole

should get smashed together in a region

smaller than even a proton or an electron

or any kind of regular part of matter.

If you were to fall inside what we call the radius of the black hole,

the event horizon, then nothing could get out of that region.

Once it's gone, it's gone for ever.

The great dream for astronomers

is to see those final moments

as it falls over the edge into oblivion.

The kind of ideal situation that we're aiming for

is to really be able to see what happens

very close to the event horizon of a black hole.

This is not something we can do in a laboratory on Earth,

so the only hope

is to use observations of black holes in the universe

to actually see what's happening,

and that is kind of the Holy Grail

of astronomical observations of black holes.

But if watching matter tumble over the edge of a black hole

might now be possible,

it is only because of the efforts of a generation of astronomers

to wrestle these dark dragons of the cosmos

into the realms of scientific reality.

As is often the case, it began with a series of observations

that made no sense to anyone.

A new generation of radio telescopes had come on stream in the 1950s

that made it possible to see the universe

in a completely different way.

Almost immediately they began to detect a series of strange,

previously unseen, sources of light.

Nothing had ever been seen like them.

These things looked very different, very strange,

much more powerful, much larger and really different

than sorts of galaxies and stars in our neighbourhood.

But that was not the only surprise.

People began to realise that these tiny star-like things,

or they looked like stars,

were actually putting out as much energy as a hundred galaxies

and yet they didn't look like a galaxy at all.

The paradox was how something so small could be so bright.

What could possibly produce such a mind-boggling source of power,

with some of them pumping out more energy than a trillion suns?

They were given the name quasars.

Quasars became a very big and deep mystery

because they were distant in the universe

and therefore we were seeing the universe

as it was billions of years ago

and they were more potent, more luminous

than anything else that we'd come across before.

Solving that mystery turned out to be the crucial step on the journey

that would eventually lead to us observing the strange behaviour

of our own feeding black hole.

So that's twice times Newton's constant,

onto the mass of the black hole

and if you divide...

What was first needed was a maverick insight

from one of modern science's truly original thinkers.

I was thinking about that mystery, that's absolutely true,

and there were a number of different ideas that were put forward

but none of them was terribly convincing.

The mystery of what could account for the quasars' extraordinary brightness

was THE hot topic in astronomy during the 1960s,

as astronomers began to grapple with the new enigmatic objects

that had been found by the radio telescopes.

One astronomer keen to have a crack at the problem

was a young researcher called Donald Lynden-Bell.

The sky looked totally different

in the radio than it looked in the optical,

and that was a big problem,

and the question was, what were these things?

While his colleagues were staring down telescopes,

Lynden-Bell approached the problem through theory.

He wanted to find out how something as small as a quasar

could possibly be so bright.

This had an enormous quantity of energy coming out of it,

and it came from a very small size.

Now, putting those numbers together,

one could already see

the mass of the energy required to give the emission

was, like, ten million times the mass of the sun.

But the problem was that quasars are tiny in size,

with nothing like the scale of ten million suns.

Lynden-Bell realised that there was only one thing

that could possibly be so small yet have so much mass,

those mathematical anomalies conjured up by theorists

that had been predicted but never observed:

supermassive black holes.

It suggested a baffling paradox,

that quasars are really shining black holes

capable of emitting the energy of entire galaxies.

But Lynden-Bell then went further.

I predicted that there would be these massive objects

found in the nearby galaxies.

He brought his ideas together with a bold conceptual leap

about where these supermassive black holes would be found in the cosmos.

Typically a large galaxy would have a black hole,

the sort of amount of many millions of solar masses, in mass.

And that these would typically reside in the middles of large galaxies.

It was a pretty bold prediction.

Yeah, well, I come from a military family!

Lynden-Bell's hypothesis was so radical it seemed far-fetched.

Inside the centre of every large galaxy in the universe

lurks a supermassive black hole.

If Lynden-Bell was right

and every galaxy has a supermassive black hole at its centre,

then there should be one right in our own back yard,

in the middle of the hundreds of billions of stars

that form our own galaxy, the Milky Way.

The problem was trying to map our galaxy from the outside

when we can only view it from within.

Seeing round that obstacle

would take ingenuity and some careful observations.

One of the problems of living inside a galaxy like the Milky Way

is that because we're inside it,

it's really difficult for us to see what shape it is,

how big it is, and where in it we actually live.

But if you look carefully

the stars aren't spread smoothly across the whole sky.

They're gathered together

into a band that loops around the sky which we call the Milky Way.

That bright strip across the sky,

with its extraordinary abundance of stars and clusters,

was a clue to the nature of our galaxy.

It was obvious to astronomers for quite a long time

that most of the stars were gathered together into a flat layer or disc,

and that we were within that disc.

But we still don't know whereabouts in the galaxy we are.

And then in the early 20th century,

an American astronomer called Harlow Shapley

hit on a way of trying to find out

where the centre of the galaxy might be.

He used objects called globular clusters

which are actually found all over the sky.

Bright sources containing thousands of stars,

globular clusters,

are spread out in a sphere around the Milky Way's central disc.

Shapley realised they were in effect signposts

to where the centre of the galaxy could be found.

He plotted where the clusters were

and he found that although they were spread all over the sky,

they were concentrated in a particular direction.

And that told us that we weren't at the centre of the galaxy,

but the centre of the galaxy was in this direction here.

So at last

astronomers knew exactly where the centre of the galaxy was,

and they also knew pretty much how far away it was.

At last astronomers had a map of our galaxy.

A panorama of the Milky Way

it would never be possible to see from planet Earth.

27,000 light years from our solar system is the centre of our galaxy.

If we were ever going to have a chance

of seeing a black hole at close range,

according to theory, it should be hiding right here.

Theory is one thing but astronomers work by observation and proof.

That would mean actually finding the black hole and seeing it at work.

The good news is that there should be a supermassive black hole

somewhere at the centre of the Milky Way Galaxy.

It's not that far from us and we know exactly where to look.

We know where to point our telescopes.

The bad news is that the centre of our galaxy

is an incredibly crowded and busy place.

Many, many stars... Stars are packed much more densely

than they are where we live in the Milky Way Galaxy.

It's this incredibly confusing and noisy environment.

The stars around the centre of the Milky Way

are hundreds of times denser than they are

in the region around our sun.

Finding an invisible black hole in all that swirling chaos

would not be easy.

It's like trying to pick out an individual

inside the middle of a busy city

where there are lights and cars

and things happening all around them.

But that wasn't the only problem.

Vast swirling clouds of dust and gas prevent visible light

from the centre of our galaxy from reaching us,

making what lies beyond hidden from view.

It's like putting a blanket over the thing you're trying to look at.

It's putting a thick fog around that

and so there's only certain wavelengths of light

that can penetrate through that.

Without the means to see through that dust,

the black hole that theory suggested

should reside at the centre of our Milky Way

would remain nothing more than a bold but unproven idea.

With the quest to find the black hole seemingly blocked,

there was nevertheless one glimmer of hope.

Now at least astronomers had some sort of notion

where one should be hiding.

To tackle the problem, what would be needed

was a new generation of telescopes

and that would take a new generation of astronomers.

We were just at the point where we had the technology

to address that question and so

in some sense it was,

I had the right hammer and I was looking for the right nail.

With her Los Angeles group, Andrea Ghez

began work on a telescope

that could see through to the hidden centre of our galaxy.

Just as I arrived at UCLA with my first faculty position,

everything was falling into place in terms of the ability

to answer this question at the centre of our galaxy.

The telescopes were getting bigger

so you had the ability to see fine details.

We had an explosion in infra-red technology

which meant that we could detect the kind of light that the stars emit,

that you could actually see here on Earth and get through a lot of dust.

The challenge was developing a telescope

capable of overcoming the blurring effects of the Earth's atmosphere.

Using lasers and specially-developed software,

Ghez developed a telescope

that made constant adjustments to tune out atmospheric distortion.

We had a huge amount of scepticism.

No-one had ever done this,

but as I told my students, never take no for an answer

so you find somebody that will help you out,

loan you some telescope time and let you do a proof of concept

to show that yes, this technology will work,

and it's freshman physics that tells you that if the technology works,

you should be able to see something if there is indeed a black hole.

With her new telescope, the final obstacle

to seeing into the centre of our galaxy had been removed.

It was now possible to see in unprecedented detail

right into the area where the black hole was believed to be hiding.

If there is a black hole at the centre of our galaxy,

that's going to force these objects

that are really close to the black hole

to move much faster than they would move if there were no black hole,

so the first thing you want to see

is that there are very fast moving objects

where you think the black hole is.

So, with our pictures that we took,

what you can measure is how these stars move on the plane of the sky.

You take one picture,

you come back a year later,

you take another picture and you see where they have moved to

and what we see in this box

are that there are stars that are moving incredibly quickly.

That was the first evidence for the black hole.

Once everything had been plotted out,

this is the map of the galactic centre they were able to produce.

It showed that stars were hurtling around in very fast and tight orbits

but what Ghez was interested in was what they were circling around.

If there's a black hole,

there is a further prediction you can make

about what these stars are going to do.

They are going to move around the black hole on very short periods.

In other words you're going to be able to see them

move on more than just straight lines.

As part of their travel around the black hole,

these stars are going to move around the black hole

because of the gravity just like planets move around the sun.

There's only one thing that has the sheer force of gravity

to compel such huge stars to veer round on such tight trajectories.

So what we see is that indeed you can see these stars whip around.

In fact from these images

you can actually tell where the black hole is.

The black hole is at the centre of the focus of these orbits.

It was a stunning discovery.

After a quest lasting decades,

Donald Lynden-Bell had been proved right.

Here indeed, just where he had predicted,

was a supermassive black hole.

But in the last year, the quest to find and understand black holes

has suddenly become even more exciting.

That's because out there in space

something is about to happen

that really is going to drag black holes out of the shadows

to reveal them as they really are.

The reason for the excitement

is all because of a discovery made in Munich.

Here a group working with the European Space Observatory

had shared credit for discovering the black hole

at the heart of the Milky Way.

In late 2011, they made an almost accidental discovery,

a discovery that's triggered this year's rush of excitement.

It was while reviewing some data

which had previously been dismissed as second rate

that they noticed something unusual.

We decided in 2011

we should look at our data which is B-rated, so to say,

data which is of somewhat lower quality because the resolution

is not as good as you would get it under the best weather conditions.

And then, boom, there was all of a sudden one source

which was very close to the black hole.

The object didn't appear to have the profile of a star.

Instead it seemed to be a gas cloud

moving at huge speeds right in the direction of the black hole.

But what really rang alarm bells was the way it had changed shape.

We see that this gas cloud as it moves

closer and closer to the black hole is getting spaghetti-fied,

like you see it in school books,

according to the tidal shear, as we say,

the tidal disruption by the black hole.

It was moving quite fast

and it's not moving in a straight line but it's a curved line,

and that's a very, very bad sign

because it tells you, well, there's something acting on it.

It tells you, well, gravity is pulling on that object.

It's pretty much directly head-on

moving towards the centre of gravity, the black hole.

The team's observations suggest the object is a gas cloud

around three times the mass of the Earth.

It seems they have discovered what is the great Holy Grail

for black hole scientists.

It almost goes straight in.

Who aims that well, we don't know. It's remarkable.

It's almost straight in, not quite but pretty much,

and so that means it will go deep, deep into the centre of potential

and therefore be sort of, if you like, a test, a test particle

for us to probe the environment of the black hole.

The gas cloud is advancing at speeds of over 2,000 kilometres per second.

The team are cautiously optimistic the gas cloud

will continue to be shredded

by the extreme gravity surrounding the black hole,

with every possibility that some of it will eventually be swallowed.

It's clear that it will come very close to the black hole,

might even hit the black hole.

So maybe we actually are feeding the black hole here.

Now exactly how much and how fast and all this is completely unknown

and that's the excitement about it because we will learn about it.

We have basically a test experiment.

We know we have thrown, so to speak, at this black hole now

a certain amount of mass which we roughly know.

We know when it is and how close it comes

and we can test over time how much happened.

It's that chance to see a black hole feed at close range

that has shaken the community of astronomers

into an uncharacteristic fervour of excitement.

We are facing here a very unusual situation in astronomy,

namely that things are getting urgent.

I mean, we only have half a year left or so,

then you really want to observe it.

Most of the objects we observe in astronomy

are not evolving on the timescale of human life.

That means mostly

they look the same regardless if I look

or if my grandson would look or whatever, it would be the same.

But here we have an unusual case

that the situation will change dramatically and quickly

within a few years.

That gas cloud was a compact object in 2004

and probably it will be completely shredded in 2013.

No-one knows for sure what will happen.

An uncertainty that only adds to the sense of anticipation.

Is it a cloud or is it a star?

And I guess I'm of the opinion that this is a star,

a star that has material around it

but we know of other stars in this region that has material around it

so that wouldn't make it unusual.

If it's a star, the black hole might not get a bite at it.

As of now, no-one can be certain.

This is what makes science interesting

because it's a point where you get to gamble.

You get to make a bet. What is this?

What should happen next?

To stare into the void of a black hole,

to tumble through space before disappearing forever within it,

it's the prospect of catching that unique moment

that explains the excitement of this year's events.

What happens to matter once it's been swallowed, we will never know.

But it's what a black hole does as it feeds

that holds the true surprise.

It would prove to be key to revealing what black holes really are,

and their hidden role at the heart of galaxies.

That picture that matter gets sucked into a black hole,

that's one of the biggest confusions about black holes that's out there,

partially because of science fiction like Star Trek and things like that,

so for matter that's far away from a black hole,

it actually doesn't get sucked in.

It's very much like the planets in the solar system

going around the sun.

Things just go around and around and around and around.

The difference is that when you have a lot of gas,

a lot of stuff orbiting around the black hole,

there is a little bit of friction

that causes matter to slowly spiral in towards the black hole.

As gas continues to spiral in towards the event horizon,

gravity climbs to staggering extremes.

Gas molecules are forced into a whirlpool

as they queue up to be devoured by the black hole.

Friction between gas particles in this cosmic waiting line

produces the densest, hottest most electrically-charged environment

to be found anywhere in the universe.

Friction between different parts of the gas cause it to heat up

and it's very much like

when the Apollo rockets returned to the Earth

and travelled through the Earth's atmosphere.

As they ploughed through the Earth's atmosphere they heat up

because of the friction between the satellite

and the atmosphere of the Earth.

What we know is that the hotter something gets,

the brighter it gets, the more light it emits.

Under the intense gravitational fields

at the entrance to the black hole,

the dense super-heated disc of matter waiting to be swallowed

begins to shine like a sun, but a sun like no other.

Here then is the strange paradox of black holes,

that a feeding black hole is anything but black.

Just how greedy and bright a black hole can get is revealed by

an outwardly very ordinary-looking galaxy called Cygnus A,

some 650 million light years away.

If we look at it with visible light,

we see that the inner parts of that galaxy,

maybe a few 10,000 light years across,

is kind of ordinary.

There are stars, there's gas, there's dust.

It's a sort of indiscriminately messy place

but it's not that special.

Now if we look in different wavelengths,

for example in radio waves, we see something completely different.

Cygnus A transforms into something else entirely.

What we see is no longer the galaxy with its stars

but instead we see an extreme structure

spread across intergalactic space and this structure is enormous.

It stretches 500,000 light years across

and it consists of these enormous lobes of brightness,

linked together by what looks like a thread of light

leading to a tiny bright point at the very centre of the Cygnus A galaxy.

This structure is enormously luminous

and there's also a huge amount of energy

just in the particles themselves

because they've been accelerated to close to the speed of light,

so if you add up all the energy in this great structure

it's probably at least a trillion times the amount of energy

that our sun puts out on a regular basis.

We now know this light is produced by the rotating disc of matter,

spinning round the edge of the black hole

at the heart of the Cygnus A galaxy waiting to be devoured.

It means that against all popular expectations,

the brightest sources of light in the universe

are actually black holes.

That fundamental fact is one of the great surprises about black holes.

You know, by their very name

you would think that black holes would be these dark objects

that wouldn't produce any light, and that's true.

If you just have a black hole sitting by itself, alone,

it doesn't produce any light

but in nature we have gas spiralling into black holes

and that turns out to produce the most efficient sources of light

and the brightest sources of light that we know of in the universe.

So here then was the answer to the great quasar mystery.

Quasars are nothing less than feeding supermassive black holes.

It was exactly what Donald Lynden-Bell had first predicted.

Behind every quasar is a black hole

and it took a long time for even astronomers to accept this

because it's quite a concept,

that there are these engines out there

that fit a variety of different situations

and produce some of the most energetic phenomena

we see in the universe.

Today the black hole at the centre of our galaxy is dark.

The super bright quasar phase having ended many billions of years ago

when the fuel that fires violent emissions was completely consumed.

But now, with the approaching gas cloud

and the prospect of feeding,

the black hole should get brighter.

Exactly how much it's pretty hard to tell.

We know roughly the amount of mass.

If you dump that amount of mass very quickly onto the black hole,

it will be a huge event.

I mean, the galactic centre of the black hole

would flare up by orders of magnitude.

A feeding binge on this scale is considered a low probability.

What astronomers consider to be more probable is that the black hole

will take snack-size nibbles out of the gas cloud.

It probably will take quite a while, so let's say ten years,

and so this whole event will then be stretched out

and therefore at any given time a little less spectacular,

but we will see, I think we probably will see these effects.

And so this summer the world's most powerful telescopes

will be keenly trained on our galactic centre

as the predictions of astronomers are put to the test

in the fiery ordeal of actual events.

With the new understanding of the behaviour

of feeding black holes at the heart of galaxies,

an unexpected new story is now emerging,

a story that reaches right out to our own solar system

and surprisingly touches us, here on planet Earth.

Far from being violent agents of destruction,

it seems instead black holes might actually

be benign architects which have played a part

in the creation of galaxies, stars, and even of life itself.

One of the first scientists

to begin to see black holes in this different way was Dr John Magorrian.

He was fascinated by the mysterious relationship

between supermassive black holes and the galaxies around them.

The key breakthrough in his work

came with the availability of detailed images of remote galaxies,

produced by the new Hubble Space Telescope.

One way of thinking about this

is to imagine that galaxies are like miniature light bulbs out in space,

and so with earlier telescopes

you could see that there was a light bulb there

but then with newer telescopes such as the Hubble,

then we're able to look in more detail

at exactly what was going on inside the light bulb

so you maybe could make out details of the filaments,

of the wires inside and so on.

With these high-resolution images,

astronomers could compare the size of galaxies

to the size of the black hole at their centres.

Was there any connection between the two?

What Magorrian discovered was completely unexpected.

The relationship that we found

was essentially that the bigger the galaxy,

the bigger the black hole.

That's in its broadest terms.

If you want to be a bit more precise about it,

we found that the mass of the black hole

was very strongly related

to the mass of the surrounding galaxy.

There is a nice linear relationship between these two

with the mass of the black hole

being around about 0.5% of the mass of the host galaxy.

The relationship Magorrian had discovered between galaxies

and the tiny black holes at their centre

seemed so strange and odd

that Magorrian and his colleagues thought that they'd made a mistake.

It was like suggesting that something as tiny as a coin

could control something as massive as the Earth.

When we discovered this correlation

between black hole mass and galaxy mass, we were surprised.

Then that was immediately followed by nervousness.

The nervousness then started to give way to possible mild elation

that we'd discovered something new and fundamental.

That correlation became known as the Magorrian relationship,

and it did indeed point to something profound.

This is incredibly important

because it really meant

that there was something linking these tiny supermassive black holes

in the centre of galaxies with the whole galaxy itself.

It meant that somehow their whole history had been intertwined,

that the growth of the galaxies

and the growth of the black holes was somehow related.

There was now a pressing challenge

to understand how black holes

and their surrounding galaxies

could be so intertwined.

Professor Andy Fabian of Cambridge University

is one astronomer who began to look.

Like the ripples that travel out from his paddles,

it's the extreme radiation pulsing out of black holes

that Fabian turned to for clues.

To see that radiation clearly,

you need to look beyond the ordinary light of the stars

at one kind of emission

that's the fiery signature of feeding black holes.

Stars and everything are beautiful,

make galaxies and that,

but there's a lot of other things going on out there,

and enormous amounts of energy being released

which we can only be aware of if we look with X-ray eyes.

One cluster of galaxies in particular, Perseus,

is a long-standing object of fascination.

250 million light years away,

Fabian has spent over 40 years

studying this fascinating piece of the sky.

What's intriguing is this thing here.

This is the central galaxy in the Perseus cluster

and the fact that it's got all this red and blue stuff going around it

means there's something going on.

The fiery monster hiding at the heart of Perseus

was only revealed when Fabian was able to look at the cluster

in the X-ray part of the spectrum.

What we could see was unexpected.

The X-ray image revealed

how the black hole at the heart of the galaxy

was firing unimaginable amounts of radiation into surrounding space,

and with extraordinary consequences.

We could see what was going on at the centre

and we could start to understand how the black hole

was feeding energy out into all the surrounding gas.

What the image had captured was the mechanism by which

a feeding black hole can dominate everything around it.

What it's doing is blowing bubbles at the centre of the cluster,

and those bubbles are then expanding and growing

like a pair of bubbles might be formed in a fish tank aerator.

The dark areas in the image

represent bubbles of super-heated gas,

showing how the black hole blasts away matter from the centre.

With each bubble almost the size of our own Milky Way,

it is doing so across extraordinary distances.

So this is showing you the scale.

We're seeing the black hole at the centre

having a galaxy-wide effect on the surroundings.

It's obvious in this image.

I don't need to tell you any more because you can see it.

What the image points to

is an explanation for the strange correlation

between the mass of a black hole

and the mass of its surrounding galaxy.

Galaxies could, in a way, be much bigger than they currently are.

Something is stopping them growing larger,

and that something is the black hole at the centre.

Now this is bizarre

because the ratio of the size of the black hole

to the size of the galaxy

is the same as the ratio between a grape,

or something this big, and the size of the Earth.

Now you might think that it's impossible for something that small

to control something that large but that's what appears to be happening.

As the black hole begins to devour matter,

so it starts to pour out energy.

Like a cosmic brew,

that energy sweeps matter back out from the centre of the galaxy,

preventing it from clumping together to form new stars.

The conclusion of this is that the total number of stars

that form in a galaxy appears to be stopped, truncated

by the power of the black hole at the centre.

The discovery of that relationship

has turned every preconception

about the nature of black holes on its head.

Instead of being strange, cosmic aberrations,

black holes have moved to the very centre

of the story of galaxies and stars,

a story that must include our own solar system.

And that must mean that in some way

our own black hole must have played a part

in what is perhaps the greatest mystery of all.

To walk here on Earth,

to be alive,

is thanks to a long chain of cause and effect

written deep into the structure of the universe,

a primordial process so long and so ancient

that on the scale of a human life, it seems almost incomprehensible.

One of the most amazing things in our universe

is that we are made of stars.

The heavy elements in our bodies, the carbon and the oxygen

and the nitrogen used to be millions of miles down inside stars.

So our existence here on this planet

relies on a deep history of stars being born,

creating new elements,

and then spitting those elements back out into the cosmos

where they're in turn recycled many, many times.

Over and over again, for almost 14 billion years,

ever since the beginning of the universe

and the formation of the first stars,

black holes have influenced this cosmic recycling process.

And since the elements forged in those stars

ended up inside planets like our own,

it means our black hole must have created the conditions

to make it just right for life to emerge here on Earth.

We're very lucky

we're not close by enough to one that's in a feeding frenzy,

that we get washed across by this destructive radiation

that will tear apart our molecules and our atmosphere,

and basically leave us in a barren place.

And then there's the other extreme where things are extremely quiet

and cold and maybe there haven't been that many stars formed ever,

because nothing stirred it up and nothing really got processes going

that would make all the elements

and make new generations of planets and so on.

It means our black hole must have left its fingerprints

on the unique chemistry that made possible

the first stirrings of life here on Earth.

If you look at the Milky Way Galaxy,

it's this interesting balance point,

it's this place where there's just enough wash from the black hole

to keep things interesting,

to possibly make the environment that allows us to exist here.

-NEWSREADER:

-'Astronomers are eagerly awaiting

'a spectacular fireworks display

'as a supermassive black hole at the centre of our galaxy... '

For the coming months across the world,

astronomers will be turning their telescopes

towards the centre of the Milky Way

ready to be awed by this historic chance

to witness a black hole sitting down to feed.

'..a vast cloud of interstellar dust and gas.'

It's the culmination of a 40-year journey

to get closer to that tantalising edge

between the universe that we can see and understand,

and that place of extremes that will forever be unseen and unknowable.

We tend to think of black holes

as these incredibly destructive, chaotic objects

but now we understand that they're actually an integral part

of why galaxies are the way they are.

20 years ago

black holes were seen as a possible ornament

in the middle of a galaxy.

Now we know that they may be the absolute machine,

the driving force for the eventual size

and possibly the shape of the galaxy.

The story of black holes that began as just this idea,

this thing that sprung out of pure human thought and mathematics,

and at first was seen too outrageous to be possible,

and over time we've learnt that not only are these things out there,

but they play this vital, important role that we're still learning about,

we're still discovering almost every day something new

about supermassive black holes and what they do in the universe.

Who knows what we're actually going to ultimately find out about them!

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