Horizon (1964–…): Season 49, Episode 16 - Swallowed by a Black Hole - full transcript
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!
Subtitles by Red Bee Media Ltd
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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