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Nothing is more seductive
than the unknown.

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Nothing more compelling
than a place of danger

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that lies beyond
normal comprehension.

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Of all those places,

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perhaps the strangest of all

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are black holes.

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They are an exit point
from the universe.

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Hidden trap doors
in the fabric of space-time.

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What would it be like
to enter the void

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and succumb to
a black hole's dark mysteries?

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Now, for the first time,

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astronomers are set to find out.

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

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is about to yield up its secrets.

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

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a violent drama is about to unfold.

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Our supermassive black hole
is getting ready to have dinner,

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as a gas cloud three times
the size of the Earth

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is caught in its gravitational hold.

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Across the world astronomers
are getting ready to discover

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what happens when
a black hole gets ready to feed.

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

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

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that we see how a black hole
starts getting fat.

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That would really be fantastic

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

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

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it will be possible
to witness and record the workings

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of one of these
great gravitational engines.

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Some of the excitement

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is just childish pleasure

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

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

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This is the first time
really in human history

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

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but that we are prepared
with the right sort of technology

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to see the details unfold.

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

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The disturbing truth
about black holes

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is that they're a boundary
between the known universe

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

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They are an anomaly
of gravity so strange,

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it is barely possible to comprehend.

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Black holes represent

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the regions where our current
theories of physics completely fail.

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What actually happens there,
we don't know,

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so it's this very weird situation

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where our understanding
kind of predicts its own failure.

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What gravity tells us

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is that everything
at the centre of a black hole

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should get smashed together
in a region

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smaller than even
a proton or an electron

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or any kind
of regular part of matter.

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

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

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

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The great dream for astronomers

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is to see those final moments

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as it falls over the edge
into oblivion.

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The kind of ideal situation
that we're aiming for

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is to really be able
to see what happens

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very close to the event horizon
of a black hole.

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

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so the only hope

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is to use observations
of black holes in the universe

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to actually see what's happening,

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and that is kind of the Holy Grail

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of astronomical observations
of black holes.

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

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might now be possible,

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

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to wrestle these
dark dragons of the cosmos

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into the realms
of scientific reality.

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

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that made no sense to anyone.

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

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that made it possible
to see the universe

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in a completely different way.

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Almost immediately they began
to detect a series of strange,

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previously unseen, sources of light.

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Nothing had ever been seen
like them.

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These things looked
very different, very strange,

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much more powerful,
much larger and really different

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than sorts of galaxies and stars
in our neighbourhood.

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But that was not the only surprise.

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

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or they looked like stars,

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were actually putting out
as much energy as a hundred galaxies

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

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

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

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

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They were given the name quasars.

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Quasars became
a very big and deep mystery

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because they were distant
in the universe

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and therefore
we were seeing the universe

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as it was billions of years ago

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and they were more potent,
more luminous

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than anything else
that we'd come across before.

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

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that would eventually lead to us
observing the strange behaviour

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of our own feeding black hole.

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So that's twice times
Newton's constant,

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onto the mass of the black hole

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and if you divide...

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What was first needed
was a maverick insight

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from one of modern science's
truly original thinkers.

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

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

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but none of them
was terribly convincing.

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

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was THE hot topic in astronomy
during the 1960s,

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as astronomers began to grapple
with the new enigmatic objects

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that had been found
by the radio telescopes.

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One astronomer keen
to have a crack at the problem

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was a young researcher
called Donald Lynden-Bell.

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The sky looked totally different

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in the radio than
it looked in the optical,

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and that was a big problem,

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and the question was,
what were these things?

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While his colleagues
were staring down telescopes,

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Lynden-Bell approached the problem
through theory.

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

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could possibly be so bright.

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

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and it came from a very small size.

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Now, putting those numbers together,

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one could already see

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the mass of the energy required
to give the emission

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

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But the problem was
that quasars are tiny in size,

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with nothing like
the scale of ten million suns.

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Lynden-Bell realised
that there was only one thing

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

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those mathematical anomalies
conjured up by theorists

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that had been predicted
but never observed:

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supermassive black holes.

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It suggested a baffling paradox,

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that quasars
are really shining black holes

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capable of emitting
the energy of entire galaxies.

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But Lynden-Bell then went further.

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I predicted that there
would be these massive objects

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found in the nearby galaxies.

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He brought his ideas together
with a bold conceptual leap

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

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Typically a large galaxy
would have a black hole,

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

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

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It was a pretty bold prediction.

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Yeah, well,
I come from a military family!

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

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Inside the centre of
every large galaxy in the universe

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lurks a supermassive black hole.

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If Lynden-Bell was right

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

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

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in the middle of
the hundreds of billions of stars

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that form our own galaxy,
the Milky Way.

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The problem was trying to map
our galaxy from the outside

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when we can only view it
from within.

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Seeing round that obstacle

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would take ingenuity
and some careful observations.

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

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is that because we're inside it,

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

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

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But if you look carefully

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

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They're gathered together

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

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That bright strip across the sky,

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with its extraordinary abundance
of stars and clusters,

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was a clue
to the nature of our galaxy.

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It was obvious to astronomers
for quite a long time

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

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and that we were within that disc.

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

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And then in the early 20th century,

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an American astronomer
called Harlow Shapley

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hit on a way of trying to find out

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where the centre
of the galaxy might be.

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He used objects
called globular clusters

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which are actually
found all over the sky.

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Bright sources
containing thousands of stars,

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globular clusters,

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

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Shapley realised
they were in effect signposts

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to where the centre
of the galaxy could be found.

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He plotted where the clusters were

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

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they were concentrated
in a particular direction.

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

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

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So at last

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astronomers knew exactly
where the centre of the galaxy was,

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

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At last astronomers
had a map of our galaxy.

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A panorama of the Milky Way

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it would never be possible
to see from planet Earth.

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

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If we were ever
going to have a chance

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of seeing a black hole
at close range,

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according to theory,
it should be hiding right here.

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

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

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00:17:34,800 --> 00:17:38,720
The good news is that there
should be a supermassive black hole

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00:17:38,720 --> 00:17:40,920
somewhere at the centre
of the Milky Way Galaxy.

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

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00:17:46,960 --> 00:17:50,120
We know where
to point our telescopes.

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The bad news is
that the centre of our galaxy

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is an incredibly
crowded and busy place.

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

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00:18:02,840 --> 00:18:05,240
than they are where we live
in the Milky Way Galaxy.

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00:18:05,240 --> 00:18:09,160
It's this incredibly confusing
and noisy environment.

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00:18:11,960 --> 00:18:14,480
The stars around the centre
of the Milky Way

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00:18:14,480 --> 00:18:17,000
are hundreds of times denser
than they are

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in the region around our sun.

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00:18:20,840 --> 00:18:24,760
Finding an invisible black hole
in all that swirling chaos

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would not be easy.

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It's like trying
to pick out an individual

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inside the middle of a busy city

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where there are lights and cars

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and things happening
all around them.

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But that wasn't the only problem.

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Vast swirling clouds of dust and gas
prevent visible light

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from the centre of our galaxy
from reaching us,

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making what lies beyond
hidden from view.

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

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It's putting a thick fog around that

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and so there's
only certain wavelengths of light

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that can penetrate through that.

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Without the means
to see through that dust,

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00:19:14,920 --> 00:19:17,960
the black hole that theory suggested

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should reside
at the centre of our Milky Way

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00:19:21,520 --> 00:19:26,160
would remain nothing more
than a bold but unproven idea.

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00:19:38,200 --> 00:19:41,640
With the quest to find
the black hole seemingly blocked,

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there was nevertheless
one glimmer of hope.

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00:19:46,080 --> 00:19:49,360
Now at least astronomers
had some sort of notion

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00:19:49,360 --> 00:19:50,520
where one should be hiding.

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00:19:52,600 --> 00:19:55,040
To tackle the problem,
what would be needed

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00:19:55,040 --> 00:19:58,080
was a new generation of telescopes

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00:19:58,080 --> 00:20:02,360
and that would take
a new generation of astronomers.

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00:20:02,360 --> 00:20:06,040
We were just at the point
where we had the technology

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00:20:06,040 --> 00:20:08,640
to address that question and so

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00:20:08,640 --> 00:20:10,120
in some sense it was,

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00:20:10,120 --> 00:20:13,280
I had the right hammer and
I was looking for the right nail.

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With her Los Angeles group,
Andrea Ghez

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began work on a telescope

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

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

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everything was falling into place
in terms of the ability

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to answer this question
at the centre of our galaxy.

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The telescopes were getting bigger

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so you had the ability
to see fine details.

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We had an explosion
in infra-red technology

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

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

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The challenge
was developing a telescope

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

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Using lasers
and specially-developed software,

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Ghez developed a telescope

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that made constant adjustments
to tune out atmospheric distortion.

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We had a huge amount of scepticism.

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No-one had ever done this,

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

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so you find somebody
that will help you out,

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

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to show that yes,
this technology will work,

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

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

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With her new telescope,
the final obstacle

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

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It was now possible
to see in unprecedented detail

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

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

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that's going to force these objects

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that are really close
to the black hole

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

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so the first thing you want to see

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is that there are
very fast moving objects

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where you think the black hole is.

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So, with our pictures that we took,

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

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You take one picture,

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you come back a year later,

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

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and what we see in this box

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are that there are stars
that are moving incredibly quickly.

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That was the first evidence
for the black hole.

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Once everything
had been plotted out,

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

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

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

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If there's a black hole,

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there is a further prediction
you can make

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about what these stars
are going to do.

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

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

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move on more than
just straight lines.

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As part of their travel
around the black hole,

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these stars are going to move
around the black hole

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

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

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

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

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In fact from these images

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you can actually tell
where the black hole is.

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

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It was a stunning discovery.

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After a quest lasting decades,

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Donald Lynden-Bell
had been proved right.

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Here indeed,
just where he had predicted,

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was a supermassive black hole.

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

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has suddenly become
even more exciting.

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That's because out there in space

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something is about to happen

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

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to reveal them as they really are.

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The reason for the excitement

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is all because of
a discovery made in Munich.

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Here a group working with
the European Space Observatory

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had shared credit
for discovering the black hole

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at the heart of the Milky Way.

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In late 2011, they made
an almost accidental discovery,

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

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It was while reviewing some data

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which had previously
been dismissed as second rate

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that they noticed something unusual.

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We decided in 2011

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

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data which is of somewhat lower
quality because the resolution

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

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

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which was very close
to the black hole.

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

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Instead it seemed to be a gas cloud

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

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

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We see that this gas cloud
as it moves

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

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like you see it in school books,

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according to the tidal shear,
as we say,

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the tidal disruption
by the black hole.

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It was moving quite fast

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

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and that's a very, very bad sign

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

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

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It's pretty much directly head-on

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moving towards the centre of gravity,
the black hole.

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

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around three times
the mass of the Earth.

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It seems they have discovered
what is the great Holy Grail

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for black hole scientists.

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It almost goes straight in.

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

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

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

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

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for us to probe
the environment of the black hole.

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

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The team are cautiously optimistic
the gas cloud

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will continue to be shredded

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by the extreme gravity
surrounding the black hole,

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

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00:28:41,440 --> 00:28:45,160
It's clear that it will come
very close to the black hole,

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might even hit the black hole.

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So maybe we actually
are feeding the black hole here.

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

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

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We have basically a test experiment.

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

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a certain amount of mass
which we roughly know.

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00:29:08,160 --> 00:29:09,960
We know when it is
and how close it comes

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and we can test over time
how much happened.

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

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that has shaken
the community of astronomers

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into an uncharacteristic
fervour of excitement.

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We are facing here a very
unusual situation in astronomy,

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namely that things
are getting urgent.

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

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then you really want to observe it.

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Most of the objects
we observe in astronomy

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are not evolving
on the timescale of human life.

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That means mostly

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they look the same
regardless if I look

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

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But here we have an unusual case

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that the situation will change
dramatically and quickly

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within a few years.

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00:30:01,160 --> 00:30:04,400
That gas cloud
was a compact object in 2004

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00:30:04,400 --> 00:30:07,400
and probably it will be
completely shredded in 2013.

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00:30:10,920 --> 00:30:13,640
No-one knows for sure
what will happen.

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An uncertainty that only adds
to the sense of anticipation.

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Is it a cloud or is it a star?

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00:30:23,520 --> 00:30:27,320
And I guess I'm of the opinion
that this is a star,

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a star that has material around it

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00:30:32,240 --> 00:30:36,280
but we know of other stars in this
region that has material around it

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so that wouldn't make it unusual.

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00:30:39,240 --> 00:30:43,400
If it's a star, the black hole
might not get a bite at it.

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00:30:43,400 --> 00:30:46,840
As of now, no-one can be certain.

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00:30:46,840 --> 00:30:48,840
This is what makes
science interesting

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00:30:48,840 --> 00:30:51,800
because it's a point
where you get to gamble.

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00:30:51,800 --> 00:30:53,920
You get to make a bet. What is this?

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00:30:53,920 --> 00:30:55,920
What should happen next?

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00:31:09,960 --> 00:31:14,080
To stare into the void
of a black hole,

408
00:31:14,080 --> 00:31:18,880
to tumble through space before
disappearing forever within it,

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00:31:18,880 --> 00:31:23,360
it's the prospect
of catching that unique moment

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that explains the excitement
of this year's events.

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

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

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that holds the true surprise.

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

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00:32:07,240 --> 00:32:11,080
and their hidden role
at the heart of galaxies.

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That picture that matter
gets sucked into a black hole,

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

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

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00:32:45,080 --> 00:32:47,800
so for matter
that's far away from a black hole,

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it actually doesn't get sucked in.

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00:32:50,080 --> 00:32:52,840
It's very much like the planets
in the solar system

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going around the sun.

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Things just go around and around
and around and around.

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

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00:33:12,080 --> 00:33:16,120
a lot of stuff
orbiting around the black hole,

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there is a little bit of friction

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00:33:18,400 --> 00:33:23,320
that causes matter to slowly spiral
in towards the black hole.

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00:33:28,560 --> 00:33:32,960
As gas continues to spiral
in towards the event horizon,

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00:33:32,960 --> 00:33:37,280
gravity climbs
to staggering extremes.

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00:33:40,120 --> 00:33:43,320
Gas molecules
are forced into a whirlpool

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00:33:43,320 --> 00:33:47,000
as they queue up
to be devoured by the black hole.

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00:33:50,480 --> 00:33:55,560
Friction between gas particles
in this cosmic waiting line

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produces the densest, hottest most
electrically-charged environment

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00:34:01,760 --> 00:34:05,680
to be found anywhere
in the universe.

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00:34:07,560 --> 00:34:11,440
Friction between different parts
of the gas cause it to heat up

436
00:34:11,440 --> 00:34:13,640
and it's very much like

437
00:34:13,640 --> 00:34:16,080
when the Apollo rockets
returned to the Earth

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00:34:16,080 --> 00:34:18,640
and travelled through
the Earth's atmosphere.

439
00:34:24,440 --> 00:34:27,280
As they ploughed through the Earth's
atmosphere they heat up

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00:34:27,280 --> 00:34:29,560
because of the friction
between the satellite

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00:34:29,560 --> 00:34:31,480
and the atmosphere of the Earth.

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00:34:38,240 --> 00:34:40,640
What we know is that
the hotter something gets,

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00:34:40,640 --> 00:34:43,280
the brighter it gets,
the more light it emits.

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00:34:47,560 --> 00:34:50,200
Under the intense
gravitational fields

445
00:34:50,200 --> 00:34:52,480
at the entrance to the black hole,

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00:34:52,480 --> 00:34:56,920
the dense super-heated disc
of matter waiting to be swallowed

447
00:34:56,920 --> 00:35:03,600
begins to shine like a sun,
but a sun like no other.

448
00:35:19,440 --> 00:35:23,200
Here then is the strange paradox
of black holes,

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00:35:25,360 --> 00:35:30,600
that a feeding black hole
is anything but black.

450
00:35:37,280 --> 00:35:41,800
Just how greedy and bright
a black hole can get is revealed by

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00:35:41,800 --> 00:35:45,800
an outwardly very ordinary-looking
galaxy called Cygnus A,

452
00:35:45,800 --> 00:35:49,480
some 650 million light years away.

453
00:35:51,920 --> 00:35:54,000
If we look at it with visible light,

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00:35:54,000 --> 00:35:56,680
we see that the inner parts
of that galaxy,

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00:35:56,680 --> 00:35:59,640
maybe a few 10,000
light years across,

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00:35:59,640 --> 00:36:01,320
is kind of ordinary.

457
00:36:01,320 --> 00:36:03,520
There are stars, there's gas,
there's dust.

458
00:36:03,520 --> 00:36:06,520
It's a sort of
indiscriminately messy place

459
00:36:06,520 --> 00:36:08,600
but it's not that special.

460
00:36:10,280 --> 00:36:12,680
Now if we look
in different wavelengths,

461
00:36:12,680 --> 00:36:16,920
for example in radio waves, we see
something completely different.

462
00:36:18,760 --> 00:36:22,080
Cygnus A transforms
into something else entirely.

463
00:36:23,800 --> 00:36:27,680
What we see is no longer
the galaxy with its stars

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00:36:27,680 --> 00:36:30,360
but instead we see
an extreme structure

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00:36:30,360 --> 00:36:35,440
spread across intergalactic space
and this structure is enormous.

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00:36:35,440 --> 00:36:41,920
It stretches 500,000
light years across

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00:36:41,920 --> 00:36:46,360
and it consists of
these enormous lobes of brightness,

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00:36:46,360 --> 00:36:49,640
linked together by what looks like
a thread of light

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00:36:49,640 --> 00:36:54,200
leading to a tiny bright point at the
very centre of the Cygnus A galaxy.

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00:36:58,160 --> 00:37:00,600
This structure is enormously luminous

471
00:37:00,600 --> 00:37:02,400
and there's also
a huge amount of energy

472
00:37:02,400 --> 00:37:04,080
just in the particles themselves

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00:37:04,080 --> 00:37:07,600
because they've been accelerated
to close to the speed of light,

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00:37:07,600 --> 00:37:10,920
so if you add up all
the energy in this great structure

475
00:37:10,920 --> 00:37:14,440
it's probably at least
a trillion times the amount of energy

476
00:37:14,440 --> 00:37:16,760
that our sun
puts out on a regular basis.

477
00:37:28,720 --> 00:37:34,120
We now know this light is produced
by the rotating disc of matter,

478
00:37:34,120 --> 00:37:37,000
spinning round the edge
of the black hole

479
00:37:37,000 --> 00:37:42,480
at the heart of the Cygnus A galaxy
waiting to be devoured.

480
00:37:45,280 --> 00:37:49,360
It means that
against all popular expectations,

481
00:37:49,360 --> 00:37:52,760
the brightest sources of light
in the universe

482
00:37:52,760 --> 00:37:55,240
are actually black holes.

483
00:38:02,640 --> 00:38:08,200
That fundamental fact is one of the
great surprises about black holes.

484
00:38:08,200 --> 00:38:09,800
You know, by their very name

485
00:38:09,800 --> 00:38:13,520
you would think that black holes
would be these dark objects

486
00:38:13,520 --> 00:38:16,720
that wouldn't produce any light,
and that's true.

487
00:38:16,720 --> 00:38:20,200
If you just have a black hole
sitting by itself, alone,

488
00:38:20,200 --> 00:38:22,280
it doesn't produce any light

489
00:38:22,280 --> 00:38:25,920
but in nature we have gas
spiralling into black holes

490
00:38:25,920 --> 00:38:30,480
and that turns out to produce
the most efficient sources of light

491
00:38:30,480 --> 00:38:34,240
and the brightest sources of light
that we know of in the universe.

492
00:38:36,920 --> 00:38:41,520
So here then was the answer
to the great quasar mystery.

493
00:38:43,600 --> 00:38:48,440
Quasars are nothing less than
feeding supermassive black holes.

494
00:38:51,320 --> 00:38:56,520
It was exactly what Donald
Lynden-Bell had first predicted.

495
00:39:00,400 --> 00:39:04,720
Behind every quasar is a black hole

496
00:39:04,720 --> 00:39:08,920
and it took a long time
for even astronomers to accept this

497
00:39:08,920 --> 00:39:10,600
because it's quite a concept,

498
00:39:10,600 --> 00:39:13,440
that there are these engines
out there

499
00:39:13,440 --> 00:39:16,880
that fit a variety
of different situations

500
00:39:16,880 --> 00:39:19,320
and produce some of
the most energetic phenomena

501
00:39:19,320 --> 00:39:20,520
we see in the universe.

502
00:39:25,440 --> 00:39:30,440
Today the black hole at the centre
of our galaxy is dark.

503
00:39:31,920 --> 00:39:36,920
The super bright quasar phase having
ended many billions of years ago

504
00:39:36,920 --> 00:39:41,320
when the fuel that fires violent
emissions was completely consumed.

505
00:39:51,720 --> 00:39:54,840
But now,
with the approaching gas cloud

506
00:39:54,840 --> 00:39:58,320
and the prospect of feeding,

507
00:39:58,320 --> 00:40:01,720
the black hole should get brighter.

508
00:40:06,040 --> 00:40:08,360
Exactly how much
it's pretty hard to tell.

509
00:40:08,360 --> 00:40:10,320
We know roughly the amount of mass.

510
00:40:10,320 --> 00:40:13,320
If you dump that amount of mass
very quickly onto the black hole,

511
00:40:13,320 --> 00:40:14,880
it will be a huge event.

512
00:40:14,880 --> 00:40:17,720
I mean, the galactic centre
of the black hole

513
00:40:17,720 --> 00:40:19,680
would flare up
by orders of magnitude.

514
00:40:19,680 --> 00:40:24,280
A feeding binge on this scale
is considered a low probability.

515
00:40:25,560 --> 00:40:30,240
What astronomers consider to be more
probable is that the black hole

516
00:40:30,240 --> 00:40:34,480
will take snack-size nibbles
out of the gas cloud.

517
00:40:34,480 --> 00:40:38,320
It probably will take quite a while,
so let's say ten years,

518
00:40:38,320 --> 00:40:40,600
and so this whole event
will then be stretched out

519
00:40:40,600 --> 00:40:43,640
and therefore at any given time
a little less spectacular,

520
00:40:43,640 --> 00:40:46,920
but we will see, I think
we probably will see these effects.

521
00:40:50,320 --> 00:40:53,600
And so this summer
the world's most powerful telescopes

522
00:40:53,600 --> 00:40:57,360
will be keenly
trained on our galactic centre

523
00:40:57,360 --> 00:41:01,920
as the predictions
of astronomers are put to the test

524
00:41:01,920 --> 00:41:05,000
in the fiery ordeal
of actual events.

525
00:41:18,600 --> 00:41:20,600
With the new understanding
of the behaviour

526
00:41:20,600 --> 00:41:24,240
of feeding black holes
at the heart of galaxies,

527
00:41:24,240 --> 00:41:28,080
an unexpected new story
is now emerging,

528
00:41:28,080 --> 00:41:32,880
a story that reaches right out
to our own solar system

529
00:41:32,880 --> 00:41:37,360
and surprisingly touches us,
here on planet Earth.

530
00:41:42,800 --> 00:41:45,320
Far from being violent agents
of destruction,

531
00:41:45,320 --> 00:41:49,440
it seems instead black holes
might actually

532
00:41:49,440 --> 00:41:52,520
be benign architects
which have played a part

533
00:41:52,520 --> 00:41:58,920
in the creation of galaxies,
stars, and even of life itself.

534
00:42:07,680 --> 00:42:09,560
One of the first scientists

535
00:42:09,560 --> 00:42:14,200
to begin to see black holes in this
different way was Dr John Magorrian.

536
00:42:18,680 --> 00:42:21,760
He was fascinated by
the mysterious relationship

537
00:42:21,760 --> 00:42:25,760
between supermassive black holes
and the galaxies around them.

538
00:42:39,040 --> 00:42:40,920
The key breakthrough in his work

539
00:42:40,920 --> 00:42:46,120
came with the availability of
detailed images of remote galaxies,

540
00:42:46,120 --> 00:42:49,280
produced by
the new Hubble Space Telescope.

541
00:42:56,200 --> 00:42:57,920
One way of thinking about this

542
00:42:57,920 --> 00:43:02,120
is to imagine that galaxies are like
miniature light bulbs out in space,

543
00:43:02,120 --> 00:43:04,120
and so with earlier telescopes

544
00:43:04,120 --> 00:43:06,600
you could see
that there was a light bulb there

545
00:43:06,600 --> 00:43:09,720
but then with newer telescopes
such as the Hubble,

546
00:43:09,720 --> 00:43:12,200
then we're able
to look in more detail

547
00:43:12,200 --> 00:43:14,760
at exactly what was going on
inside the light bulb

548
00:43:14,760 --> 00:43:18,120
so you maybe could
make out details of the filaments,

549
00:43:18,120 --> 00:43:20,240
of the wires inside and so on.

550
00:43:22,440 --> 00:43:25,080
With these high-resolution images,

551
00:43:25,080 --> 00:43:28,560
astronomers could compare
the size of galaxies

552
00:43:28,560 --> 00:43:32,880
to the size
of the black hole at their centres.

553
00:43:36,560 --> 00:43:39,280
Was there any connection
between the two?

554
00:43:42,440 --> 00:43:46,600
What Magorrian discovered
was completely unexpected.

555
00:43:48,880 --> 00:43:50,120
The relationship that we found

556
00:43:50,120 --> 00:43:52,440
was essentially that
the bigger the galaxy,

557
00:43:52,440 --> 00:43:53,760
the bigger the black hole.

558
00:43:53,760 --> 00:43:55,800
That's in its broadest terms.

559
00:43:55,800 --> 00:43:58,040
If you want to be
a bit more precise about it,

560
00:43:58,040 --> 00:44:01,080
we found that the mass
of the black hole

561
00:44:01,080 --> 00:44:03,720
was very strongly related

562
00:44:03,720 --> 00:44:06,080
to the mass
of the surrounding galaxy.

563
00:44:06,080 --> 00:44:08,600
There is a nice linear relationship
between these two

564
00:44:08,600 --> 00:44:10,960
with the mass of the black hole

565
00:44:10,960 --> 00:44:15,280
being around about 0.5%
of the mass of the host galaxy.

566
00:44:18,760 --> 00:44:22,200
The relationship Magorrian
had discovered between galaxies

567
00:44:22,200 --> 00:44:24,800
and the tiny black holes
at their centre

568
00:44:24,800 --> 00:44:26,600
seemed so strange and odd

569
00:44:26,600 --> 00:44:30,680
that Magorrian and his colleagues
thought that they'd made a mistake.

570
00:44:32,720 --> 00:44:36,600
It was like suggesting
that something as tiny as a coin

571
00:44:36,600 --> 00:44:39,960
could control something
as massive as the Earth.

572
00:44:45,240 --> 00:44:47,200
When we discovered this correlation

573
00:44:47,200 --> 00:44:50,840
between black hole mass
and galaxy mass, we were surprised.

574
00:44:50,840 --> 00:44:53,800
Then that was immediately
followed by nervousness.

575
00:44:55,560 --> 00:44:59,960
The nervousness then started
to give way to possible mild elation

576
00:44:59,960 --> 00:45:02,600
that we'd discovered
something new and fundamental.

577
00:45:05,040 --> 00:45:09,120
That correlation became known
as the Magorrian relationship,

578
00:45:09,120 --> 00:45:12,800
and it did indeed point
to something profound.

579
00:45:14,480 --> 00:45:16,520
This is incredibly important

580
00:45:16,520 --> 00:45:18,440
because it really meant

581
00:45:18,440 --> 00:45:24,320
that there was something linking
these tiny supermassive black holes

582
00:45:24,320 --> 00:45:28,720
in the centre of galaxies
with the whole galaxy itself.

583
00:45:28,720 --> 00:45:33,000
It meant that somehow their
whole history had been intertwined,

584
00:45:33,000 --> 00:45:35,040
that the growth of the galaxies

585
00:45:35,040 --> 00:45:38,160
and the growth of the black holes
was somehow related.

586
00:45:44,640 --> 00:45:47,480
There was now a pressing challenge

587
00:45:47,480 --> 00:45:49,880
to understand how black holes

588
00:45:49,880 --> 00:45:51,920
and their surrounding galaxies

589
00:45:51,920 --> 00:45:54,360
could be so intertwined.

590
00:45:59,640 --> 00:46:02,720
Professor Andy Fabian
of Cambridge University

591
00:46:02,720 --> 00:46:04,720
is one astronomer
who began to look.

592
00:46:10,320 --> 00:46:13,920
Like the ripples
that travel out from his paddles,

593
00:46:13,920 --> 00:46:17,640
it's the extreme radiation
pulsing out of black holes

594
00:46:17,640 --> 00:46:19,960
that Fabian turned to for clues.

595
00:46:24,200 --> 00:46:26,800
To see that radiation clearly,

596
00:46:26,800 --> 00:46:29,920
you need to look beyond
the ordinary light of the stars

597
00:46:29,920 --> 00:46:31,720
at one kind of emission

598
00:46:31,720 --> 00:46:36,040
that's the fiery signature
of feeding black holes.

599
00:46:45,160 --> 00:46:46,800
Stars and everything are beautiful,

600
00:46:46,800 --> 00:46:48,280
make galaxies and that,

601
00:46:48,280 --> 00:46:50,480
but there's a lot of other things
going on out there,

602
00:46:50,480 --> 00:46:53,880
and enormous amounts of energy
being released

603
00:46:53,880 --> 00:46:56,960
which we can only be aware of
if we look with X-ray eyes.

604
00:47:02,480 --> 00:47:06,720
One cluster of galaxies
in particular, Perseus,

605
00:47:06,720 --> 00:47:09,320
is a long-standing object
of fascination.

606
00:47:11,160 --> 00:47:13,600
250 million light years away,

607
00:47:13,600 --> 00:47:16,320
Fabian has spent over 40 years

608
00:47:16,320 --> 00:47:18,920
studying this fascinating piece
of the sky.

609
00:47:18,920 --> 00:47:23,600
What's intriguing
is this thing here.

610
00:47:23,600 --> 00:47:27,240
This is the central galaxy
in the Perseus cluster

611
00:47:27,240 --> 00:47:31,040
and the fact that it's got all this
red and blue stuff going around it

612
00:47:31,040 --> 00:47:32,960
means there's something going on.

613
00:47:39,680 --> 00:47:42,560
The fiery monster hiding
at the heart of Perseus

614
00:47:42,560 --> 00:47:46,720
was only revealed when Fabian
was able to look at the cluster

615
00:47:46,720 --> 00:47:49,360
in the X-ray part of the spectrum.

616
00:47:57,840 --> 00:48:00,640
What we could see was unexpected.

617
00:48:04,080 --> 00:48:05,840
The X-ray image revealed

618
00:48:05,840 --> 00:48:08,880
how the black hole
at the heart of the galaxy

619
00:48:08,880 --> 00:48:14,000
was firing unimaginable amounts
of radiation into surrounding space,

620
00:48:14,000 --> 00:48:17,000
and with extraordinary consequences.

621
00:48:22,360 --> 00:48:25,880
We could see what
was going on at the centre

622
00:48:25,880 --> 00:48:30,000
and we could start to understand
how the black hole

623
00:48:30,000 --> 00:48:34,080
was feeding energy out
into all the surrounding gas.

624
00:48:36,600 --> 00:48:40,000
What the image had captured
was the mechanism by which

625
00:48:40,000 --> 00:48:44,760
a feeding black hole
can dominate everything around it.

626
00:48:47,040 --> 00:48:51,760
What it's doing is blowing bubbles
at the centre of the cluster,

627
00:48:51,760 --> 00:48:56,080
and those bubbles
are then expanding and growing

628
00:48:56,080 --> 00:49:00,320
like a pair of bubbles might be
formed in a fish tank aerator.

629
00:49:04,200 --> 00:49:06,000
The dark areas in the image

630
00:49:06,000 --> 00:49:09,000
represent bubbles
of super-heated gas,

631
00:49:09,000 --> 00:49:13,080
showing how the black hole
blasts away matter from the centre.

632
00:49:15,920 --> 00:49:19,760
With each bubble almost
the size of our own Milky Way,

633
00:49:19,760 --> 00:49:23,600
it is doing so
across extraordinary distances.

634
00:49:27,680 --> 00:49:29,920
So this is showing you the scale.

635
00:49:29,920 --> 00:49:33,200
We're seeing the black hole
at the centre

636
00:49:33,200 --> 00:49:37,200
having a galaxy-wide effect
on the surroundings.

637
00:49:37,200 --> 00:49:38,680
It's obvious in this image.

638
00:49:38,680 --> 00:49:41,680
I don't need to tell you any more
because you can see it.

639
00:49:44,720 --> 00:49:46,360
What the image points to

640
00:49:46,360 --> 00:49:49,200
is an explanation
for the strange correlation

641
00:49:49,200 --> 00:49:50,880
between the mass of a black hole

642
00:49:50,880 --> 00:49:53,680
and the mass
of its surrounding galaxy.

643
00:49:58,160 --> 00:50:03,040
Galaxies could, in a way, be
much bigger than they currently are.

644
00:50:03,040 --> 00:50:05,680
Something is stopping them
growing larger,

645
00:50:05,680 --> 00:50:09,280
and that something
is the black hole at the centre.

646
00:50:09,280 --> 00:50:10,960
Now this is bizarre

647
00:50:10,960 --> 00:50:14,440
because the ratio of the size
of the black hole

648
00:50:14,440 --> 00:50:16,240
to the size of the galaxy

649
00:50:16,240 --> 00:50:19,680
is the same as the ratio
between a grape,

650
00:50:19,680 --> 00:50:22,760
or something this big,
and the size of the Earth.

651
00:50:22,760 --> 00:50:27,280
Now you might think that it's
impossible for something that small

652
00:50:27,280 --> 00:50:31,640
to control something that large but
that's what appears to be happening.

653
00:50:35,360 --> 00:50:39,080
As the black hole
begins to devour matter,

654
00:50:39,080 --> 00:50:41,320
so it starts to pour out energy.

655
00:50:43,920 --> 00:50:46,080
Like a cosmic brew,

656
00:50:46,080 --> 00:50:50,360
that energy sweeps matter back out
from the centre of the galaxy,

657
00:50:50,360 --> 00:50:53,840
preventing it from clumping together
to form new stars.

658
00:50:57,680 --> 00:51:00,920
The conclusion of this is
that the total number of stars

659
00:51:00,920 --> 00:51:04,800
that form in a galaxy
appears to be stopped, truncated

660
00:51:04,800 --> 00:51:07,800
by the power of the black hole
at the centre.

661
00:51:12,680 --> 00:51:15,280
The discovery of that relationship

662
00:51:15,280 --> 00:51:16,960
has turned every preconception

663
00:51:16,960 --> 00:51:19,560
about the nature
of black holes on its head.

664
00:51:21,640 --> 00:51:25,440
Instead of being
strange, cosmic aberrations,

665
00:51:25,440 --> 00:51:28,920
black holes have moved
to the very centre

666
00:51:28,920 --> 00:51:32,000
of the story of galaxies and stars,

667
00:51:32,000 --> 00:51:35,640
a story that must include
our own solar system.

668
00:51:37,760 --> 00:51:41,960
And that must mean that in some way

669
00:51:41,960 --> 00:51:45,200
our own black hole
must have played a part

670
00:51:45,200 --> 00:51:49,000
in what is perhaps
the greatest mystery of all.

671
00:52:05,040 --> 00:52:07,600
To walk here on Earth,

672
00:52:07,600 --> 00:52:10,000
to be alive,

673
00:52:10,000 --> 00:52:13,040
is thanks to a long chain
of cause and effect

674
00:52:13,040 --> 00:52:18,240
written deep into the structure
of the universe,

675
00:52:18,240 --> 00:52:22,280
a primordial process
so long and so ancient

676
00:52:22,280 --> 00:52:28,440
that on the scale of a human life,
it seems almost incomprehensible.

677
00:52:33,560 --> 00:52:36,280
One of the most amazing things
in our universe

678
00:52:36,280 --> 00:52:38,200
is that we are made of stars.

679
00:52:39,640 --> 00:52:43,280
The heavy elements in our bodies,
the carbon and the oxygen

680
00:52:43,280 --> 00:52:47,760
and the nitrogen used to be
millions of miles down inside stars.

681
00:52:50,160 --> 00:52:53,680
So our existence here on this planet

682
00:52:53,680 --> 00:52:57,840
relies on a deep
history of stars being born,

683
00:52:57,840 --> 00:53:00,160
creating new elements,

684
00:53:00,160 --> 00:53:02,960
and then spitting those elements
back out into the cosmos

685
00:53:02,960 --> 00:53:05,600
where they're in turn
recycled many, many times.

686
00:53:09,520 --> 00:53:14,600
Over and over again,
for almost 14 billion years,

687
00:53:14,600 --> 00:53:16,720
ever since
the beginning of the universe

688
00:53:16,720 --> 00:53:19,440
and the formation
of the first stars,

689
00:53:19,440 --> 00:53:24,160
black holes have influenced
this cosmic recycling process.

690
00:53:26,760 --> 00:53:29,360
And since the elements
forged in those stars

691
00:53:29,360 --> 00:53:31,440
ended up inside
planets like our own,

692
00:53:31,440 --> 00:53:37,160
it means our black hole
must have created the conditions

693
00:53:37,160 --> 00:53:42,320
to make it just right
for life to emerge here on Earth.

694
00:53:47,880 --> 00:53:49,280
We're very lucky

695
00:53:49,280 --> 00:53:52,760
we're not close by enough to one
that's in a feeding frenzy,

696
00:53:52,760 --> 00:53:55,400
that we get washed across
by this destructive radiation

697
00:53:55,400 --> 00:53:57,920
that will tear apart
our molecules and our atmosphere,

698
00:53:57,920 --> 00:54:01,040
and basically leave us
in a barren place.

699
00:54:03,760 --> 00:54:07,520
And then there's the other extreme
where things are extremely quiet

700
00:54:07,520 --> 00:54:11,360
and cold and maybe there haven't been
that many stars formed ever,

701
00:54:11,360 --> 00:54:15,280
because nothing stirred it up and
nothing really got processes going

702
00:54:15,280 --> 00:54:17,040
that would make all the elements

703
00:54:17,040 --> 00:54:19,160
and make new generations
of planets and so on.

704
00:54:23,440 --> 00:54:26,960
It means our black hole
must have left its fingerprints

705
00:54:26,960 --> 00:54:29,720
on the unique chemistry
that made possible

706
00:54:29,720 --> 00:54:32,400
the first stirrings
of life here on Earth.

707
00:54:37,200 --> 00:54:40,280
If you look at the Milky Way Galaxy,

708
00:54:40,280 --> 00:54:42,160
it's this interesting balance point,

709
00:54:42,160 --> 00:54:45,640
it's this place where there's
just enough wash from the black hole

710
00:54:45,640 --> 00:54:47,080
to keep things interesting,

711
00:54:47,080 --> 00:54:50,920
to possibly make the environment
that allows us to exist here.

712
00:55:03,920 --> 00:55:07,240
NEWSREADER: 'Astronomers
are eagerly awaiting

713
00:55:07,240 --> 00:55:09,560
'a spectacular fireworks display

714
00:55:09,560 --> 00:55:12,760
'as a supermassive black hole
at the centre of our galaxy... '

715
00:55:12,760 --> 00:55:15,240
For the coming months
across the world,

716
00:55:15,240 --> 00:55:17,720
astronomers will be
turning their telescopes

717
00:55:17,720 --> 00:55:20,320
towards the centre of the Milky Way

718
00:55:20,320 --> 00:55:22,680
ready to be awed
by this historic chance

719
00:55:22,680 --> 00:55:26,160
to witness a black hole
sitting down to feed.

720
00:55:27,920 --> 00:55:30,440
'..a vast cloud
of interstellar dust and gas.'

721
00:55:34,120 --> 00:55:36,360
It's the culmination
of a 40-year journey

722
00:55:36,360 --> 00:55:39,240
to get closer
to that tantalising edge

723
00:55:39,240 --> 00:55:45,040
between the universe
that we can see and understand,

724
00:55:45,040 --> 00:55:52,400
and that place of extremes that will
forever be unseen and unknowable.

725
00:56:06,400 --> 00:56:07,840
We tend to think of black holes

726
00:56:07,840 --> 00:56:12,000
as these incredibly
destructive, chaotic objects

727
00:56:12,000 --> 00:56:15,480
but now we understand that
they're actually an integral part

728
00:56:15,480 --> 00:56:17,520
of why galaxies
are the way they are.

729
00:56:22,080 --> 00:56:23,640
20 years ago

730
00:56:23,640 --> 00:56:26,600
black holes
were seen as a possible ornament

731
00:56:26,600 --> 00:56:28,640
in the middle of a galaxy.

732
00:56:28,640 --> 00:56:32,640
Now we know that
they may be the absolute machine,

733
00:56:32,640 --> 00:56:35,880
the driving force
for the eventual size

734
00:56:35,880 --> 00:56:39,000
and possibly the shape
of the galaxy.

735
00:56:42,800 --> 00:56:46,640
The story of black holes
that began as just this idea,

736
00:56:46,640 --> 00:56:50,920
this thing that sprung out of
pure human thought and mathematics,

737
00:56:50,920 --> 00:56:53,560
and at first was seen
too outrageous to be possible,

738
00:56:53,560 --> 00:56:57,400
and over time we've learnt that not
only are these things out there,

739
00:56:57,400 --> 00:57:02,080
but they play this vital, important
role that we're still learning about,

740
00:57:02,080 --> 00:57:05,120
we're still discovering
almost every day something new

741
00:57:05,120 --> 00:57:08,600
about supermassive black holes
and what they do in the universe.

742
00:57:10,640 --> 00:57:13,560
Who knows what we're actually going
to ultimately find out about them!

743
00:57:33,960 --> 00:57:38,440
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