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Two black holes
circle each other

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in a dance of death.

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They spiral inwards,

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their immense gravities
pulling them ever closer.

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When they finally collide,

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it's one of the most
powerful events

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since the big bang.

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This explosive mystery

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sends ripples
across the world of science.

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But can it also answer

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one of the most pressing
questions in cosmology?

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How do supermassive
black holes grow so large?

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In the known universe,

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there are roughly
2,000 billion galaxies.

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Each one has a different
shape and size.

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But they may all have
one feature in common...

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a supermassive black hole
buried at their center.

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As its name says,
it is supermassive.

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And here, we're talking
about objects

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that are millions
or billions of times

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the mass of the Sun.

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Supermassive black holes

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are so big
that we need a special scale

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for measuring them.

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A solar mass
is the mass of the Sun.

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So when we study the universe,

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we have to use the tools
that we have in hand.

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And what's the most massive
thing that we have around us?

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It's the Sun.
And so we refer to things

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in multiples
of the mass of the Sun

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because it just makes it easier
to wrap our heads around.

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However, if you have something
that's 17 billion times

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the mass of the Sun,
that's pretty difficult

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to wrap your head around anyway.

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But we know that those
kinds of black holes

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live in the centers of galaxies.

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The supermassive black hole

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the milky way, is called
Sagittarius "a" -star.

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It weighs in
at 4 million solar masses.

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But compared to the other
supermassive black holes

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out there, it's puny.

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This is probably
one of the only contexts

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where you would think that
our supermassive black hole

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isn't very supermassive.

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The supermassive black hole

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in our neighboring galaxy,
Andromeda,

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is 25 times larger
than Sagittarius "A" -star,

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coming in at
100 million solar masses.

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But compared
to the largest monsters

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out in the universe,
it's a runt.

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O.J. 287's primary
supermassive black hole

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weighs in
at 18 billion solar masses.

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And the black hole
in the core of galaxy NGC 4889

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in the coma cluster
weighs 21 billion solar stars.

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That's over 5,000 times larger

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than Sagittarius "a" -star.

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These are incredible things

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that are more massive
than some galaxies.

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Now astronomers may have ma

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a giant, new
supermassive black hole

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that's a mind-blowing
30 billion times

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the mass of the Sun.

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It's a huge puzzle.

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And we have simply no idea
how it got so big.

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It's a huge mystery how black

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we started finding
black holes with millions

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and billions of times
the Sun's mass.

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No one expected that.

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And we have no idea
how they got to be so big.

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It's not entirely
clear at this point

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how supermassive black holes
can get to be the masses

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that they are today.

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Regular-sized black holes form

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when large stars over 20 times
the mass of our sun

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crash and burn.

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When a large star
runs out of fuel,

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the core stops generating
enough outward force

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to counteract the power
of gravity crushing inwards.

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As the star collapses,

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the outer part explodes
in a supernova.

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The inner core shrinks

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from a sphere
millions of miles wide

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to one just 10 miles across.

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It's like shrinking
the earth down

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to the size of a golf ball.

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This rapid collapse
creates a black hole.

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So we now have seen black holes

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that are solar-mass black
holes

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and black holes that are million

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or billion-solar-mass
black holes.

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And the question is, how do you
get from one to the other?

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Do the giants somehow grow

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from a solar-mass black hole?

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One of the big puzzles today is,

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how do you make one of these
supermassive black holes?

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One idea is,
you get there by starting

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with a solar-mass black hole,

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having it grow through a stage

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of being an intermediate-mass
black hole

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and then eventually
getting to be

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a supermassive black hole.

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Theoretically,
intermediate-mass black holes

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should be between 100
and 100,000 solar masses.

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But we've never seen one.

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Part of the mystery
of supermassive black holes

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is that black holes seem
to occur in two flavors.

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You have ones that are
only a couple times

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the mass of the Sun.

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And you have ones
that are millions

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or billions of times
the mass of the Sun.

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So we have small
and extra large.

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If we think
of the stellar-mass black hole

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as sort of the baby black holes,

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and the supermassive black holes
as the grown-up black holes,

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we're missing
the teenage black holes.

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Where are these black holes
that have masses

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that are between stellar mass
and supermassive?

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They're sort of like
a holy grail

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for black hole hunters.

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Where are these things?
Where can we find them?

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And how do you make them?

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Then astronomers caught a break.

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They picked up a burst of energy

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coming from the NGC 1399 galaxy.

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It was the death throes

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of a star being eaten
by a black hole.

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When they measured its size,
they discovered it was

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an elusive intermediate-mass
black hole.

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The missing link had been found.

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But when scientists did the math

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to see if such an
intermediate-mass black hole

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could grow into
a supermassive black hole,

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they hit a snag.

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There hasn't been enough time

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since the birth of the universe

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for an intermediate-mass
black hole

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to eat enough stars

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to grow into
a supermassive black hole.

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It doesn't seem like
there's enough time

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for black holes to get
as big as we see them.

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But supermassives
are everywhere we look.

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How did they get there?

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And how did they grow so huge?

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In our universe, we've
detected small black holes.

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And we've seen monsters,

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supermassive black holes

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billions of times
the mass of our sun.

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But we'd found
almost none in between.

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So how do you get from a small
black hole to a giant one?

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One of the most important
outstanding questions

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in cosmology is,

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how did supermassive black holes

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get as big as they are?

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And when did that happen?

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Black holes are normally S

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an all-you-can-eat buffet.

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One of the best ideas
for how black holes grow

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is that black holes do

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what we expect
black holes to do,

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and that is eat stuff.

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For a black hole,

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it's almost as if the universe
is its restaurant.

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And on its menu,
you'll find stars, planets,

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and clouds of gas and dust.

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So is binge-eating the answer

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to growing
a supermassive black hole?

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Theoretically, black holes
should keep on growing forever

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as they consume
more and more food.

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But recent discoveries suggest

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that the universe
puts them on a diet,

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controlling how much they eat.

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Black holes are hungry.
They like to eat.

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But sometimes,
they eat too much,

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and they burp it up.

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February 2015.

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Astronomers report
something unusual

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in the galaxy NGC 2276.

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It looked like something
had taken a bite

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out of one of its spiral arms.

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Sitting alone in the void

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was an intermediate-mass
black hole,

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about 50,000 times
the mass of the Sun.

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One theory
was that the black hole

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had eaten everything around it,

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creating the dead zone.

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But the detection
of a burst of energy

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from the black hole suggests

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it may have tried
to eat too much

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and, in the process,
destroyed its food source,

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burping so hard,
its food was blasted away.

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Turns out that black holes
are actually very messy

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a lot of matter gets thrown
off as it tries to absorb it.

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So things move in, gets hot.

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But then a lot of it gets
thrown all the way back out.

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Black holes
are not vacuums in space.

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They do not just eat
everything around them.

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And so they are messy.
Some things get in.

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And they take that on.
And it grows their mass.

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And some things are just
flung out as they're eating.

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The enormous gravity of black
holes sucks gas, dust,

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and even stars towards them.

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Everybody's been to
an all-you-can-eat buffet.

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But let's be honest.
There really is a limit

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to how much you can eat.

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Black holes
are gluttons. They're greedy.

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They don't really know
when they've eaten too much.

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They just keep on cramming in
more and more food.

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It doesn't just fall in.

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It has to go down the drain,
more or less.

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And so it forms this disk
around the hole.

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And as it does that,
there's a lot of turbulence

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and magnetic fields

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and a witch's brew of forces
going on there

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that get it really hot.

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As the gas
and dust swirls around,

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it heats up,

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pushing temperatures to
millions of degrees Fahrenheit.

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This swirl, called
the accretion disk,

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also generates powerful
magnetic fields.

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These fields are dragged
by the SPiN of the black hole

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and become focused
above the poles.

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As energy builds up,

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the magnetic fields
become so compressed

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they blast out
super-energized particles.

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These beams can actually
be incredibly violent.

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Matter is flung out

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at a large fraction
of the speed of light.

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It's a tremendous wind

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that blows very hard away
from the black hole.

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The jet hits the gas clouds

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surrounding the black hole,

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blowing the buffet away.

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If they eat too much,

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they can basically
blow everything

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that's in their vicinity away.

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They lose their food supply.
And then they're gonna starve.

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They can kind of shoot
themselves in the foot.

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With no food available,

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the black hole stops growing.

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Astronomers think
that's what happened

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00:12:03,999 --> 00:12:05,779
to the intermediate-mass
black hole

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they discovered
in the dead zone.

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These burps may
regulate star formation

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and stop the black hole
from getting obese.

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But over time,

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the black hole
will start eating again

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as gas falls back towards it.

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But can an intermediate-mass
black hole eat enough

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00:12:28,788 --> 00:12:31,388
to become
a supermassive black hole

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weighing billions
of solar masses?

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Could that black hole
become so obese by eating?

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00:12:38,551 --> 00:12:40,400
That's a really
interesting question.

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You'd have to eat
a heck of a lot

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to get that fat.

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When you think about it, if
you imagine an average galaxy

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00:12:48,917 --> 00:12:50,895
has 100 billion stars,

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the black hole
would have to eat one

258
00:12:52,617 --> 00:12:55,188
in every five stars
in the galaxy.

259
00:12:55,189 --> 00:12:57,859
The universe is old.
But is it really old enough

260
00:12:57,860 --> 00:13:01,717
that black holes have had time
to consume billions of stars?

261
00:13:01,727 --> 00:13:03,705
That seems kind of unlikely.

262
00:13:03,706 --> 00:13:05,416
It doesn't seem to add up.

263
00:13:05,417 --> 00:13:06,939
We need some other way

264
00:13:06,940 --> 00:13:08,918
to make these
supermassive black holes.

265
00:13:08,919 --> 00:13:12,015
And the question is,
what is that?

266
00:13:12,025 --> 00:13:14,656
Maybe we've been making
this all too complicated.

267
00:13:14,666 --> 00:13:19,275
Maybe to get a big black hole is
to start big in the first place.

268
00:13:19,285 --> 00:13:22,708
So how can black
holes start big?

269
00:13:22,717 --> 00:13:26,080
To answer that question,
scientists had to journey back

270
00:13:26,081 --> 00:13:28,622
to the very start
of the universe,

271
00:13:28,623 --> 00:13:32,154
to a mysterious time
called the dark ages.

272
00:13:51,492 --> 00:13:53,905
As we look out
into the universe,

273
00:13:53,906 --> 00:13:58,426
we're seeing farther
and farther back in time.

274
00:13:58,427 --> 00:13:59,711
We have now looked back

275
00:13:59,712 --> 00:14:02,817
over 12 billion years

276
00:14:02,818 --> 00:14:06,250
to the time when the cosmos
was still an infant.

277
00:14:06,251 --> 00:14:11,492
And what we found
was a huge surprise.

278
00:14:11,493 --> 00:14:13,075
We had made the assumption

279
00:14:13,076 --> 00:14:15,351
that as you look farther
out into the universe,

280
00:14:15,361 --> 00:14:16,676
the black holes
would be smaller.

281
00:14:16,677 --> 00:14:18,388
They haven't had
much time to grow.

282
00:14:18,398 --> 00:14:20,998
But now we've found
a 12-billion-solar-mass

283
00:14:20,999 --> 00:14:23,343
black hole that's actually less

284
00:14:23,344 --> 00:14:24,925
than a billion years
into the universe.

285
00:14:24,926 --> 00:14:26,775
How did this thing
form so early?

286
00:14:26,776 --> 00:14:28,328
How did it grow so fast?

287
00:14:28,329 --> 00:14:30,672
This is like walking
into a delivery room

288
00:14:30,673 --> 00:14:32,819
and finding a 100-pound baby.

289
00:14:32,820 --> 00:14:35,490
I mean, how does that
even happen?

290
00:14:35,491 --> 00:14:37,103
It doesn't make any sense.

291
00:14:37,113 --> 00:14:41,129
Physics tells us no black hole
could swallow enough stuff

292
00:14:41,139 --> 00:14:44,333
to get that big that quickly.

293
00:14:44,334 --> 00:14:46,708
There really wasn't enough
time between the big bang

294
00:14:46,718 --> 00:14:48,656
and when we're
studying these things

295
00:14:48,657 --> 00:14:51,130
for them to grow
to such large sizes

296
00:14:51,139 --> 00:14:53,710
just by eating
matter around them.

297
00:14:53,711 --> 00:14:57,599
So if there's not enough time

298
00:14:57,609 --> 00:15:01,831
maybe they're born supermassive.

299
00:15:01,832 --> 00:15:06,907
To understand how, we have
to travel back even farther,

300
00:15:06,917 --> 00:15:09,716
to not long after
the birth of the universe.

301
00:15:12,426 --> 00:15:14,464
The early universe
was definitely

302
00:15:14,474 --> 00:15:17,045
a much more compact

303
00:15:17,046 --> 00:15:18,627
and richer place for material.

304
00:15:18,628 --> 00:15:20,972
It was smaller,
and it was denser.

305
00:15:20,973 --> 00:15:22,950
Things were much closer.
It was hotter.

306
00:15:22,951 --> 00:15:28,331
It was just a much
more intense place to be.

307
00:15:28,332 --> 00:15:32,684
Clouds of hydrogen and
helium gas clumped together.

308
00:15:32,685 --> 00:15:35,958
As the clouds grew,
so did their gravity,

309
00:15:35,959 --> 00:15:39,451
sucking in more and more gas.

310
00:15:39,460 --> 00:15:41,132
Eventually, the ball of gas

311
00:15:41,142 --> 00:15:44,109
became so dense, it collapsed,

312
00:15:44,110 --> 00:15:48,036
triggering nuclear fusion.

313
00:15:48,037 --> 00:15:50,045
A star was born.

314
00:15:50,054 --> 00:15:52,625
These massive first stars

315
00:15:52,626 --> 00:15:56,256
are called population III stars.

316
00:15:56,257 --> 00:15:58,600
Because there was
so much food around,

317
00:15:58,601 --> 00:16:01,567
these stars were huge,

318
00:16:01,568 --> 00:16:05,791
many times bigger than
any stars that exist today.

319
00:16:05,792 --> 00:16:08,304
We think a lot of these
population III stars

320
00:16:08,305 --> 00:16:10,540
probably were
incredibly massive,

321
00:16:10,550 --> 00:16:13,714
incredibly short-lived,
and just blew up right away.

322
00:16:13,715 --> 00:16:17,108
They would've left massive
black holes behind.

323
00:16:28,167 --> 00:16:29,849
With so much food available,

324
00:16:29,859 --> 00:16:33,776
these young, ravenous
black holes, called quasars,

325
00:16:33,786 --> 00:16:36,219
started binge-eating

326
00:16:36,229 --> 00:16:39,097
and became incredibly bright.

327
00:16:39,098 --> 00:16:42,856
Billions of years later, we
can still see their gluttony.

328
00:16:44,835 --> 00:16:47,969
The most luminous,
bright objects in the universe

329
00:16:47,970 --> 00:16:49,423
are things called quasars.

330
00:16:49,424 --> 00:16:50,907
And it may seem kind of ironic.

331
00:16:50,908 --> 00:16:53,845
But what these really are
are supermassive black holes.

332
00:16:53,846 --> 00:16:55,824
There's so much stuff
trying to cram itself down

333
00:16:55,834 --> 00:16:59,356
the black hole that everything
gets very hot, very energetic.

334
00:16:59,366 --> 00:17:01,966
And you can see them
clear across the universe.

335
00:17:01,967 --> 00:17:04,934
But when we measured
the size of the young quasars,

336
00:17:04,935 --> 00:17:09,029
we discovered they were already
billions of solar masses.

337
00:17:09,030 --> 00:17:10,879
There's not enough time,

338
00:17:10,880 --> 00:17:13,322
a billion years after
the universe was created,

339
00:17:13,323 --> 00:17:16,754
for them to get to
a billion solar masses in...

340
00:17:16,755 --> 00:17:18,930
it's just too short a time.

341
00:17:18,931 --> 00:17:21,868
So the question becomes,

342
00:17:21,869 --> 00:17:25,035
that are this big
in that small amount of time?

343
00:17:25,044 --> 00:17:26,290
We need some other way

344
00:17:26,291 --> 00:17:28,733
of growing these
supermassive black holes.

345
00:17:28,734 --> 00:17:30,652
There needs to be
some other mechanism

346
00:17:30,653 --> 00:17:32,889
that allows them
to get that massive so early.

347
00:17:32,899 --> 00:17:35,766
But what is that?

348
00:17:35,767 --> 00:17:40,811
A clue can be found
in the very early universe.

349
00:17:40,812 --> 00:17:43,452
The early universe is still
so much of a mystery to us.

350
00:17:43,453 --> 00:17:45,431
We know that conditions
were very different.

351
00:17:45,441 --> 00:17:48,408
It was denser.
There was a lot more material.

352
00:17:48,409 --> 00:17:51,642
This period
is called the dark ages.

353
00:17:51,643 --> 00:17:53,423
During the dark age, we know

354
00:17:53,424 --> 00:17:56,223
that there was
basically nothing happening.

355
00:17:56,233 --> 00:17:57,577
Matter existed.

356
00:17:57,578 --> 00:17:59,595
We think that there
was hydrogen and helium gas

357
00:17:59,596 --> 00:18:02,464
but really not much else.

358
00:18:02,465 --> 00:18:04,442
There were a few stars around,

359
00:18:04,443 --> 00:18:07,746
but nothing large enough
to form giant black holes.

360
00:18:07,747 --> 00:18:10,615
But there were
huge clouds of gas.

361
00:18:10,616 --> 00:18:13,691
And because the universe
was much smaller and denser,

362
00:18:13,692 --> 00:18:17,321
the clouds were much thicker.

363
00:18:17,322 --> 00:18:20,585
The idea is that
from these basic ingredients,

364
00:18:20,586 --> 00:18:22,435
gravity and gas,

365
00:18:22,436 --> 00:18:26,461
the cosmos built
massive black holes.

366
00:18:26,462 --> 00:18:28,668
Somehow, the universe
has created a shortcut

367
00:18:28,678 --> 00:18:29,696
to the black hole.

368
00:18:29,697 --> 00:18:31,606
We've typically
thought of it as,

369
00:18:31,616 --> 00:18:33,821
cloud of gas
collapses into a star,

370
00:18:33,822 --> 00:18:37,322
star evolves, star dies,
leaves behind a black hole.

371
00:18:37,323 --> 00:18:38,935
Perhaps the universe
has found a way

372
00:18:38,936 --> 00:18:41,013
to skip the star phase

373
00:18:41,023 --> 00:18:42,902
and go directly
to the black hole.

374
00:18:46,038 --> 00:18:50,587
Clouds of gas may have
built massive black holes

375
00:18:50,588 --> 00:18:54,089
in a process
called direct collapse.

376
00:18:54,090 --> 00:18:56,888
As they collapsed,
they never even formed a star.

377
00:18:56,889 --> 00:18:59,865
They just collapsed straight
into a giant black hole.

378
00:18:59,866 --> 00:19:01,410
Through this direct
collapse theory,

379
00:19:01,419 --> 00:19:03,723
you can form really
big black holes.

380
00:19:03,724 --> 00:19:06,236
Imagine what it's like seeing
one of these giant clouds

381
00:19:06,237 --> 00:19:08,343
of gas collapsing down
into a black hole.

382
00:19:08,344 --> 00:19:10,262
You might think
you start with, okay,

383
00:19:10,263 --> 00:19:12,240
cloud of gas slowly collapsing,

384
00:19:12,241 --> 00:19:14,150
and, boop, it's a black hole.

385
00:19:14,160 --> 00:19:16,394
That wouldn't be the case.
It would be more like

386
00:19:16,395 --> 00:19:18,610
giant cloud of gas
starts collapsing,

387
00:19:18,611 --> 00:19:21,509
then... aah! Black hole.

388
00:19:21,519 --> 00:19:23,556
It's believed
that direct collapse

389
00:19:23,557 --> 00:19:25,436
could have created black holes

390
00:19:25,446 --> 00:19:28,215
up to a million times
the mass of the Sun,

391
00:19:28,216 --> 00:19:29,996
much bigger
than from the collapse

392
00:19:29,997 --> 00:19:31,677
of a single star.

393
00:19:31,678 --> 00:19:33,062
These early black holes

394
00:19:33,063 --> 00:19:35,338
are sort of like the galaxies
that never were.

395
00:19:35,348 --> 00:19:36,831
They were gonna make galaxies.

396
00:19:36,832 --> 00:19:40,126
But instead, they collapsed
into very massive black holes.

397
00:19:42,114 --> 00:19:44,714
For direct collapse
to form a black hole,

398
00:19:44,715 --> 00:19:47,919
the conditions need
to be precise.

399
00:19:47,920 --> 00:19:50,621
The clouds must be
very symmetrical,

400
00:19:50,631 --> 00:19:53,132
forming a smooth ball.

401
00:19:53,133 --> 00:19:55,941
If you have a ball of gas
that isn't quite a ball,

402
00:19:55,942 --> 00:19:57,683
that's not quite homogeneous,

403
00:19:57,693 --> 00:19:59,730
as it collapses, it'll fragment.

404
00:19:59,731 --> 00:20:02,074
And it'll fragment into objects
that won't form black holes.

405
00:20:02,075 --> 00:20:04,686
So you want it to be hot enough

406
00:20:04,687 --> 00:20:08,514
that it stays
one big, giant thing.

407
00:20:08,515 --> 00:20:10,325
But it does need to cool
a little bit, right,

408
00:20:10,335 --> 00:20:13,164
so that you get it
to collapse in on itself.

409
00:20:16,596 --> 00:20:20,326
You have to get
uniform collapse over time

410
00:20:20,335 --> 00:20:23,659
of a very large amount
of hydrogen gas, presumably,

411
00:20:23,669 --> 00:20:26,833
which is the original matter
in the universe,

412
00:20:26,834 --> 00:20:30,098
collapsing spherically
symmetrically,

413
00:20:30,099 --> 00:20:31,819
without fragmenting,

414
00:20:31,820 --> 00:20:35,509
over a period of less
than 500 million years.

415
00:20:41,227 --> 00:20:43,660
Direct collapse
may have created black holes

416
00:20:43,670 --> 00:20:46,172
a million times
the mass of the Sun.

417
00:20:46,173 --> 00:20:48,051
But it can't completely explain

418
00:20:48,052 --> 00:20:52,572
the 12 billion solar-mass
supermassive black holes

419
00:20:52,573 --> 00:20:55,252
we see in the early universe.

420
00:20:55,253 --> 00:20:59,536
Maybe gigantic supermassive
black holes were created

421
00:20:59,546 --> 00:21:02,572
by strange, unseen forces.

422
00:21:02,573 --> 00:21:04,452
Maybe they were created

423
00:21:04,462 --> 00:21:07,826
by the mysterious dark universe.

424
00:21:20,734 --> 00:21:24,858
Astronomers looking
deep into the early universe

425
00:21:24,859 --> 00:21:29,408
have discovered gigantic
supermassive black holes.

426
00:21:29,409 --> 00:21:31,120
This is a pretty deep mystery.

427
00:21:31,130 --> 00:21:33,168
There are these
supermassive black holes

428
00:21:33,178 --> 00:21:35,086
that exist
in the very early universe.

429
00:21:35,087 --> 00:21:38,054
And by all accounts,
they should not exist.

430
00:21:38,055 --> 00:21:40,725
According to
the normal laws of physics,

431
00:21:40,735 --> 00:21:42,050
it shouldn't have been possible

432
00:21:42,051 --> 00:21:45,017
for them to grow so big
so quickly.

433
00:21:45,018 --> 00:21:47,926
For astrophysicists,
understanding how black holes

434
00:21:47,927 --> 00:21:51,259
have grown to be so large is
one of our biggest mysteries.

435
00:21:51,260 --> 00:21:52,842
We need some other way

436
00:21:52,843 --> 00:21:54,889
of growing these
supermassive black holes.

437
00:21:54,890 --> 00:21:56,670
There needs to be
some other mechanism

438
00:21:56,671 --> 00:21:59,182
that allows them
to get that massive so early.

439
00:21:59,183 --> 00:22:01,626
But what is that?

440
00:22:01,627 --> 00:22:04,029
Everything we can see
in the night sky

441
00:22:04,030 --> 00:22:06,472
makes up just 4.8%

442
00:22:06,473 --> 00:22:09,183
of all the matter in the cosmos.

443
00:22:09,184 --> 00:22:11,458
The rest is the dark universe,

444
00:22:11,459 --> 00:22:13,764
including dark matter.

445
00:22:13,774 --> 00:22:18,056
We can't see it, feel it,
or detect it directly.

446
00:22:18,057 --> 00:22:20,697
But we know dark matter
is there.

447
00:22:20,698 --> 00:22:24,367
Its gravity is tugging
on everything around it.

448
00:22:24,368 --> 00:22:25,949
And we're beginning
to understand

449
00:22:25,950 --> 00:22:28,027
it plays a fundamental role

450
00:22:28,027 --> 00:22:30,499
in the formation
of the universe.

451
00:22:30,500 --> 00:22:32,874
Most of the stuff
that collects together

452
00:22:32,884 --> 00:22:34,763
gravitationally is dark matter.

453
00:22:34,764 --> 00:22:37,532
So perhaps black holes form

454
00:22:37,533 --> 00:22:40,432
somehow with the inclusion
of dark matter.

455
00:22:40,442 --> 00:22:42,251
One way of looking at it
is there's six times

456
00:22:42,252 --> 00:22:43,903
as much dark matter
as normal matter.

457
00:22:43,904 --> 00:22:46,346
So there's six times
as much food out there

458
00:22:46,347 --> 00:22:47,662
for the black holes to eat

459
00:22:47,663 --> 00:22:50,441
if they're able to tap
into this dark stuff.

460
00:22:50,442 --> 00:22:53,409
Maybe these supermassive
black holes are growing

461
00:22:53,410 --> 00:22:55,555
by eating dark matter.

462
00:22:55,556 --> 00:22:58,394
There are
some tantalizing clues.

463
00:22:58,395 --> 00:23:00,996
The largest supermassive
black holes

464
00:23:00,997 --> 00:23:04,003
don't live in the galaxies
with the most regular matter.

465
00:23:04,004 --> 00:23:07,801
They live in the galaxies
with the most dark matter.

466
00:23:07,802 --> 00:23:10,541
The one thing we know
about dark matter right now

467
00:23:10,542 --> 00:23:12,450
is that it has gravity.

468
00:23:12,451 --> 00:23:14,429
And a black hole runs
on gravity.

469
00:23:14,429 --> 00:23:16,051
It attracts anything with mass.

470
00:23:16,052 --> 00:23:17,900
So there's no reason to assume

471
00:23:17,901 --> 00:23:20,205
that black holes would
only eat regular matter.

472
00:23:20,206 --> 00:23:24,498
And now we know that there's far
more dark matter out there.

473
00:23:24,499 --> 00:23:29,513
Maybe dark matter
helps the black holes eat.

474
00:23:29,514 --> 00:23:31,987
Maybe in some ways,
dark matter is a feeder

475
00:23:31,997 --> 00:23:34,301
for these supermassive
black holes.

476
00:23:34,302 --> 00:23:37,170
Perhaps what really grows
a supermassive black hole

477
00:23:37,171 --> 00:23:40,246
is all of the regular matter
being directed into the center

478
00:23:40,247 --> 00:23:43,175
by the dark matter around it.

479
00:23:43,185 --> 00:23:46,082
Maybe the dark
matter's powerful gravity

480
00:23:46,083 --> 00:23:47,863
sucks in regular matter

481
00:23:47,873 --> 00:23:51,433
and funnels it
into the black hole.

482
00:23:51,434 --> 00:23:54,431
In a sense, the dark
matter is greasing the wheels.

483
00:23:54,432 --> 00:23:56,152
It's sort of tilting
the table up

484
00:23:56,153 --> 00:23:58,230
so that that food can
slide right in.

485
00:24:01,929 --> 00:24:04,866
But now scientists
think the dark matter

486
00:24:04,867 --> 00:24:08,755
may create gigantic
black holes directly

487
00:24:08,765 --> 00:24:13,047
by igniting dark stars.

488
00:24:13,048 --> 00:24:14,669
Some believe that dark matter

489
00:24:14,670 --> 00:24:17,369
sparked early universe
super stars.

490
00:24:17,370 --> 00:24:22,622
When they die, they leave behind
supermassive black holes.

491
00:24:22,623 --> 00:24:24,106
Dark stars sound like

492
00:24:24,107 --> 00:24:26,115
they come from
the fertile imagination

493
00:24:26,125 --> 00:24:28,162
of some Sci-Fi writer.

494
00:24:28,172 --> 00:24:31,199
But Dr. Katie Freese believes
they may explain

495
00:24:31,209 --> 00:24:36,520
how early supermassive
black holes grew so fast.

496
00:24:36,521 --> 00:24:37,934
Dark stars are amazing.

497
00:24:37,935 --> 00:24:40,308
So, when we first had this idea,

498
00:24:40,309 --> 00:24:41,595
we got excited really quickly,

499
00:24:41,605 --> 00:24:43,780
because this is
a new type of star

500
00:24:43,781 --> 00:24:46,975
that has never been seen before.

501
00:24:46,976 --> 00:24:49,715
Dark stars may have
been some of the first stars

502
00:24:49,716 --> 00:24:51,931
to form in the universe.

503
00:24:51,932 --> 00:24:53,444
They sparked into life

504
00:24:53,445 --> 00:24:57,274
when the universe was just
200 million years old.

505
00:24:57,283 --> 00:25:02,792
But how could dark stars form
really massive black holes?

506
00:25:02,793 --> 00:25:07,571
A newborn black hole can't weigh
more than its parent star.

507
00:25:07,581 --> 00:25:11,833
So in order to give birth to
a really massive black hole,

508
00:25:11,834 --> 00:25:16,284
the parent star has to be
supermassive, as well.

509
00:25:16,285 --> 00:25:18,827
These early objects
are really strange.

510
00:25:18,828 --> 00:25:20,973
They're very cool.

511
00:25:20,974 --> 00:25:23,387
And they're really, really big.

512
00:25:23,388 --> 00:25:26,780
The size of these things
is 10 times the distance

513
00:25:26,781 --> 00:25:29,362
between the Sun and the earth.

514
00:25:31,538 --> 00:25:34,041
But how is that possible?

515
00:25:34,051 --> 00:25:38,402
Regular stars have
an upper size limit.

516
00:25:38,403 --> 00:25:42,131
A star is a battle between
gravity pushing inwards

517
00:25:42,132 --> 00:25:44,378
and nuclear fusion pushing out.

518
00:25:47,781 --> 00:25:49,323
When the star grows too big,

519
00:25:49,324 --> 00:25:53,685
its gravity
becomes overwhelming.

520
00:25:53,686 --> 00:25:55,268
The delicate balance

521
00:25:55,269 --> 00:25:59,165
between gravity
and fusion is broken.

522
00:25:59,166 --> 00:26:04,012
Gravity wins out,
and the star collapses.

523
00:26:04,013 --> 00:26:06,851
But dark stars
may have a work-around

524
00:26:06,852 --> 00:26:11,075
that lets them
become supermassive.

525
00:26:11,076 --> 00:26:13,023
So, they are made
of ordinary matter.

526
00:26:13,024 --> 00:26:15,595
They're made
of hydrogen and helium.

527
00:26:15,596 --> 00:26:18,533
But they're powered
by dark matter.

528
00:26:18,534 --> 00:26:21,471
We don't know what
dark matter is made from.

529
00:26:21,472 --> 00:26:26,555
But we do have theories
on how it might power a star.

530
00:26:26,556 --> 00:26:29,127
One of the best ideas
we have for dark matter

531
00:26:29,128 --> 00:26:33,094
is that it's made of weakly
interacting massive particles,

532
00:26:33,095 --> 00:26:35,141
or wimps for short.

533
00:26:35,142 --> 00:26:37,515
So, these wimps are
their own antimatter.

534
00:26:37,516 --> 00:26:40,019
And that means, whenever
they encounter each other,

535
00:26:40,029 --> 00:26:43,816
they annihilate and turn
into something else.

536
00:26:43,817 --> 00:26:46,587
That means a lot of heat
is released, a lot of energy.

537
00:26:46,597 --> 00:26:49,891
And it's that energy
that could power stars.

538
00:26:52,799 --> 00:26:55,241
The energy
from the wimps' annihilations

539
00:26:55,242 --> 00:26:59,959
keeps the star from
collapsing like a normal star.

540
00:26:59,960 --> 00:27:02,235
So it's possible
that, in some stars,

541
00:27:02,236 --> 00:27:04,015
their internal reactions

542
00:27:04,016 --> 00:27:07,022
are actually being powered
by dark matter.

543
00:27:07,023 --> 00:27:09,891
If that's the case, then you
could imagine situations

544
00:27:09,892 --> 00:27:11,374
where, when that burns out,

545
00:27:11,375 --> 00:27:14,312
you produce very massive
black holes.

546
00:27:14,313 --> 00:27:15,935
So it could be that dark matter,

547
00:27:15,936 --> 00:27:17,319
the physics of dark matter,

548
00:27:17,320 --> 00:27:20,584
plays really important roles
in creating black holes

549
00:27:20,585 --> 00:27:23,097
and their prevalence
in the universe.

550
00:27:31,218 --> 00:27:33,454
The energy from the dark matter

551
00:27:33,464 --> 00:27:38,379
allows the dark stars
to grow huge.

552
00:27:38,380 --> 00:27:40,022
When they first form,
they're small.

553
00:27:40,032 --> 00:27:42,861
They're about the mass
of the Sun.

554
00:27:42,871 --> 00:27:44,878
But because they're so cool,

555
00:27:44,879 --> 00:27:46,164
they keep accumulating matter

556
00:27:46,165 --> 00:27:47,717
and growing, growing, growing.

557
00:27:47,718 --> 00:27:50,121
And some of them will get
to be a million times

558
00:27:50,131 --> 00:27:54,581
as massive as the Sun
and a billion times as bright.

559
00:27:54,582 --> 00:27:57,085
But these giants
don't live for long.

560
00:27:57,095 --> 00:27:59,468
Eventually,
the dark matter particles

561
00:27:59,469 --> 00:28:01,941
wipe each other out completely.

562
00:28:01,942 --> 00:28:03,425
And there is no more fuel

563
00:28:03,426 --> 00:28:05,967
to keep the massive amount
of ordinary matter

564
00:28:05,968 --> 00:28:08,479
from collapsing.

565
00:28:08,480 --> 00:28:09,894
And then that's it.

566
00:28:09,895 --> 00:28:12,505
There's nothing to sustain
this big, puffy object.

567
00:28:12,506 --> 00:28:17,352
If it's big enough, you collapse
directly to a black hole.

568
00:28:17,353 --> 00:28:21,912
A monster
supermassive black hole.

569
00:28:21,913 --> 00:28:24,217
It's really fun
to think about the possibility

570
00:28:24,218 --> 00:28:25,671
that the physics of dark matter

571
00:28:25,672 --> 00:28:28,045
is actually helping
to power stars.

572
00:28:28,046 --> 00:28:29,766
If so, it would bring, you know,

573
00:28:29,767 --> 00:28:32,171
a whole new window
into our understanding

574
00:28:32,181 --> 00:28:34,416
of stars and their evolution.

575
00:28:36,959 --> 00:28:41,478
At the moment, dark stars
are just theoretical.

576
00:28:41,479 --> 00:28:44,287
But when the powerful
James Webb telescope

577
00:28:44,288 --> 00:28:46,562
comes online in 2018,

578
00:28:46,563 --> 00:28:50,529
we may get our first glimpse.

579
00:28:50,530 --> 00:28:54,189
We're gonna do an observing
run and look f

580
00:28:54,190 --> 00:28:55,544
and so we're very excited.

581
00:28:55,545 --> 00:28:57,226
If you would find an entirely
new type of star,

582
00:28:57,227 --> 00:29:00,431
that would be huge.

583
00:29:00,432 --> 00:29:02,933
While Katie Freese
looks for dark stars,

584
00:29:02,934 --> 00:29:06,633
another team is investigating
another radical idea

585
00:29:06,634 --> 00:29:08,413
that offers new insight

586
00:29:08,414 --> 00:29:13,765
into how supermassive
black holes grow so huge.

587
00:29:13,766 --> 00:29:16,069
They detect the faint echoes

588
00:29:16,070 --> 00:29:20,135
of a violent event
from across the universe,

589
00:29:20,136 --> 00:29:23,567
the remnants of
an extraordinary collision,

590
00:29:23,568 --> 00:29:25,476
a supremely energetic event

591
00:29:25,477 --> 00:29:29,701
that reveals
black holes are cannibals.

592
00:29:44,192 --> 00:29:46,862
Our universe
is filled with enormous

593
00:29:46,863 --> 00:29:51,521
supermassive black holes
that defy explanation.

594
00:29:51,522 --> 00:29:53,430
Supermassive black holes
are one of the things

595
00:29:53,431 --> 00:29:55,478
in the universe that,
when you run the physics,

596
00:29:55,479 --> 00:29:57,723
when you run the math
of how did they evolve,

597
00:29:57,724 --> 00:29:59,771
they really shouldn't be there.

598
00:29:59,772 --> 00:30:02,738
It's still a profound mystery.

599
00:30:02,739 --> 00:30:04,718
The universe hasn't
been around long enough

600
00:30:04,728 --> 00:30:06,171
for regular black holes

601
00:30:06,172 --> 00:30:09,574
to eat enough matter
to get supermassive.

602
00:30:09,575 --> 00:30:11,583
So how did they get so big?

603
00:30:11,592 --> 00:30:12,976
The most logical answer

604
00:30:12,977 --> 00:30:16,112
is that large black holes
are born large,

605
00:30:16,113 --> 00:30:18,942
around 1 to 2 billion
solar masses.

606
00:30:18,952 --> 00:30:21,484
But that's still
over 10 times smaller

607
00:30:21,494 --> 00:30:25,915
than the largest supermassive
black holes out there.

608
00:30:25,916 --> 00:30:27,953
Given the time scales, it
doesn't seem to add up.

609
00:30:27,963 --> 00:30:29,604
We need some other way

610
00:30:29,605 --> 00:30:31,683
to make these
supermassive black holes.

611
00:30:31,692 --> 00:30:33,532
And the question is,
what is that?

612
00:30:35,817 --> 00:30:39,308
A clue came
from a large, isolated galaxy

613
00:30:39,309 --> 00:30:41,524
200 million light-years away

614
00:30:41,525 --> 00:30:43,800
in a quiet part of the universe.

615
00:30:45,719 --> 00:30:49,576
Nestling alone was
a supermassive black hole

616
00:30:49,577 --> 00:30:54,789
with a mass of 17 billion suns.

617
00:30:54,790 --> 00:30:56,411
Normally, such monsters

618
00:30:56,412 --> 00:30:59,210
are found in dense regions
of space

619
00:30:59,211 --> 00:31:03,671
with lots of galaxies
and lots of stars.

620
00:31:03,672 --> 00:31:06,075
This black holes doesn't match
its surroundings at all.

621
00:31:06,076 --> 00:31:08,320
It's kind of like driving
to the middle of a desert

622
00:31:08,321 --> 00:31:10,269
and coming across
the empire state building.

623
00:31:10,270 --> 00:31:12,979
Now, the empire state building
belongs in the middle of a city.

624
00:31:12,980 --> 00:31:14,524
And a black hole this big

625
00:31:14,533 --> 00:31:18,024
belongs in a rich cluster
of galaxies.

626
00:31:18,025 --> 00:31:20,764
This is the first time
astronomers have found

627
00:31:20,765 --> 00:31:22,347
such a giant object

628
00:31:22,348 --> 00:31:26,571
lurking in such a relatively
empty area of the universe.

629
00:31:26,572 --> 00:31:28,094
So you got to ask the question,

630
00:31:28,095 --> 00:31:30,993
if there's nothing else around,
how exactly do you grow

631
00:31:31,003 --> 00:31:33,535
a 17-billion-solar-mass
black hole?

632
00:31:36,711 --> 00:31:40,142
One possible answer
is the stuff of nightmares.

633
00:31:40,143 --> 00:31:42,190
Maybe the story
of this black hole

634
00:31:42,191 --> 00:31:44,494
is actually a little more
scary than we thought.

635
00:31:44,495 --> 00:31:45,681
Maybe it's all alone

636
00:31:45,682 --> 00:31:47,957
because it ate
all of its neighbors.

637
00:31:50,341 --> 00:31:53,575
Maybe it was eating
more than galaxies.

638
00:31:53,576 --> 00:31:56,939
Maybe it was eating
its own kind.

639
00:31:58,819 --> 00:32:00,995
The thing about black holes
is they're omnivores.

640
00:32:01,005 --> 00:32:02,418
They'll eat anything.

641
00:32:02,419 --> 00:32:04,792
Anything that gets close them,
they'll gobble up.

642
00:32:04,793 --> 00:32:06,772
One way black holes
can grow so large

643
00:32:06,781 --> 00:32:08,393
is by eating other black holes.

644
00:32:08,394 --> 00:32:11,193
So in a sense,
they may be cannibals.

645
00:32:11,203 --> 00:32:14,694
Cannibal black holes
were just theoretical.

646
00:32:14,695 --> 00:32:17,563
We'd never actually
seen them eat each other.

647
00:32:19,720 --> 00:32:23,478
Then scientists detected
the faint echoes

648
00:32:23,479 --> 00:32:27,108
of actual ripples
in space-time.

649
00:32:27,109 --> 00:32:28,661
When engineers turned on

650
00:32:28,662 --> 00:32:32,815
the laser interferometer
gravitational-wave observatory,

651
00:32:32,816 --> 00:32:34,833
or LIGO for short,

652
00:32:34,834 --> 00:32:36,713
they immediately picked up

653
00:32:36,714 --> 00:32:40,472
the faint signal
of gravitational waves.

654
00:32:40,473 --> 00:32:42,222
Gravitational waves are created

655
00:32:42,223 --> 00:32:45,033
by huge explosions in space.

656
00:32:48,228 --> 00:32:52,915
To make them, you need an almost
unimaginably energetic event,

657
00:32:52,916 --> 00:32:55,627
something really, really big...

658
00:32:57,833 --> 00:33:01,997
...something like
merging black holes.

659
00:33:03,906 --> 00:33:06,181
A black hole merger
is the most violent,

660
00:33:06,191 --> 00:33:07,467
the most energetic thing

661
00:33:07,477 --> 00:33:09,712
that happens
in the universe, period.

662
00:33:12,561 --> 00:33:16,478
Picture the scene,
1.3 billion years ago.

663
00:33:16,488 --> 00:33:20,543
Two black holes circle each
other in a dance of death.

664
00:33:20,544 --> 00:33:24,302
The larger black hole
pulls the smaller one inwards

665
00:33:24,303 --> 00:33:27,734
until they're locked together
in a spiral.

666
00:33:27,735 --> 00:33:30,177
Very, very slowly,
that orbit is decaying.

667
00:33:30,178 --> 00:33:32,256
They're getting closer
and closer and closer.

668
00:33:32,266 --> 00:33:35,688
And then they will merge
into one giant black hole,

669
00:33:35,698 --> 00:33:39,485
truly one of the most dramatic
events in the universe.

670
00:33:39,486 --> 00:33:41,533
Finally, they collide

671
00:33:41,534 --> 00:33:45,263
in one of the largest bangs
since the big bang.

672
00:33:48,468 --> 00:33:50,376
I would have loved
to have been able

673
00:33:50,377 --> 00:33:52,158
to safely view the collision

674
00:33:52,168 --> 00:33:54,274
of these two
black holes up close.

675
00:33:54,275 --> 00:33:55,560
Imagine these two black holes

676
00:33:55,561 --> 00:33:57,439
as they spiral
in toward each other,

677
00:33:57,440 --> 00:33:59,616
going faster and faster
and faster and faster.

678
00:33:59,626 --> 00:34:02,158
And then, suddenly, where
there appears to be nothing

679
00:34:02,168 --> 00:34:04,640
or just distortions in space
in front of you,

680
00:34:04,641 --> 00:34:07,904
suddenly, there is this
enormous burst of energy.

681
00:34:07,905 --> 00:34:11,040
And everything
just rains around you.

682
00:34:11,041 --> 00:34:14,403
By measuring the frequency

683
00:34:14,404 --> 00:34:18,628
we can calculate the size
of the objects causing them.

684
00:34:18,638 --> 00:34:20,378
When those two black holes,

685
00:34:20,379 --> 00:34:22,920
weighing 29 solar masses

686
00:34:22,921 --> 00:34:26,649
and 36 solar masses, collided,

687
00:34:26,650 --> 00:34:30,716
they created a black hole
around twice the size.

688
00:34:32,724 --> 00:34:35,235
In some ways,
it's very elegant and simple.

689
00:34:35,236 --> 00:34:37,411
You take two black holes.
You spiral them in together.

690
00:34:37,412 --> 00:34:40,380
And you end up
with one big black hole.

691
00:34:42,497 --> 00:34:45,928
The event showed that black
holes can double their mass

692
00:34:45,929 --> 00:34:49,588
through cannibalism... Almost.

693
00:34:49,589 --> 00:34:54,247
The final black hole was less
than the sum of its parts.

694
00:34:54,248 --> 00:34:57,511
There were 3 solar masses
missing.

695
00:34:57,512 --> 00:34:59,687
That may not sound like a lot.

696
00:34:59,688 --> 00:35:02,260
So let's put it in context.

697
00:35:02,270 --> 00:35:04,445
Our sun is burning

698
00:35:04,446 --> 00:35:07,344
about 100 billion
hydrogen bombs every second.

699
00:35:07,345 --> 00:35:09,323
And over its
10-billion-year lifetime,

700
00:35:09,333 --> 00:35:11,805
it will convert less
than maybe 1% of the mass

701
00:35:11,806 --> 00:35:12,992
of the Sun to energy.

702
00:35:12,993 --> 00:35:15,168
In 2/10 of a second,

703
00:35:15,169 --> 00:35:17,939
3 times the mass
of the Sun in matter

704
00:35:17,949 --> 00:35:20,580
got converted to energy
in that collision.

705
00:35:22,499 --> 00:35:26,395
It was 36 septillion yottawatts.

706
00:35:26,396 --> 00:35:28,928
What does that mean?
A lot of freaking energy.

707
00:35:28,938 --> 00:35:32,132
That's more energy
in that 2/10 of a second

708
00:35:32,133 --> 00:35:34,249
than is emitted by all the stars

709
00:35:34,250 --> 00:35:36,298
in the visible universe
in the same time.

710
00:35:38,840 --> 00:35:42,203
In its first run,
LIGO detected two collisions.

711
00:35:44,320 --> 00:35:46,426
This suggests
that cannibal black holes

712
00:35:46,427 --> 00:35:48,107
are relatively common

713
00:35:48,108 --> 00:35:52,232
and that each feast
builds a larger black hole.

714
00:35:52,233 --> 00:35:54,547
But so far,
the largest black hole

715
00:35:54,548 --> 00:35:56,327
these mergers have produced

716
00:35:56,328 --> 00:35:58,771
is 62 solar masses,

717
00:35:58,772 --> 00:36:03,915
not close to the largest
supermassives we've found.

718
00:36:03,925 --> 00:36:06,100
It's hard to imagine,
in 13.8 billion years,

719
00:36:06,101 --> 00:36:08,969
that there'd be enough
collisions of 30-solar-mass

720
00:36:08,970 --> 00:36:13,262
black holes to build up to form a
billion-solar-mass black hole.

721
00:36:13,263 --> 00:36:16,200
That's 100 million collisions.

722
00:36:16,201 --> 00:36:19,830
So maybe small
black holes eating each other

723
00:36:19,831 --> 00:36:21,413
isn't the solution.

724
00:36:21,414 --> 00:36:24,609
Maybe supermassive black holes

725
00:36:24,619 --> 00:36:27,516
are eating each other.

726
00:36:27,517 --> 00:36:30,325
If so, could
the supermassive black hole

727
00:36:30,326 --> 00:36:34,550
at the heart of our own galaxy
be on the menu?

728
00:36:49,071 --> 00:36:51,513
We've found
supermassive black holes

729
00:36:51,514 --> 00:36:55,303
so large, they defy explanation.

730
00:36:55,313 --> 00:36:56,696
They're too big to have grown

731
00:36:56,697 --> 00:37:00,920
by simply eating
the matter around them.

732
00:37:00,921 --> 00:37:04,413
They can't form the same way
that regular black holes do.

733
00:37:04,423 --> 00:37:07,054
There must be something else
that happens that lets them grow

734
00:37:07,064 --> 00:37:09,862
to such enormous mass.

735
00:37:09,863 --> 00:37:12,701
Too large to have
grown from dark stars

736
00:37:12,702 --> 00:37:16,500
and too big to have grown
from regular black holes

737
00:37:16,501 --> 00:37:18,804
simply eating each other.

738
00:37:18,805 --> 00:37:21,179
Merging black holes
almost certainly play a role

739
00:37:21,189 --> 00:37:24,018
in our understanding
of supermassive black holes.

740
00:37:24,028 --> 00:37:27,222
We think that supermassive black
holes themselves also merge

741
00:37:27,223 --> 00:37:30,259
and have merged regularly over
the course of the universe.

742
00:37:30,260 --> 00:37:32,208
Now, whether this
merging activity itself

743
00:37:32,209 --> 00:37:34,285
is enough to make them that big,

744
00:37:34,286 --> 00:37:36,660
the jury is still out on that.

745
00:37:36,670 --> 00:37:39,765
Now a newly discovered
type of galaxy

746
00:37:39,766 --> 00:37:42,109
may provide an answer.

747
00:37:42,110 --> 00:37:47,916
It's called w2246-0526.

748
00:37:47,917 --> 00:37:49,439
And we can't see it.

749
00:37:49,440 --> 00:37:52,970
But we can detect
the heat it gives off.

750
00:37:52,971 --> 00:37:55,077
This galaxy is an example

751
00:37:55,078 --> 00:37:59,202
of a rare class
of objects called hot dogs.

752
00:37:59,203 --> 00:38:01,843
One of the funnier terms f

753
00:38:01,844 --> 00:38:03,427
is a hot dog galaxy.

754
00:38:03,437 --> 00:38:05,711
And no, this is not
some delicious sausage snack.

755
00:38:05,712 --> 00:38:09,935
In fact, it means "hot,
dust-obscured galaxy."

756
00:38:09,936 --> 00:38:12,477
It's called obscured
because it's shrouded

757
00:38:12,478 --> 00:38:16,662
in so much dust and gas,
the only light that escapes

758
00:38:16,672 --> 00:38:21,221
is infrared in the form of heat.

759
00:38:21,222 --> 00:38:23,071
All this heat must be
coming from somewhere.

760
00:38:23,072 --> 00:38:25,841
So in the core,
there is a cauldron,

761
00:38:25,842 --> 00:38:27,751
a seething
supermassive black hole,

762
00:38:27,761 --> 00:38:29,600
the likes of which
we can't even imagine.

763
00:38:32,776 --> 00:38:34,882
Of all the supermassive
black holes we know of,

764
00:38:34,883 --> 00:38:37,325
the ones that are obscured
in these hot dog galaxies

765
00:38:37,326 --> 00:38:39,372
may be the ones
that are the most ravenous,

766
00:38:39,373 --> 00:38:40,955
consuming many millions of times

767
00:38:40,956 --> 00:38:43,924
the mass of the Sun.

768
00:38:43,933 --> 00:38:46,306
Scientists theorize
that hot dogs

769
00:38:46,307 --> 00:38:48,512
could be the offspring

770
00:38:48,513 --> 00:38:52,044
of cannibal giant black holes.

771
00:38:52,045 --> 00:38:54,122
When the monstrous
black holes merge,

772
00:38:54,132 --> 00:38:57,098
they drag gas and dust
with them.

773
00:38:57,099 --> 00:38:59,641
This brings more food
to the table,

774
00:38:59,641 --> 00:39:03,597
allowing the new black hole
to gorge itself.

775
00:39:03,598 --> 00:39:06,269
When you have these
two galaxies merging,

776
00:39:06,279 --> 00:39:09,146
they have all-new food.

777
00:39:09,147 --> 00:39:10,235
It's a brand-new dinner plate,

778
00:39:10,236 --> 00:39:14,132
a brand-new buffet
of food to eat.

779
00:39:14,133 --> 00:39:17,327
The combination
of cannibalism and fresh food

780
00:39:17,328 --> 00:39:20,394
allows the black holes
to grow super large.

781
00:39:22,907 --> 00:39:25,913
Perhaps this is how
the supermassive black hole

782
00:39:25,914 --> 00:39:27,624
at the center of our galaxy

783
00:39:27,625 --> 00:39:30,265
grew when it was young.

784
00:39:30,266 --> 00:39:31,849
But what's the future

785
00:39:31,859 --> 00:39:36,635
of our supermassive
Sagittarius "a" -star?

786
00:39:36,636 --> 00:39:38,683
As far as
supermassive black holes go,

787
00:39:38,684 --> 00:39:40,038
Sagittarius "a" -star

788
00:39:40,039 --> 00:39:41,948
is actually still kind of
in the minor leagues.

789
00:39:41,958 --> 00:39:44,292
It's small.
But it's not done yet.

790
00:39:44,293 --> 00:39:48,258
It's still eating.
It's still growing.

791
00:39:48,259 --> 00:39:50,504
And in around 4 billion years,

792
00:39:50,505 --> 00:39:55,351
it's going to become
25 times larger,

793
00:39:55,352 --> 00:39:59,249
because it's going to be
eaten by its neighbor.

794
00:40:04,066 --> 00:40:07,666
The giant Andromeda galaxy
is heading our way.

795
00:40:07,667 --> 00:40:11,098
And it's going to engulf
our milky way.

796
00:40:11,099 --> 00:40:12,543
When galaxies merge,

797
00:40:12,553 --> 00:40:16,608
their central supermassive
black holes merge.

798
00:40:16,609 --> 00:40:19,645
Andromeda's huge
supermassive black hole

799
00:40:19,646 --> 00:40:23,137
will drag Sagittarius "a" -star
into orbit...

800
00:40:25,323 --> 00:40:29,151
...gradually drawing it closer
and closer

801
00:40:29,152 --> 00:40:30,764
until it devours it.

802
00:40:33,741 --> 00:40:36,045
The new supermassive
black hole will weigh

803
00:40:36,046 --> 00:40:39,607
around 100 million solar masses.

804
00:40:39,617 --> 00:40:42,089
But the disruption
to the new galaxy

805
00:40:42,090 --> 00:40:45,384
will provide the new
supermassive black hole

806
00:40:45,394 --> 00:40:46,738
with plenty to eat

807
00:40:46,739 --> 00:40:50,241
and the opportunity to grow
a whole lot bigger.

808
00:40:52,882 --> 00:40:54,890
At present,
there are many theories

809
00:40:54,900 --> 00:40:59,083
of how supermassive
black holes get so big.

810
00:40:59,084 --> 00:41:02,744
Most likely, it's a
combination of them all.

811
00:41:02,754 --> 00:41:06,838
But however it happens,
we can be pretty sure

812
00:41:06,839 --> 00:41:11,398
it's one of the most spectacular
things in the universe.

813
00:41:11,399 --> 00:41:13,475
The jury's still out on exactly

814
00:41:13,476 --> 00:41:16,612
how supermassive black holes
become so massive.

815
00:41:19,876 --> 00:41:21,558
Making all
the black holes we see

816
00:41:21,568 --> 00:41:24,397
probably requires
a pretty diverse cookbook.

817
00:41:24,407 --> 00:41:26,681
So any physicist who's looking
for a really simple,

818
00:41:26,682 --> 00:41:28,887
single answer
for how they get made,

819
00:41:28,888 --> 00:41:32,220
they're probably
gonna be disappointed.

820
00:41:32,221 --> 00:41:35,060
It's probably a pretty complex
thing that's going on.

821
00:41:38,789 --> 00:41:41,993
It could be through eating.

822
00:41:41,994 --> 00:41:43,309
It could be through
eating and merging.

823
00:41:43,310 --> 00:41:45,752
And usually, the answer
is somewhere in the middle.

824
00:41:45,753 --> 00:41:48,096
So they will merge
with other black holes.

825
00:41:48,097 --> 00:41:51,362
And they'll also have
a few snacks between mergers.