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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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...Captions by Vitac...
www.Vitac.Com

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Captions paid for by
Discovery communications

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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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00:12:05,780 --> 00:12:07,728
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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00:12:25,810 --> 00:12:28,778
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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00:12:31,389 --> 00:12:34,851
weighing billions
of solar masses?

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Could that black hole
become so obese by eating?

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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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00:12:46,108 --> 00:12:48,916
When you think about it, if
you imagine an average galaxy

258
00:12:48,917 --> 00:12:50,895
has 100 billion stars,

259
00:12:50,896 --> 00:12:52,607
the black hole
would have to eat one

260
00:12:52,617 --> 00:12:55,188
in every five stars
in the galaxy.

261
00:12:55,189 --> 00:12:57,859
The universe is old.
But is it really old enough

262
00:12:57,860 --> 00:13:01,717
that black holes have had time
to consume billions of stars?

263
00:13:01,727 --> 00:13:03,705
That seems kind of unlikely.

264
00:13:03,706 --> 00:13:05,416
It doesn't seem to add up.

265
00:13:05,417 --> 00:13:06,939
We need some other way

266
00:13:06,940 --> 00:13:08,918
to make these
supermassive black holes.

267
00:13:08,919 --> 00:13:12,015
And the question is,
what is that?

268
00:13:12,025 --> 00:13:14,656
Maybe we've been making
this all too complicated.

269
00:13:14,666 --> 00:13:19,275
Maybe to get a big black hole is
to start big in the first place.

270
00:13:19,285 --> 00:13:22,708
So how can black
holes start big?

271
00:13:22,717 --> 00:13:26,080
To answer that question,
scientists had to journey back

272
00:13:26,081 --> 00:13:28,622
to the very start
of the universe,

273
00:13:28,623 --> 00:13:32,154
to a mysterious time
called the dark ages.

274
00:13:51,492 --> 00:13:53,905
As we look out
into the universe,

275
00:13:53,906 --> 00:13:58,426
we're seeing farther
and farther back in time.

276
00:13:58,427 --> 00:13:59,711
We have now looked back

277
00:13:59,712 --> 00:14:02,817
over 12 billion years

278
00:14:02,818 --> 00:14:06,250
to the time when the cosmos
was still an infant.

279
00:14:06,251 --> 00:14:11,492
And what we found
was a huge surprise.

280
00:14:11,493 --> 00:14:13,075
We had made the assumption

281
00:14:13,076 --> 00:14:15,351
that as you look farther
out into the universe,

282
00:14:15,361 --> 00:14:16,676
the black holes
would be smaller.

283
00:14:16,677 --> 00:14:18,388
They haven't had
much time to grow.

284
00:14:18,398 --> 00:14:20,998
But now we've found
a 12-billion-solar-mass

285
00:14:20,999 --> 00:14:23,343
black hole that's actually less

286
00:14:23,344 --> 00:14:24,925
than a billion years
into the universe.

287
00:14:24,926 --> 00:14:26,775
How did this thing
form so early?

288
00:14:26,776 --> 00:14:28,328
How did it grow so fast?

289
00:14:28,329 --> 00:14:30,672
This is like walking
into a delivery room

290
00:14:30,673 --> 00:14:32,819
and finding a 100-pound baby.

291
00:14:32,820 --> 00:14:35,490
I mean, how does that
even happen?

292
00:14:35,491 --> 00:14:37,103
It doesn't make any sense.

293
00:14:37,113 --> 00:14:41,129
Physics tells us no black hole
could swallow enough stuff

294
00:14:41,139 --> 00:14:44,333
to get that big that quickly.

295
00:14:44,334 --> 00:14:46,708
There really wasn't enough
time between the big bang

296
00:14:46,718 --> 00:14:48,656
and when we're
studying these things

297
00:14:48,657 --> 00:14:51,130
for them to grow
to such large sizes

298
00:14:51,139 --> 00:14:53,710
just by eating
matter around them.

299
00:14:53,711 --> 00:14:57,599
So if there's not enough time

300
00:14:57,609 --> 00:15:01,831
maybe they're born supermassive.

301
00:15:01,832 --> 00:15:06,907
To understand how, we have
to travel back even farther,

302
00:15:06,917 --> 00:15:09,716
to not long after
the birth of the universe.

303
00:15:12,426 --> 00:15:14,464
The early universe
was definitely

304
00:15:14,474 --> 00:15:17,045
a much more compact

305
00:15:17,046 --> 00:15:18,627
and richer place for material.

306
00:15:18,628 --> 00:15:20,972
It was smaller,
and it was denser.

307
00:15:20,973 --> 00:15:22,950
Things were much closer.
It was hotter.

308
00:15:22,951 --> 00:15:28,331
It was just a much
more intense place to be.

309
00:15:28,332 --> 00:15:32,684
Clouds of hydrogen and
helium gas clumped together.

310
00:15:32,685 --> 00:15:35,958
As the clouds grew,
so did their gravity,

311
00:15:35,959 --> 00:15:39,451
sucking in more and more gas.

312
00:15:39,460 --> 00:15:41,132
Eventually, the ball of gas

313
00:15:41,142 --> 00:15:44,109
became so dense, it collapsed,

314
00:15:44,110 --> 00:15:48,036
triggering nuclear fusion.

315
00:15:48,037 --> 00:15:50,045
A star was born.

316
00:15:50,054 --> 00:15:52,625
These massive first stars

317
00:15:52,626 --> 00:15:56,256
are called population III stars.

318
00:15:56,257 --> 00:15:58,600
Because there was
so much food around,

319
00:15:58,601 --> 00:16:01,567
these stars were huge,

320
00:16:01,568 --> 00:16:05,791
many times bigger than
any stars that exist today.

321
00:16:05,792 --> 00:16:08,304
We think a lot of these
population III stars

322
00:16:08,305 --> 00:16:10,540
probably were
incredibly massive,

323
00:16:10,550 --> 00:16:13,714
incredibly short-lived,
and just blew up right away.

324
00:16:13,715 --> 00:16:17,108
They would've left massive
black holes behind.

325
00:16:28,167 --> 00:16:29,849
With so much food available,

326
00:16:29,859 --> 00:16:33,776
these young, ravenous
black holes, called quasars,

327
00:16:33,786 --> 00:16:36,219
started binge-eating

328
00:16:36,229 --> 00:16:39,097
and became incredibly bright.

329
00:16:39,098 --> 00:16:42,856
Billions of years later, we
can still see their gluttony.

330
00:16:44,835 --> 00:16:47,969
The most luminous,
bright objects in the universe

331
00:16:47,970 --> 00:16:49,423
are things called quasars.

332
00:16:49,424 --> 00:16:50,907
And it may seem kind of ironic.

333
00:16:50,908 --> 00:16:53,845
But what these really are
are supermassive black holes.

334
00:16:53,846 --> 00:16:55,824
There's so much stuff
trying to cram itself down

335
00:16:55,834 --> 00:16:59,356
the black hole that everything
gets very hot, very energetic.

336
00:16:59,366 --> 00:17:01,966
And you can see them
clear across the universe.

337
00:17:01,967 --> 00:17:04,934
But when we measured
the size of the young quasars,

338
00:17:04,935 --> 00:17:09,029
we discovered they were already
billions of solar masses.

339
00:17:09,030 --> 00:17:10,879
There's not enough time,

340
00:17:10,880 --> 00:17:13,322
a billion years after
the universe was created,

341
00:17:13,323 --> 00:17:16,754
for them to get to
a billion solar masses in...

342
00:17:16,755 --> 00:17:18,930
it's just too short a time.

343
00:17:20,000 --> 00:17:22,937
So the question becomes,

344
00:17:22,938 --> 00:17:26,104
that are this big
in that small amount of time?

345
00:17:26,113 --> 00:17:27,359
We need some other way

346
00:17:27,360 --> 00:17:29,802
of growing these
supermassive black holes.

347
00:17:29,803 --> 00:17:31,721
There needs to be
some other mechanism

348
00:17:31,722 --> 00:17:33,958
that allows them
to get that massive so early.

349
00:17:33,968 --> 00:17:36,835
But what is that?

350
00:17:36,836 --> 00:17:41,880
A clue can be found
in the very early universe.

351
00:17:41,881 --> 00:17:44,521
The early universe is still
so much of a mystery to us.

352
00:17:44,522 --> 00:17:46,500
We know that conditions
were very different.

353
00:17:46,510 --> 00:17:49,477
It was denser.
There was a lot more material.

354
00:17:49,478 --> 00:17:52,711
This period
is called the dark ages.

355
00:17:52,712 --> 00:17:54,492
During the dark age, we know

356
00:17:54,493 --> 00:17:57,292
that there was
basically nothing happening.

357
00:17:57,302 --> 00:17:58,646
Matter existed.

358
00:17:58,647 --> 00:18:00,664
We think that there
was hydrogen and helium gas

359
00:18:00,665 --> 00:18:03,533
but really not much else.

360
00:18:03,534 --> 00:18:05,511
There were a few stars around,

361
00:18:05,512 --> 00:18:08,815
but nothing large enough
to form giant black holes.

362
00:18:08,816 --> 00:18:11,684
But there were
huge clouds of gas.

363
00:18:11,685 --> 00:18:14,760
And because the universe
was much smaller and denser,

364
00:18:14,761 --> 00:18:18,390
the clouds were much thicker.

365
00:18:18,391 --> 00:18:21,654
The idea is that
from these basic ingredients,

366
00:18:21,655 --> 00:18:23,504
gravity and gas,

367
00:18:23,505 --> 00:18:27,530
the cosmos built
massive black holes.

368
00:18:27,531 --> 00:18:29,737
Somehow, the universe
has created a shortcut

369
00:18:29,747 --> 00:18:30,765
to the black hole.

370
00:18:30,766 --> 00:18:32,675
We've typically
thought of it as,

371
00:18:32,685 --> 00:18:34,890
cloud of gas
collapses into a star,

372
00:18:34,891 --> 00:18:38,391
star evolves, star dies,
leaves behind a black hole.

373
00:18:38,392 --> 00:18:40,004
Perhaps the universe
has found a way

374
00:18:40,005 --> 00:18:42,082
to skip the star phase

375
00:18:42,092 --> 00:18:43,971
and go directly
to the black hole.

376
00:18:47,107 --> 00:18:51,656
Clouds of gas may have
built massive black holes

377
00:18:51,657 --> 00:18:55,158
in a process
called direct collapse.

378
00:18:55,159 --> 00:18:57,957
As they collapsed,
they never even formed a star.

379
00:18:57,958 --> 00:19:00,934
They just collapsed straight
into a giant black hole.

380
00:19:00,935 --> 00:19:02,479
Through this direct
collapse theory,

381
00:19:02,488 --> 00:19:04,792
you can form really
big black holes.

382
00:19:04,793 --> 00:19:07,305
Imagine what it's like seeing
one of these giant clouds

383
00:19:07,306 --> 00:19:09,412
of gas collapsing down
into a black hole.

384
00:19:09,413 --> 00:19:11,331
You might think
you start with, okay,

385
00:19:11,332 --> 00:19:13,309
cloud of gas slowly collapsing,

386
00:19:13,310 --> 00:19:15,219
and, boop, it's a black hole.

387
00:19:15,229 --> 00:19:17,463
That wouldn't be the case.
It would be more like

388
00:19:17,464 --> 00:19:19,679
giant cloud of gas
starts collapsing,

389
00:19:19,680 --> 00:19:22,578
then... aah! Black hole.

390
00:19:23,700 --> 00:19:25,737
It's believed
that direct collapse

391
00:19:25,738 --> 00:19:27,617
could have created black holes

392
00:19:27,627 --> 00:19:30,396
up to a million times
the mass of the Sun,

393
00:19:30,397 --> 00:19:32,177
much bigger
than from the collapse

394
00:19:32,178 --> 00:19:33,858
of a single star.

395
00:19:33,859 --> 00:19:35,243
These early black holes

396
00:19:35,244 --> 00:19:37,519
are sort of like the galaxies
that never were.

397
00:19:37,529 --> 00:19:39,012
They were gonna make galaxies.

398
00:19:39,013 --> 00:19:42,307
But instead, they collapsed
into very massive black holes.

399
00:19:44,295 --> 00:19:46,895
For direct collapse
to form a black hole,

400
00:19:46,896 --> 00:19:50,100
the conditions need
to be precise.

401
00:19:50,101 --> 00:19:52,802
The clouds must be
very symmetrical,

402
00:19:52,812 --> 00:19:55,313
forming a smooth ball.

403
00:19:55,314 --> 00:19:58,122
If you have a ball of gas
that isn't quite a ball,

404
00:19:58,123 --> 00:19:59,864
that's not quite homogeneous,

405
00:19:59,874 --> 00:20:01,911
as it collapses, it'll fragment.

406
00:20:01,912 --> 00:20:04,255
And it'll fragment into objects
that won't form black holes.

407
00:20:04,256 --> 00:20:06,867
So you want it to be hot enough

408
00:20:06,868 --> 00:20:10,695
that it stays
one big, giant thing.

409
00:20:10,696 --> 00:20:12,506
But it does need to cool
a little bit, right,

410
00:20:12,516 --> 00:20:15,345
so that you get it
to collapse in on itself.

411
00:20:18,777 --> 00:20:22,507
You have to get
uniform collapse over time

412
00:20:22,516 --> 00:20:25,840
of a very large amount
of hydrogen gas, presumably,

413
00:20:25,850 --> 00:20:29,014
which is the original matter
in the universe,

414
00:20:29,015 --> 00:20:32,279
collapsing spherically
symmetrically,

415
00:20:32,280 --> 00:20:34,000
without fragmenting,

416
00:20:34,001 --> 00:20:37,690
over a period of less
than 500 million years.

417
00:20:43,408 --> 00:20:45,841
Direct collapse
may have created black holes

418
00:20:45,851 --> 00:20:48,353
a million times
the mass of the Sun.

419
00:20:48,354 --> 00:20:50,232
But it can't completely explain

420
00:20:50,233 --> 00:20:54,753
the 12 billion solar-mass
supermassive black holes

421
00:20:54,754 --> 00:20:57,433
we see in the early universe.

422
00:20:57,434 --> 00:21:01,717
Maybe gigantic supermassive
black holes were created

423
00:21:01,727 --> 00:21:04,753
by strange, unseen forces.

424
00:21:04,754 --> 00:21:06,633
Maybe they were created

425
00:21:06,643 --> 00:21:10,007
by the mysterious dark universe.

426
00:21:22,915 --> 00:21:27,039
Astronomers looking
deep into the early universe

427
00:21:27,040 --> 00:21:31,589
have discovered gigantic
supermassive black holes.

428
00:21:31,590 --> 00:21:33,301
This is a pretty deep mystery.

429
00:21:33,311 --> 00:21:35,349
There are these
supermassive black holes

430
00:21:35,359 --> 00:21:37,267
that exist
in the very early universe.

431
00:21:37,268 --> 00:21:40,235
And by all accounts,
they should not exist.

432
00:21:40,236 --> 00:21:42,906
According to
the normal laws of physics,

433
00:21:42,916 --> 00:21:44,231
it shouldn't have been possible

434
00:21:44,232 --> 00:21:47,198
for them to grow so big
so quickly.

435
00:21:47,199 --> 00:21:50,107
For astrophysicists,
understanding how black holes

436
00:21:50,108 --> 00:21:53,440
have grown to be so large is
one of our biggest mysteries.

437
00:21:53,441 --> 00:21:55,023
We need some other way

438
00:21:55,024 --> 00:21:57,070
of growing these
supermassive black holes.

439
00:21:57,071 --> 00:21:58,851
There needs to be
some other mechanism

440
00:21:58,852 --> 00:22:01,363
that allows them
to get that massive so early.

441
00:22:01,364 --> 00:22:03,807
But what is that?

442
00:22:03,808 --> 00:22:06,210
Everything we can see
in the night sky

443
00:22:06,211 --> 00:22:08,653
makes up just 4.8%

444
00:22:08,654 --> 00:22:11,364
of all the matter in the cosmos.

445
00:22:11,365 --> 00:22:13,639
The rest is the dark universe,

446
00:22:13,640 --> 00:22:15,945
including dark matter.

447
00:22:15,955 --> 00:22:20,237
We can't see it, feel it,
or detect it directly.

448
00:22:20,238 --> 00:22:22,878
But we know dark matter
is there.

449
00:22:22,879 --> 00:22:26,548
Its gravity is tugging
on everything around it.

450
00:22:26,549 --> 00:22:28,130
And we're beginning
to understand

451
00:22:28,131 --> 00:22:30,208
it plays a fundamental role

452
00:22:30,208 --> 00:22:32,680
in the formation
of the universe.

453
00:22:32,681 --> 00:22:35,055
Most of the stuff
that collects together

454
00:22:35,065 --> 00:22:36,944
gravitationally is dark matter.

455
00:22:36,945 --> 00:22:39,713
So perhaps black holes form

456
00:22:39,714 --> 00:22:42,613
somehow with the inclusion
of dark matter.

457
00:22:42,623 --> 00:22:44,432
One way of looking at it
is there's six times

458
00:22:44,433 --> 00:22:46,084
as much dark matter
as normal matter.

459
00:22:46,085 --> 00:22:48,527
So there's six times
as much food out there

460
00:22:48,528 --> 00:22:49,843
for the black holes to eat

461
00:22:49,844 --> 00:22:52,622
if they're able to tap
into this dark stuff.

462
00:22:52,623 --> 00:22:55,590
Maybe these supermassive
black holes are growing

463
00:22:55,591 --> 00:22:57,736
by eating dark matter.

464
00:22:57,737 --> 00:23:00,575
There are
some tantalizing clues.

465
00:23:00,576 --> 00:23:03,177
The largest supermassive
black holes

466
00:23:03,178 --> 00:23:06,184
don't live in the galaxies
with the most regular matter.

467
00:23:06,185 --> 00:23:09,982
They live in the galaxies
with the most dark matter.

468
00:23:09,983 --> 00:23:12,722
The one thing we know
about dark matter right now

469
00:23:12,723 --> 00:23:14,631
is that it has gravity.

470
00:23:14,632 --> 00:23:16,610
And a black hole runs
on gravity.

471
00:23:16,610 --> 00:23:18,232
It attracts anything with mass.

472
00:23:18,233 --> 00:23:20,081
So there's no reason to assume

473
00:23:20,082 --> 00:23:22,386
that black holes would
only eat regular matter.

474
00:23:22,387 --> 00:23:26,679
And now we know that there's far
more dark matter out there.

475
00:23:26,680 --> 00:23:31,694
Maybe dark matter
helps the black holes eat.

476
00:23:31,695 --> 00:23:34,168
Maybe in some ways,
dark matter is a feeder

477
00:23:34,178 --> 00:23:36,482
for these supermassive
black holes.

478
00:23:36,483 --> 00:23:39,351
Perhaps what really grows
a supermassive black hole

479
00:23:39,352 --> 00:23:42,427
is all of the regular matter
being directed into the center

480
00:23:42,428 --> 00:23:45,356
by the dark matter around it.

481
00:23:45,366 --> 00:23:48,263
Maybe the dark
matter's powerful gravity

482
00:23:48,264 --> 00:23:50,044
sucks in regular matter

483
00:23:50,054 --> 00:23:53,614
and funnels it
into the black hole.

484
00:23:53,615 --> 00:23:56,612
In a sense, the dark
matter is greasing the wheels.

485
00:23:56,613 --> 00:23:58,333
It's sort of tilting
the table up

486
00:23:58,334 --> 00:24:00,411
so that that food can
slide right in.

487
00:24:04,110 --> 00:24:07,047
But now scientists
think the dark matter

488
00:24:07,048 --> 00:24:10,936
may create gigantic
black holes directly

489
00:24:10,946 --> 00:24:15,228
by igniting dark stars.

490
00:24:15,229 --> 00:24:16,850
Some believe that dark matter

491
00:24:16,851 --> 00:24:19,550
sparked early universe
super stars.

492
00:24:19,551 --> 00:24:24,803
When they die, they leave behind
supermassive black holes.

493
00:24:24,804 --> 00:24:26,287
Dark stars sound like

494
00:24:26,288 --> 00:24:28,296
they come from
the fertile imagination

495
00:24:28,306 --> 00:24:30,343
of some Sci-Fi writer.

496
00:24:30,353 --> 00:24:33,380
But Dr. Katie Freese believes
they may explain

497
00:24:33,390 --> 00:24:38,701
how early supermassive
black holes grew so fast.

498
00:24:38,702 --> 00:24:40,115
Dark stars are amazing.

499
00:24:40,116 --> 00:24:42,489
So, when we first had this idea,

500
00:24:42,490 --> 00:24:43,776
we got excited really quickly,

501
00:24:43,786 --> 00:24:45,961
because this is
a new type of star

502
00:24:45,962 --> 00:24:49,156
that has never been seen before.

503
00:24:49,157 --> 00:24:51,896
Dark stars may have
been some of the first stars

504
00:24:51,897 --> 00:24:54,112
to form in the universe.

505
00:24:54,113 --> 00:24:55,625
They sparked into life

506
00:24:55,626 --> 00:24:59,455
when the universe was just
200 million years old.

507
00:24:59,464 --> 00:25:04,973
But how could dark stars form
really massive black holes?

508
00:25:04,974 --> 00:25:09,752
A newborn black hole can't weigh
more than its parent star.

509
00:25:09,762 --> 00:25:14,014
So in order to give birth to
a really massive black hole,

510
00:25:14,015 --> 00:25:18,465
the parent star has to be
supermassive, as well.

511
00:25:18,466 --> 00:25:21,008
These early objects
are really strange.

512
00:25:21,009 --> 00:25:23,154
They're very cool.

513
00:25:23,155 --> 00:25:25,568
And they're really, really big.

514
00:25:25,569 --> 00:25:28,961
The size of these things
is 10 times the distance

515
00:25:28,962 --> 00:25:31,543
between the Sun and the earth.

516
00:25:33,719 --> 00:25:36,222
But how is that possible?

517
00:25:36,232 --> 00:25:40,583
Regular stars have
an upper size limit.

518
00:25:40,584 --> 00:25:44,312
A star is a battle between
gravity pushing inwards

519
00:25:44,313 --> 00:25:46,559
and nuclear fusion pushing out.

520
00:25:49,962 --> 00:25:51,504
When the star grows too big,

521
00:25:51,505 --> 00:25:55,866
its gravity
becomes overwhelming.

522
00:25:55,867 --> 00:25:57,449
The delicate balance

523
00:25:57,450 --> 00:26:01,346
between gravity
and fusion is broken.

524
00:26:01,347 --> 00:26:06,193
Gravity wins out,
and the star collapses.

525
00:26:06,194 --> 00:26:09,032
But dark stars
may have a work-around

526
00:26:09,033 --> 00:26:13,256
that lets them
become supermassive.

527
00:26:13,257 --> 00:26:15,204
So, they are made
of ordinary matter.

528
00:26:15,205 --> 00:26:17,776
They're made
of hydrogen and helium.

529
00:26:17,777 --> 00:26:20,714
But they're powered
by dark matter.

530
00:26:20,715 --> 00:26:23,652
We don't know what
dark matter is made from.

531
00:26:23,653 --> 00:26:28,736
But we do have theories
on how it might power a star.

532
00:26:28,737 --> 00:26:31,308
One of the best ideas
we have for dark matter

533
00:26:31,309 --> 00:26:35,275
is that it's made of weakly
interacting massive particles,

534
00:26:35,276 --> 00:26:37,322
or wimps for short.

535
00:26:37,323 --> 00:26:39,696
So, these wimps are
their own antimatter.

536
00:26:39,697 --> 00:26:42,200
And that means, whenever
they encounter each other,

537
00:26:42,210 --> 00:26:45,997
they annihilate and turn
into something else.

538
00:26:45,998 --> 00:26:48,768
That means a lot of heat
is released, a lot of energy.

539
00:26:48,778 --> 00:26:52,072
And it's that energy
that could power stars.

540
00:26:54,980 --> 00:26:57,422
The energy
from the wimps' annihilations

541
00:26:57,423 --> 00:27:02,140
keeps the star from
collapsing like a normal star.

542
00:27:02,141 --> 00:27:04,416
So it's possible
that, in some stars,

543
00:27:04,417 --> 00:27:06,196
their internal reactions

544
00:27:06,197 --> 00:27:09,203
are actually being powered
by dark matter.

545
00:27:09,204 --> 00:27:12,072
If that's the case, then you
could imagine situations

546
00:27:12,073 --> 00:27:13,555
where, when that burns out,

547
00:27:13,556 --> 00:27:16,493
you produce very massive
black holes.

548
00:27:16,494 --> 00:27:18,116
So it could be that dark matter,

549
00:27:18,117 --> 00:27:19,500
the physics of dark matter,

550
00:27:19,501 --> 00:27:22,765
plays really important roles
in creating black holes

551
00:27:22,766 --> 00:27:25,278
and their prevalence
in the universe.

552
00:27:33,399 --> 00:27:35,635
The energy from the dark matter

553
00:27:35,645 --> 00:27:40,560
allows the dark stars
to grow huge.

554
00:27:40,561 --> 00:27:42,203
When they first form,
they're small.

555
00:27:42,213 --> 00:27:45,042
They're about the mass
of the Sun.

556
00:27:45,052 --> 00:27:47,059
But because they're so cool,

557
00:27:47,060 --> 00:27:48,345
they keep accumulating matter

558
00:27:48,346 --> 00:27:49,898
and growing, growing, growing.

559
00:27:49,899 --> 00:27:52,302
And some of them will get
to be a million times

560
00:27:52,312 --> 00:27:56,762
as massive as the Sun
and a billion times as bright.

561
00:27:56,763 --> 00:27:59,266
But these giants
don't live for long.

562
00:27:59,276 --> 00:28:01,649
Eventually,
the dark matter particles

563
00:28:01,650 --> 00:28:04,122
wipe each other out completely.

564
00:28:04,123 --> 00:28:05,606
And there is no more fuel

565
00:28:05,607 --> 00:28:08,148
to keep the massive amount
of ordinary matter

566
00:28:08,149 --> 00:28:10,660
from collapsing.

567
00:28:10,661 --> 00:28:12,075
And then that's it.

568
00:28:12,076 --> 00:28:14,686
There's nothing to sustain
this big, puffy object.

569
00:28:14,687 --> 00:28:19,533
If it's big enough, you collapse
directly to a black hole.

570
00:28:19,534 --> 00:28:24,093
A monster
supermassive black hole.

571
00:28:25,062 --> 00:28:27,366
It's really fun
to think about the possibility

572
00:28:27,367 --> 00:28:28,820
that the physics of dark matter

573
00:28:28,821 --> 00:28:31,194
is actually helping
to power stars.

574
00:28:31,195 --> 00:28:32,915
If so, it would bring, you know,

575
00:28:32,916 --> 00:28:35,320
a whole new window
into our understanding

576
00:28:35,330 --> 00:28:37,565
of stars and their evolution.

577
00:28:40,108 --> 00:28:44,627
At the moment, dark stars
are just theoretical.

578
00:28:44,628 --> 00:28:47,436
But when the powerful
James Webb telescope

579
00:28:47,437 --> 00:28:49,711
comes online in 2018,

580
00:28:49,712 --> 00:28:53,678
we may get our first glimpse.

581
00:28:53,679 --> 00:28:57,338
We're gonna do an observing
run and look f

582
00:28:57,339 --> 00:28:58,693
and so we're very excited.

583
00:28:58,694 --> 00:29:00,375
If you would find an entirely
new type of star,

584
00:29:00,376 --> 00:29:03,580
that would be huge.

585
00:29:03,581 --> 00:29:06,082
While Katie Freese
looks for dark stars,

586
00:29:06,083 --> 00:29:09,782
another team is investigating
another radical idea

587
00:29:09,783 --> 00:29:11,562
that offers new insight

588
00:29:11,563 --> 00:29:16,914
into how supermassive
black holes grow so huge.

589
00:29:16,915 --> 00:29:19,218
They detect the faint echoes

590
00:29:19,219 --> 00:29:23,284
of a violent event
from across the universe,

591
00:29:23,285 --> 00:29:26,716
the remnants of
an extraordinary collision,

592
00:29:26,717 --> 00:29:28,625
a supremely energetic event

593
00:29:28,626 --> 00:29:32,850
that reveals
black holes are cannibals.

594
00:29:42,058 --> 00:29:44,728
Our universe
is filled with enormous

595
00:29:44,729 --> 00:29:49,387
supermassive black holes
that defy explanation.

596
00:29:49,388 --> 00:29:51,296
Supermassive black holes
are one of the things

597
00:29:51,297 --> 00:29:53,344
in the universe that,
when you run the physics,

598
00:29:53,345 --> 00:29:55,589
when you run the math
of how did they evolve,

599
00:29:55,590 --> 00:29:57,637
they really shouldn't be there.

600
00:29:57,638 --> 00:30:00,604
It's still a profound mystery.

601
00:30:00,605 --> 00:30:02,584
The universe hasn't
been around long enough

602
00:30:02,594 --> 00:30:04,037
for regular black holes

603
00:30:04,038 --> 00:30:07,440
to eat enough matter
to get supermassive.

604
00:30:07,441 --> 00:30:09,449
So how did they get so big?

605
00:30:09,458 --> 00:30:10,842
The most logical answer

606
00:30:10,843 --> 00:30:13,978
is that large black holes
are born large,

607
00:30:13,979 --> 00:30:16,808
around 1 to 2 billion
solar masses.

608
00:30:16,818 --> 00:30:19,350
But that's still
over 10 times smaller

609
00:30:19,360 --> 00:30:23,781
than the largest supermassive
black holes out there.

610
00:30:23,782 --> 00:30:25,819
Given the time scales, it
doesn't seem to add up.

611
00:30:25,829 --> 00:30:27,470
We need some other way

612
00:30:27,471 --> 00:30:29,549
to make these
supermassive black holes.

613
00:30:29,558 --> 00:30:31,398
And the question is,
what is that?

614
00:30:33,683 --> 00:30:37,174
A clue came
from a large, isolated galaxy

615
00:30:37,175 --> 00:30:39,390
200 million light-years away

616
00:30:39,391 --> 00:30:41,666
in a quiet part of the universe.

617
00:30:43,585 --> 00:30:47,442
Nestling alone was
a supermassive black hole

618
00:30:47,443 --> 00:30:52,655
with a mass of 17 billion suns.

619
00:30:52,656 --> 00:30:54,277
Normally, such monsters

620
00:30:54,278 --> 00:30:57,076
are found in dense regions
of space

621
00:30:57,077 --> 00:31:01,537
with lots of galaxies
and lots of stars.

622
00:31:01,538 --> 00:31:03,941
This black holes doesn't match
its surroundings at all.

623
00:31:03,942 --> 00:31:06,186
It's kind of like driving
to the middle of a desert

624
00:31:06,187 --> 00:31:08,135
and coming across
the empire state building.

625
00:31:08,136 --> 00:31:10,845
Now, the empire state building
belongs in the middle of a city.

626
00:31:10,846 --> 00:31:12,390
And a black hole this big

627
00:31:12,399 --> 00:31:15,890
belongs in a rich cluster
of galaxies.

628
00:31:15,891 --> 00:31:18,630
This is the first time
astronomers have found

629
00:31:18,631 --> 00:31:20,213
such a giant object

630
00:31:20,214 --> 00:31:24,437
lurking in such a relatively
empty area of the universe.

631
00:31:24,438 --> 00:31:25,960
So you got to ask the question,

632
00:31:25,961 --> 00:31:28,859
if there's nothing else around,
how exactly do you grow

633
00:31:28,869 --> 00:31:31,401
a 17-billion-solar-mass
black hole?

634
00:31:34,577 --> 00:31:38,008
One possible answer
is the stuff of nightmares.

635
00:31:38,009 --> 00:31:40,056
Maybe the story
of this black hole

636
00:31:40,057 --> 00:31:42,360
is actually a little more
scary than we thought.

637
00:31:42,361 --> 00:31:43,547
Maybe it's all alone

638
00:31:43,548 --> 00:31:45,823
because it ate
all of its neighbors.

639
00:31:48,207 --> 00:31:51,441
Maybe it was eating
more than galaxies.

640
00:31:51,442 --> 00:31:54,805
Maybe it was eating
its own kind.

641
00:31:56,685 --> 00:31:58,861
The thing about black holes
is they're omnivores.

642
00:31:58,871 --> 00:32:00,284
They'll eat anything.

643
00:32:00,285 --> 00:32:02,658
Anything that gets close them,
they'll gobble up.

644
00:32:02,659 --> 00:32:04,638
One way black holes
can grow so large

645
00:32:04,647 --> 00:32:06,259
is by eating other black holes.

646
00:32:06,260 --> 00:32:09,059
So in a sense,
they may be cannibals.

647
00:32:09,069 --> 00:32:12,560
Cannibal black holes
were just theoretical.

648
00:32:12,561 --> 00:32:15,429
We'd never actually
seen them eat each other.

649
00:32:17,586 --> 00:32:21,344
Then scientists detected
the faint echoes

650
00:32:21,345 --> 00:32:24,974
of actual ripples
in space-time.

651
00:32:24,975 --> 00:32:26,527
When engineers turned on

652
00:32:26,528 --> 00:32:30,681
the laser interferometer
gravitational-wave observatory,

653
00:32:30,682 --> 00:32:32,699
or LIGO for short,

654
00:32:32,700 --> 00:32:34,579
they immediately picked up

655
00:32:34,580 --> 00:32:38,338
the faint signal
of gravitational waves.

656
00:32:38,339 --> 00:32:40,088
Gravitational waves are created

657
00:32:40,089 --> 00:32:42,899
by huge explosions in space.

658
00:32:46,094 --> 00:32:50,781
To make them, you need an almost
unimaginably energetic event,

659
00:32:50,782 --> 00:32:53,493
something really, really big...

660
00:32:55,699 --> 00:32:59,863
...something like
merging black holes.

661
00:33:01,772 --> 00:33:04,047
A black hole merger
is the most violent,

662
00:33:04,057 --> 00:33:05,333
the most energetic thing

663
00:33:05,343 --> 00:33:07,578
that happens
in the universe, period.

664
00:33:10,427 --> 00:33:14,344
Picture the scene,
1.3 billion years ago.

665
00:33:14,354 --> 00:33:18,409
Two black holes circle each
other in a dance of death.

666
00:33:18,410 --> 00:33:22,168
The larger black hole
pulls the smaller one inwards

667
00:33:22,169 --> 00:33:25,600
until they're locked together
in a spiral.

668
00:33:25,601 --> 00:33:28,043
Very, very slowly,
that orbit is decaying.

669
00:33:28,044 --> 00:33:30,122
They're getting closer
and closer and closer.

670
00:33:30,132 --> 00:33:33,554
And then they will merge
into one giant black hole,

671
00:33:33,564 --> 00:33:37,351
truly one of the most dramatic
events in the universe.

672
00:33:37,352 --> 00:33:39,399
Finally, they collide

673
00:33:39,400 --> 00:33:43,129
in one of the largest bangs
since the big bang.

674
00:33:46,334 --> 00:33:48,242
I would have loved
to have been able

675
00:33:48,243 --> 00:33:50,024
to safely view the collision

676
00:33:50,034 --> 00:33:52,140
of these two
black holes up close.

677
00:33:52,141 --> 00:33:53,426
Imagine these two black holes

678
00:33:53,427 --> 00:33:55,305
as they spiral
in toward each other,

679
00:33:55,306 --> 00:33:57,482
going faster and faster
and faster and faster.

680
00:33:57,492 --> 00:34:00,024
And then, suddenly, where
there appears to be nothing

681
00:34:00,034 --> 00:34:02,506
or just distortions in space
in front of you,

682
00:34:02,507 --> 00:34:05,770
suddenly, there is this
enormous burst of energy.

683
00:34:05,771 --> 00:34:08,906
And everything
just rains around you.

684
00:34:08,907 --> 00:34:12,269
By measuring the frequency

685
00:34:12,270 --> 00:34:16,494
we can calculate the size
of the objects causing them.

686
00:34:16,504 --> 00:34:18,244
When those two black holes,

687
00:34:18,245 --> 00:34:20,786
weighing 29 solar masses

688
00:34:20,787 --> 00:34:24,515
and 36 solar masses, collided,

689
00:34:24,516 --> 00:34:28,582
they created a black hole
around twice the size.

690
00:34:30,590 --> 00:34:33,101
In some ways,
it's very elegant and simple.

691
00:34:33,102 --> 00:34:35,277
You take two black holes.
You spiral them in together.

692
00:34:35,278 --> 00:34:38,246
And you end up
with one big black hole.

693
00:34:40,363 --> 00:34:43,794
The event showed that black
holes can double their mass

694
00:34:43,795 --> 00:34:47,454
through cannibalism... Almost.

695
00:34:47,455 --> 00:34:52,113
The final black hole was less
than the sum of its parts.

696
00:34:52,114 --> 00:34:55,377
There were 3 solar masses
missing.

697
00:34:55,378 --> 00:34:57,553
That may not sound like a lot.

698
00:34:57,554 --> 00:35:00,126
So let's put it in context.

699
00:35:00,136 --> 00:35:02,311
Our sun is burning

700
00:35:02,312 --> 00:35:05,210
about 100 billion
hydrogen bombs every second.

701
00:35:05,211 --> 00:35:07,189
And over its
10-billion-year lifetime,

702
00:35:07,199 --> 00:35:09,671
it will convert less
than maybe 1% of the mass

703
00:35:09,672 --> 00:35:10,858
of the Sun to energy.

704
00:35:10,859 --> 00:35:13,034
In 2/10 of a second,

705
00:35:13,035 --> 00:35:15,805
3 times the mass
of the Sun in matter

706
00:35:15,815 --> 00:35:18,446
got converted to energy
in that collision.

707
00:35:20,365 --> 00:35:24,261
It was 36 septillion yottawatts.

708
00:35:24,262 --> 00:35:26,794
What does that mean?
A lot of freaking energy.

709
00:35:26,804 --> 00:35:29,998
That's more energy
in that 2/10 of a second

710
00:35:29,999 --> 00:35:32,115
than is emitted by all the stars

711
00:35:32,116 --> 00:35:34,164
in the visible universe
in the same time.

712
00:35:36,706 --> 00:35:40,069
In its first run,
LIGO detected two collisions.

713
00:35:42,186 --> 00:35:44,292
This suggests
that cannibal black holes

714
00:35:44,293 --> 00:35:45,973
are relatively common

715
00:35:45,974 --> 00:35:50,098
and that each feast
builds a larger black hole.

716
00:35:50,099 --> 00:35:52,413
But so far,
the largest black hole

717
00:35:52,414 --> 00:35:54,193
these mergers have produced

718
00:35:54,194 --> 00:35:56,637
is 62 solar masses,

719
00:35:56,638 --> 00:36:01,781
not close to the largest
supermassives we've found.

720
00:36:01,791 --> 00:36:03,966
It's hard to imagine,
in 13.8 billion years,

721
00:36:03,967 --> 00:36:06,835
that there'd be enough
collisions of 30-solar-mass

722
00:36:06,836 --> 00:36:11,128
black holes to build up to form a
billion-solar-mass black hole.

723
00:36:11,129 --> 00:36:14,066
That's 100 million collisions.

724
00:36:14,067 --> 00:36:17,696
So maybe small
black holes eating each other

725
00:36:17,697 --> 00:36:19,279
isn't the solution.

726
00:36:19,280 --> 00:36:22,475
Maybe supermassive black holes

727
00:36:22,485 --> 00:36:25,382
are eating each other.

728
00:36:25,383 --> 00:36:28,191
If so, could
the supermassive black hole

729
00:36:28,192 --> 00:36:32,416
at the heart of our own galaxy
be on the menu?

730
00:36:46,937 --> 00:36:49,379
We've found
supermassive black holes

731
00:36:49,380 --> 00:36:53,169
so large, they defy explanation.

732
00:36:53,179 --> 00:36:54,562
They're too big to have grown

733
00:36:54,563 --> 00:36:58,786
by simply eating
the matter around them.

734
00:36:58,787 --> 00:37:02,279
They can't form the same way
that regular black holes do.

735
00:37:02,289 --> 00:37:04,920
There must be something else
that happens that lets them grow

736
00:37:04,930 --> 00:37:07,728
to such enormous mass.

737
00:37:07,729 --> 00:37:10,567
Too large to have
grown from dark stars

738
00:37:10,568 --> 00:37:14,366
and too big to have grown
from regular black holes

739
00:37:14,367 --> 00:37:16,670
simply eating each other.

740
00:37:16,671 --> 00:37:19,045
Merging black holes
almost certainly play a role

741
00:37:19,055 --> 00:37:21,884
in our understanding
of supermassive black holes.

742
00:37:21,894 --> 00:37:25,088
We think that supermassive black
holes themselves also merge

743
00:37:25,089 --> 00:37:28,125
and have merged regularly over
the course of the universe.

744
00:37:28,126 --> 00:37:30,074
Now, whether this
merging activity itself

745
00:37:30,075 --> 00:37:32,151
is enough to make them that big,

746
00:37:32,152 --> 00:37:34,526
the jury is still out on that.

747
00:37:34,536 --> 00:37:37,631
Now a newly discovered
type of galaxy

748
00:37:37,632 --> 00:37:39,975
may provide an answer.

749
00:37:39,976 --> 00:37:45,782
It's called w2246-0526.

750
00:37:45,783 --> 00:37:47,305
And we can't see it.

751
00:37:47,306 --> 00:37:50,836
But we can detect
the heat it gives off.

752
00:37:50,837 --> 00:37:52,943
This galaxy is an example

753
00:37:52,944 --> 00:37:57,068
of a rare class
of objects called hot dogs.

754
00:37:57,069 --> 00:37:59,709
One of the funnier terms f

755
00:37:59,710 --> 00:38:01,293
is a hot dog galaxy.

756
00:38:01,303 --> 00:38:03,577
And no, this is not
some delicious sausage snack.

757
00:38:03,578 --> 00:38:07,801
In fact, it means "hot,
dust-obscured galaxy."

758
00:38:07,802 --> 00:38:10,343
It's called obscured
because it's shrouded

759
00:38:10,344 --> 00:38:14,528
in so much dust and gas,
the only light that escapes

760
00:38:14,538 --> 00:38:19,087
is infrared in the form of heat.

761
00:38:19,088 --> 00:38:20,937
All this heat must be
coming from somewhere.

762
00:38:20,938 --> 00:38:23,707
So in the core,
there is a cauldron,

763
00:38:23,708 --> 00:38:25,617
a seething
supermassive black hole,

764
00:38:25,627 --> 00:38:27,466
the likes of which
we can't even imagine.

765
00:38:30,642 --> 00:38:32,748
Of all the supermassive
black holes we know of,

766
00:38:32,749 --> 00:38:35,191
the ones that are obscured
in these hot dog galaxies

767
00:38:35,192 --> 00:38:37,238
may be the ones
that are the most ravenous,

768
00:38:37,239 --> 00:38:38,821
consuming many millions of times

769
00:38:38,822 --> 00:38:41,790
the mass of the Sun.

770
00:38:41,799 --> 00:38:44,172
Scientists theorize
that hot dogs

771
00:38:44,173 --> 00:38:46,378
could be the offspring

772
00:38:46,379 --> 00:38:49,910
of cannibal giant black holes.

773
00:38:49,911 --> 00:38:51,988
When the monstrous
black holes merge,

774
00:38:51,998 --> 00:38:54,964
they drag gas and dust
with them.

775
00:38:54,965 --> 00:38:57,507
This brings more food
to the table,

776
00:38:57,507 --> 00:39:01,463
allowing the new black hole
to gorge itself.

777
00:39:01,464 --> 00:39:04,135
When you have these
two galaxies merging,

778
00:39:04,145 --> 00:39:07,012
they have all-new food.

779
00:39:07,013 --> 00:39:08,101
It's a brand-new dinner plate,

780
00:39:08,102 --> 00:39:11,998
a brand-new buffet
of food to eat.

781
00:39:11,999 --> 00:39:15,193
The combination
of cannibalism and fresh food

782
00:39:15,194 --> 00:39:18,260
allows the black holes
to grow super large.

783
00:39:21,416 --> 00:39:24,422
Perhaps this is how
the supermassive black hole

784
00:39:24,423 --> 00:39:26,133
at the center of our galaxy

785
00:39:26,134 --> 00:39:28,774
grew when it was young.

786
00:39:28,775 --> 00:39:30,358
But what's the future

787
00:39:30,368 --> 00:39:35,144
of our supermassive
Sagittarius "a" -star?

788
00:39:35,145 --> 00:39:37,192
As far as
supermassive black holes go,

789
00:39:37,193 --> 00:39:38,547
Sagittarius "a" -star

790
00:39:38,548 --> 00:39:40,457
is actually still kind of
in the minor leagues.

791
00:39:40,467 --> 00:39:42,801
It's small.
But it's not done yet.

792
00:39:42,802 --> 00:39:46,767
It's still eating.
It's still growing.

793
00:39:46,768 --> 00:39:49,013
And in around 4 billion years,

794
00:39:49,014 --> 00:39:53,860
it's going to become
25 times larger,

795
00:39:53,861 --> 00:39:57,758
because it's going to be
eaten by its neighbor.

796
00:40:02,575 --> 00:40:06,175
The giant Andromeda galaxy
is heading our way.

797
00:40:06,176 --> 00:40:09,607
And it's going to engulf
our milky way.

798
00:40:09,608 --> 00:40:11,052
When galaxies merge,

799
00:40:11,062 --> 00:40:15,117
their central supermassive
black holes merge.

800
00:40:15,118 --> 00:40:18,154
Andromeda's huge
supermassive black hole

801
00:40:18,155 --> 00:40:21,646
will drag Sagittarius "a" -star
into orbit...

802
00:40:23,832 --> 00:40:27,660
...gradually drawing it closer
and closer

803
00:40:27,661 --> 00:40:29,273
until it devours it.

804
00:40:32,250 --> 00:40:34,554
The new supermassive
black hole will weigh

805
00:40:34,555 --> 00:40:38,116
around 100 million solar masses.

806
00:40:38,126 --> 00:40:40,598
But the disruption
to the new galaxy

807
00:40:40,599 --> 00:40:43,893
will provide the new
supermassive black hole

808
00:40:43,903 --> 00:40:45,247
with plenty to eat

809
00:40:45,248 --> 00:40:48,750
and the opportunity to grow
a whole lot bigger.

810
00:40:51,391 --> 00:40:53,399
At present,
there are many theories

811
00:40:53,409 --> 00:40:57,592
of how supermassive
black holes get so big.

812
00:40:57,593 --> 00:41:01,253
Most likely, it's a
combination of them all.

813
00:41:01,263 --> 00:41:05,347
But however it happens,
we can be pretty sure

814
00:41:05,348 --> 00:41:09,907
it's one of the most spectacular
things in the universe.

815
00:41:11,000 --> 00:41:13,076
The jury's still out on exactly

816
00:41:13,077 --> 00:41:16,213
how supermassive black holes
become so massive.

817
00:41:19,477 --> 00:41:21,159
Making all
the black holes we see

818
00:41:21,169 --> 00:41:23,998
probably requires
a pretty diverse cookbook.

819
00:41:24,008 --> 00:41:26,282
So any physicist who's looking
for a really simple,

820
00:41:26,283 --> 00:41:28,488
single answer
for how they get made,

821
00:41:28,489 --> 00:41:31,821
they're probably
gonna be disappointed.

822
00:41:31,822 --> 00:41:34,661
It's probably a pretty complex
thing that's going on.

823
00:41:38,390 --> 00:41:41,594
It could be through eating.

824
00:41:41,595 --> 00:41:42,910
It could be through
eating and merging.

825
00:41:42,911 --> 00:41:45,353
And usually, the answer
is somewhere in the middle.

826
00:41:45,354 --> 00:41:47,697
So they will merge
with other black holes.

827
00:41:47,698 --> 00:41:50,963
And they'll also have
a few snacks between mergers.

828
00:41:51,013 --> 00:41:55,563
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