How the Universe Works (2010–…): Season 5, Episode 2 - Black Holes: The Secret Origin - full transcript
The question in every galaxy and super anomaly students and viewers minds are how do black holes grow so massive. For every possible solution, there exists a different cause. The study continues.
Two black holes
circle each other
in a dance of death.
They spiral inwards,
their immense gravities
pulling them ever closer.
When they finally collide,
it's one of the most
powerful events
since the big bang.
This explosive mystery
sends ripples
across the world of science.
But can it also answer
one of the most pressing
questions in cosmology?
How do supermassive
black holes grow so large?
Captions paid for by
Discovery communications
In the known universe,
there are roughly
2,000 billion galaxies.
Each one has a different
shape and size.
But they may all have
one feature in common...
a supermassive black hole
buried at their center.
As its name says,
it is supermassive.
And here, we're talking
about objects
that are millions
or billions of times
the mass of the Sun.
Supermassive black holes
are so big
that we need a special scale
for measuring them.
A solar mass
is the mass of the Sun.
So when we study the universe,
we have to use the tools
that we have in hand.
And what's the most massive
thing that we have around us?
It's the Sun.
And so we refer to things
in multiples
of the mass of the Sun
because it just makes it easier
to wrap our heads around.
However, if you have something
that's 17 billion times
the mass of the Sun,
that's pretty difficult
to wrap your head around anyway.
But we know that those
kinds of black holes
live in the centers of galaxies.
The supermassive black hole
the milky way, is called
Sagittarius "a" -star.
It weighs in
at 4 million solar masses.
But compared to the other
supermassive black holes
out there, it's puny.
This is probably
one of the only contexts
where you would think that
our supermassive black hole
isn't very supermassive.
The supermassive black hole
in our neighboring galaxy,
Andromeda,
is 25 times larger
than Sagittarius "A" -star,
coming in at
100 million solar masses.
But compared
to the largest monsters
out in the universe,
it's a runt.
O.J. 287's primary
supermassive black hole
weighs in
at 18 billion solar masses.
And the black hole
in the core of galaxy NGC 4889
in the coma cluster
weighs 21 billion solar stars.
That's over 5,000 times larger
than Sagittarius "a" -star.
These are incredible things
that are more massive
than some galaxies.
Now astronomers may have ma
a giant, new
supermassive black hole
that's a mind-blowing
30 billion times
the mass of the Sun.
It's a huge puzzle.
And we have simply no idea
how it got so big.
It's a huge mystery how black
we started finding
black holes with millions
and billions of times
the Sun's mass.
No one expected that.
And we have no idea
how they got to be so big.
It's not entirely
clear at this point
how supermassive black holes
can get to be the masses
that they are today.
Regular-sized black holes form
when large stars over 20 times
the mass of our sun
crash and burn.
When a large star
runs out of fuel,
the core stops generating
enough outward force
to counteract the power
of gravity crushing inwards.
As the star collapses,
the outer part explodes
in a supernova.
The inner core shrinks
from a sphere
millions of miles wide
to one just 10 miles across.
It's like shrinking
the earth down
to the size of a golf ball.
This rapid collapse
creates a black hole.
So we now have seen black holes
that are solar-mass black
holes
and black holes that are million
or billion-solar-mass
black holes.
And the question is, how do you
get from one to the other?
Do the giants somehow grow
from a solar-mass black hole?
One of the big puzzles today is,
how do you make one of these
supermassive black holes?
One idea is,
you get there by starting
with a solar-mass black hole,
having it grow through a stage
of being an intermediate-mass
black hole
and then eventually
getting to be
a supermassive black hole.
Theoretically,
intermediate-mass black holes
should be between 100
and 100,000 solar masses.
But we've never seen one.
Part of the mystery
of supermassive black holes
is that black holes seem
to occur in two flavors.
You have ones that are
only a couple times
the mass of the Sun.
And you have ones
that are millions
or billions of times
the mass of the Sun.
So we have small
and extra large.
If we think
of the stellar-mass black hole
as sort of the baby black holes,
and the supermassive black holes
as the grown-up black holes,
we're missing
the teenage black holes.
Where are these black holes
that have masses
that are between stellar mass
and supermassive?
They're sort of like
a holy grail
for black hole hunters.
Where are these things?
Where can we find them?
And how do you make them?
Then astronomers caught a break.
They picked up a burst of energy
coming from the NGC 1399 galaxy.
It was the death throes
of a star being eaten
by a black hole.
When they measured its size,
they discovered it was
an elusive intermediate-mass
black hole.
The missing link had been found.
But when scientists did the math
to see if such an
intermediate-mass black hole
could grow into
a supermassive black hole,
they hit a snag.
There hasn't been enough time
since the birth of the universe
for an intermediate-mass
black hole
to eat enough stars
to grow into
a supermassive black hole.
It doesn't seem like
there's enough time
for black holes to get
as big as we see them.
But supermassives
are everywhere we look.
How did they get there?
And how did they grow so huge?
In our universe, we've
detected small black holes.
And we've seen monsters,
supermassive black holes
billions of times
the mass of our sun.
But we'd found
almost none in between.
So how do you get from a small
black hole to a giant one?
One of the most important
outstanding questions
in cosmology is,
how did supermassive black holes
get as big as they are?
And when did that happen?
Black holes are normally S
an all-you-can-eat buffet.
One of the best ideas
for how black holes grow
is that black holes do
what we expect
black holes to do,
and that is eat stuff.
For a black hole,
it's almost as if the universe
is its restaurant.
And on its menu,
you'll find stars, planets,
and clouds of gas and dust.
So is binge-eating the answer
to growing
a supermassive black hole?
Theoretically, black holes
should keep on growing forever
as they consume
more and more food.
But recent discoveries suggest
that the universe
puts them on a diet,
controlling how much they eat.
Black holes are hungry.
They like to eat.
But sometimes,
they eat too much,
and they burp it up.
February 2015.
Astronomers report
something unusual
in the galaxy NGC 2276.
It looked like something
had taken a bite
out of one of its spiral arms.
Sitting alone in the void
was an intermediate-mass
black hole,
about 50,000 times
the mass of the Sun.
One theory
was that the black hole
had eaten everything around it,
creating the dead zone.
But the detection
of a burst of energy
from the black hole suggests
it may have tried
to eat too much
and, in the process,
destroyed its food source,
burping so hard,
its food was blasted away.
Turns out that black holes
are actually very messy
a lot of matter gets thrown
off as it tries to absorb it.
So things move in, gets hot.
But then a lot of it gets
thrown all the way back out.
Black holes
are not vacuums in space.
They do not just eat
everything around them.
And so they are messy.
Some things get in.
And they take that on.
And it grows their mass.
And some things are just
flung out as they're eating.
The enormous gravity of black
holes sucks gas, dust,
and even stars towards them.
Everybody's been to
an all-you-can-eat buffet.
But let's be honest.
There really is a limit
to how much you can eat.
Black holes
are gluttons. They're greedy.
They don't really know
when they've eaten too much.
They just keep on cramming in
more and more food.
It doesn't just fall in.
It has to go down the drain,
more or less.
And so it forms this disk
around the hole.
And as it does that,
there's a lot of turbulence
and magnetic fields
and a witch's brew of forces
going on there
that get it really hot.
As the gas
and dust swirls around,
it heats up,
pushing temperatures to
millions of degrees Fahrenheit.
This swirl, called
the accretion disk,
also generates powerful
magnetic fields.
These fields are dragged
by the SPiN of the black hole
and become focused
above the poles.
As energy builds up,
the magnetic fields
become so compressed
they blast out
super-energized particles.
These beams can actually
be incredibly violent.
Matter is flung out
at a large fraction
of the speed of light.
It's a tremendous wind
that blows very hard away
from the black hole.
The jet hits the gas clouds
surrounding the black hole,
blowing the buffet away.
If they eat too much,
they can basically
blow everything
that's in their vicinity away.
They lose their food supply.
And then they're gonna starve.
They can kind of shoot
themselves in the foot.
With no food available,
the black hole stops growing.
Astronomers think
that's what happened
to the intermediate-mass
black hole
they discovered
in the dead zone.
These burps may
regulate star formation
and stop the black hole
from getting obese.
But over time,
the black hole
will start eating again
as gas falls back towards it.
But can an intermediate-mass
black hole eat enough
to become
a supermassive black hole
weighing billions
of solar masses?
Could that black hole
become so obese by eating?
That's a really
interesting question.
You'd have to eat
a heck of a lot
to get that fat.
When you think about it, if
you imagine an average galaxy
has 100 billion stars,
the black hole
would have to eat one
in every five stars
in the galaxy.
The universe is old.
But is it really old enough
that black holes have had time
to consume billions of stars?
That seems kind of unlikely.
It doesn't seem to add up.
We need some other way
to make these
supermassive black holes.
And the question is,
what is that?
Maybe we've been making
this all too complicated.
Maybe to get a big black hole is
to start big in the first place.
So how can black
holes start big?
To answer that question,
scientists had to journey back
to the very start
of the universe,
to a mysterious time
called the dark ages.
As we look out
into the universe,
we're seeing farther
and farther back in time.
We have now looked back
over 12 billion years
to the time when the cosmos
was still an infant.
And what we found
was a huge surprise.
We had made the assumption
that as you look farther
out into the universe,
the black holes
would be smaller.
They haven't had
much time to grow.
But now we've found
a 12-billion-solar-mass
black hole that's actually less
than a billion years
into the universe.
How did this thing
form so early?
How did it grow so fast?
This is like walking
into a delivery room
and finding a 100-pound baby.
I mean, how does that
even happen?
It doesn't make any sense.
Physics tells us no black hole
could swallow enough stuff
to get that big that quickly.
There really wasn't enough
time between the big bang
and when we're
studying these things
for them to grow
to such large sizes
just by eating
matter around them.
So if there's not enough time
maybe they're born supermassive.
To understand how, we have
to travel back even farther,
to not long after
the birth of the universe.
The early universe
was definitely
a much more compact
and richer place for material.
It was smaller,
and it was denser.
Things were much closer.
It was hotter.
It was just a much
more intense place to be.
Clouds of hydrogen and
helium gas clumped together.
As the clouds grew,
so did their gravity,
sucking in more and more gas.
Eventually, the ball of gas
became so dense, it collapsed,
triggering nuclear fusion.
A star was born.
These massive first stars
are called population III stars.
Because there was
so much food around,
these stars were huge,
many times bigger than
any stars that exist today.
We think a lot of these
population III stars
probably were
incredibly massive,
incredibly short-lived,
and just blew up right away.
They would've left massive
black holes behind.
With so much food available,
these young, ravenous
black holes, called quasars,
started binge-eating
and became incredibly bright.
Billions of years later, we
can still see their gluttony.
The most luminous,
bright objects in the universe
are things called quasars.
And it may seem kind of ironic.
But what these really are
are supermassive black holes.
There's so much stuff
trying to cram itself down
the black hole that everything
gets very hot, very energetic.
And you can see them
clear across the universe.
But when we measured
the size of the young quasars,
we discovered they were already
billions of solar masses.
There's not enough time,
a billion years after
the universe was created,
for them to get to
a billion solar masses in...
it's just too short a time.
So the question becomes,
that are this big
in that small amount of time?
We need some other way
of growing these
supermassive black holes.
There needs to be
some other mechanism
that allows them
to get that massive so early.
But what is that?
A clue can be found
in the very early universe.
The early universe is still
so much of a mystery to us.
We know that conditions
were very different.
It was denser.
There was a lot more material.
This period
is called the dark ages.
During the dark age, we know
that there was
basically nothing happening.
Matter existed.
We think that there
was hydrogen and helium gas
but really not much else.
There were a few stars around,
but nothing large enough
to form giant black holes.
But there were
huge clouds of gas.
And because the universe
was much smaller and denser,
the clouds were much thicker.
The idea is that
from these basic ingredients,
gravity and gas,
the cosmos built
massive black holes.
Somehow, the universe
has created a shortcut
to the black hole.
We've typically
thought of it as,
cloud of gas
collapses into a star,
star evolves, star dies,
leaves behind a black hole.
Perhaps the universe
has found a way
to skip the star phase
and go directly
to the black hole.
Clouds of gas may have
built massive black holes
in a process
called direct collapse.
As they collapsed,
they never even formed a star.
They just collapsed straight
into a giant black hole.
Through this direct
collapse theory,
you can form really
big black holes.
Imagine what it's like seeing
one of these giant clouds
of gas collapsing down
into a black hole.
You might think
you start with, okay,
cloud of gas slowly collapsing,
and, boop, it's a black hole.
That wouldn't be the case.
It would be more like
giant cloud of gas
starts collapsing,
then... aah! Black hole.
It's believed
that direct collapse
could have created black holes
up to a million times
the mass of the Sun,
much bigger
than from the collapse
of a single star.
These early black holes
are sort of like the galaxies
that never were.
They were gonna make galaxies.
But instead, they collapsed
into very massive black holes.
For direct collapse
to form a black hole,
the conditions need
to be precise.
The clouds must be
very symmetrical,
forming a smooth ball.
If you have a ball of gas
that isn't quite a ball,
that's not quite homogeneous,
as it collapses, it'll fragment.
And it'll fragment into objects
that won't form black holes.
So you want it to be hot enough
that it stays
one big, giant thing.
But it does need to cool
a little bit, right,
so that you get it
to collapse in on itself.
You have to get
uniform collapse over time
of a very large amount
of hydrogen gas, presumably,
which is the original matter
in the universe,
collapsing spherically
symmetrically,
without fragmenting,
over a period of less
than 500 million years.
Direct collapse
may have created black holes
a million times
the mass of the Sun.
But it can't completely explain
the 12 billion solar-mass
supermassive black holes
we see in the early universe.
Maybe gigantic supermassive
black holes were created
by strange, unseen forces.
Maybe they were created
by the mysterious dark universe.
Astronomers looking
deep into the early universe
have discovered gigantic
supermassive black holes.
This is a pretty deep mystery.
There are these
supermassive black holes
that exist
in the very early universe.
And by all accounts,
they should not exist.
According to
the normal laws of physics,
it shouldn't have been possible
for them to grow so big
so quickly.
For astrophysicists,
understanding how black holes
have grown to be so large is
one of our biggest mysteries.
We need some other way
of growing these
supermassive black holes.
There needs to be
some other mechanism
that allows them
to get that massive so early.
But what is that?
Everything we can see
in the night sky
makes up just 4.8%
of all the matter in the cosmos.
The rest is the dark universe,
including dark matter.
We can't see it, feel it,
or detect it directly.
But we know dark matter
is there.
Its gravity is tugging
on everything around it.
And we're beginning
to understand
it plays a fundamental role
in the formation
of the universe.
Most of the stuff
that collects together
gravitationally is dark matter.
So perhaps black holes form
somehow with the inclusion
of dark matter.
One way of looking at it
is there's six times
as much dark matter
as normal matter.
So there's six times
as much food out there
for the black holes to eat
if they're able to tap
into this dark stuff.
Maybe these supermassive
black holes are growing
by eating dark matter.
There are
some tantalizing clues.
The largest supermassive
black holes
don't live in the galaxies
with the most regular matter.
They live in the galaxies
with the most dark matter.
The one thing we know
about dark matter right now
is that it has gravity.
And a black hole runs
on gravity.
It attracts anything with mass.
So there's no reason to assume
that black holes would
only eat regular matter.
And now we know that there's far
more dark matter out there.
Maybe dark matter
helps the black holes eat.
Maybe in some ways,
dark matter is a feeder
for these supermassive
black holes.
Perhaps what really grows
a supermassive black hole
is all of the regular matter
being directed into the center
by the dark matter around it.
Maybe the dark
matter's powerful gravity
sucks in regular matter
and funnels it
into the black hole.
In a sense, the dark
matter is greasing the wheels.
It's sort of tilting
the table up
so that that food can
slide right in.
But now scientists
think the dark matter
may create gigantic
black holes directly
by igniting dark stars.
Some believe that dark matter
sparked early universe
super stars.
When they die, they leave behind
supermassive black holes.
Dark stars sound like
they come from
the fertile imagination
of some Sci-Fi writer.
But Dr. Katie Freese believes
they may explain
how early supermassive
black holes grew so fast.
Dark stars are amazing.
So, when we first had this idea,
we got excited really quickly,
because this is
a new type of star
that has never been seen before.
Dark stars may have
been some of the first stars
to form in the universe.
They sparked into life
when the universe was just
200 million years old.
But how could dark stars form
really massive black holes?
A newborn black hole can't weigh
more than its parent star.
So in order to give birth to
a really massive black hole,
the parent star has to be
supermassive, as well.
These early objects
are really strange.
They're very cool.
And they're really, really big.
The size of these things
is 10 times the distance
between the Sun and the earth.
But how is that possible?
Regular stars have
an upper size limit.
A star is a battle between
gravity pushing inwards
and nuclear fusion pushing out.
When the star grows too big,
its gravity
becomes overwhelming.
The delicate balance
between gravity
and fusion is broken.
Gravity wins out,
and the star collapses.
But dark stars
may have a work-around
that lets them
become supermassive.
So, they are made
of ordinary matter.
They're made
of hydrogen and helium.
But they're powered
by dark matter.
We don't know what
dark matter is made from.
But we do have theories
on how it might power a star.
One of the best ideas
we have for dark matter
is that it's made of weakly
interacting massive particles,
or wimps for short.
So, these wimps are
their own antimatter.
And that means, whenever
they encounter each other,
they annihilate and turn
into something else.
That means a lot of heat
is released, a lot of energy.
And it's that energy
that could power stars.
The energy
from the wimps' annihilations
keeps the star from
collapsing like a normal star.
So it's possible
that, in some stars,
their internal reactions
are actually being powered
by dark matter.
If that's the case, then you
could imagine situations
where, when that burns out,
you produce very massive
black holes.
So it could be that dark matter,
the physics of dark matter,
plays really important roles
in creating black holes
and their prevalence
in the universe.
The energy from the dark matter
allows the dark stars
to grow huge.
When they first form,
they're small.
They're about the mass
of the Sun.
But because they're so cool,
they keep accumulating matter
and growing, growing, growing.
And some of them will get
to be a million times
as massive as the Sun
and a billion times as bright.
But these giants
don't live for long.
Eventually,
the dark matter particles
wipe each other out completely.
And there is no more fuel
to keep the massive amount
of ordinary matter
from collapsing.
And then that's it.
There's nothing to sustain
this big, puffy object.
If it's big enough, you collapse
directly to a black hole.
A monster
supermassive black hole.
It's really fun
to think about the possibility
that the physics of dark matter
is actually helping
to power stars.
If so, it would bring, you know,
a whole new window
into our understanding
of stars and their evolution.
At the moment, dark stars
are just theoretical.
But when the powerful
James Webb telescope
comes online in 2018,
we may get our first glimpse.
We're gonna do an observing
run and look f
and so we're very excited.
If you would find an entirely
new type of star,
that would be huge.
While Katie Freese
looks for dark stars,
another team is investigating
another radical idea
that offers new insight
into how supermassive
black holes grow so huge.
They detect the faint echoes
of a violent event
from across the universe,
the remnants of
an extraordinary collision,
a supremely energetic event
that reveals
black holes are cannibals.
Our universe
is filled with enormous
supermassive black holes
that defy explanation.
Supermassive black holes
are one of the things
in the universe that,
when you run the physics,
when you run the math
of how did they evolve,
they really shouldn't be there.
It's still a profound mystery.
The universe hasn't
been around long enough
for regular black holes
to eat enough matter
to get supermassive.
So how did they get so big?
The most logical answer
is that large black holes
are born large,
around 1 to 2 billion
solar masses.
But that's still
over 10 times smaller
than the largest supermassive
black holes out there.
Given the time scales, it
doesn't seem to add up.
We need some other way
to make these
supermassive black holes.
And the question is,
what is that?
A clue came
from a large, isolated galaxy
200 million light-years away
in a quiet part of the universe.
Nestling alone was
a supermassive black hole
with a mass of 17 billion suns.
Normally, such monsters
are found in dense regions
of space
with lots of galaxies
and lots of stars.
This black holes doesn't match
its surroundings at all.
It's kind of like driving
to the middle of a desert
and coming across
the empire state building.
Now, the empire state building
belongs in the middle of a city.
And a black hole this big
belongs in a rich cluster
of galaxies.
This is the first time
astronomers have found
such a giant object
lurking in such a relatively
empty area of the universe.
So you got to ask the question,
if there's nothing else around,
how exactly do you grow
a 17-billion-solar-mass
black hole?
One possible answer
is the stuff of nightmares.
Maybe the story
of this black hole
is actually a little more
scary than we thought.
Maybe it's all alone
because it ate
all of its neighbors.
Maybe it was eating
more than galaxies.
Maybe it was eating
its own kind.
The thing about black holes
is they're omnivores.
They'll eat anything.
Anything that gets close them,
they'll gobble up.
One way black holes
can grow so large
is by eating other black holes.
So in a sense,
they may be cannibals.
Cannibal black holes
were just theoretical.
We'd never actually
seen them eat each other.
Then scientists detected
the faint echoes
of actual ripples
in space-time.
When engineers turned on
the laser interferometer
gravitational-wave observatory,
or LIGO for short,
they immediately picked up
the faint signal
of gravitational waves.
Gravitational waves are created
by huge explosions in space.
To make them, you need an almost
unimaginably energetic event,
something really, really big...
...something like
merging black holes.
A black hole merger
is the most violent,
the most energetic thing
that happens
in the universe, period.
Picture the scene,
1.3 billion years ago.
Two black holes circle each
other in a dance of death.
The larger black hole
pulls the smaller one inwards
until they're locked together
in a spiral.
Very, very slowly,
that orbit is decaying.
They're getting closer
and closer and closer.
And then they will merge
into one giant black hole,
truly one of the most dramatic
events in the universe.
Finally, they collide
in one of the largest bangs
since the big bang.
I would have loved
to have been able
to safely view the collision
of these two
black holes up close.
Imagine these two black holes
as they spiral
in toward each other,
going faster and faster
and faster and faster.
And then, suddenly, where
there appears to be nothing
or just distortions in space
in front of you,
suddenly, there is this
enormous burst of energy.
And everything
just rains around you.
By measuring the frequency
we can calculate the size
of the objects causing them.
When those two black holes,
weighing 29 solar masses
and 36 solar masses, collided,
they created a black hole
around twice the size.
In some ways,
it's very elegant and simple.
You take two black holes.
You spiral them in together.
And you end up
with one big black hole.
The event showed that black
holes can double their mass
through cannibalism... Almost.
The final black hole was less
than the sum of its parts.
There were 3 solar masses
missing.
That may not sound like a lot.
So let's put it in context.
Our sun is burning
about 100 billion
hydrogen bombs every second.
And over its
10-billion-year lifetime,
it will convert less
than maybe 1% of the mass
of the Sun to energy.
In 2/10 of a second,
3 times the mass
of the Sun in matter
got converted to energy
in that collision.
It was 36 septillion yottawatts.
What does that mean?
A lot of freaking energy.
That's more energy
in that 2/10 of a second
than is emitted by all the stars
in the visible universe
in the same time.
In its first run,
LIGO detected two collisions.
This suggests
that cannibal black holes
are relatively common
and that each feast
builds a larger black hole.
But so far,
the largest black hole
these mergers have produced
is 62 solar masses,
not close to the largest
supermassives we've found.
It's hard to imagine,
in 13.8 billion years,
that there'd be enough
collisions of 30-solar-mass
black holes to build up to form a
billion-solar-mass black hole.
That's 100 million collisions.
So maybe small
black holes eating each other
isn't the solution.
Maybe supermassive black holes
are eating each other.
If so, could
the supermassive black hole
at the heart of our own galaxy
be on the menu?
We've found
supermassive black holes
so large, they defy explanation.
They're too big to have grown
by simply eating
the matter around them.
They can't form the same way
that regular black holes do.
There must be something else
that happens that lets them grow
to such enormous mass.
Too large to have
grown from dark stars
and too big to have grown
from regular black holes
simply eating each other.
Merging black holes
almost certainly play a role
in our understanding
of supermassive black holes.
We think that supermassive black
holes themselves also merge
and have merged regularly over
the course of the universe.
Now, whether this
merging activity itself
is enough to make them that big,
the jury is still out on that.
Now a newly discovered
type of galaxy
may provide an answer.
It's called w2246-0526.
And we can't see it.
But we can detect
the heat it gives off.
This galaxy is an example
of a rare class
of objects called hot dogs.
One of the funnier terms f
is a hot dog galaxy.
And no, this is not
some delicious sausage snack.
In fact, it means "hot,
dust-obscured galaxy."
It's called obscured
because it's shrouded
in so much dust and gas,
the only light that escapes
is infrared in the form of heat.
All this heat must be
coming from somewhere.
So in the core,
there is a cauldron,
a seething
supermassive black hole,
the likes of which
we can't even imagine.
Of all the supermassive
black holes we know of,
the ones that are obscured
in these hot dog galaxies
may be the ones
that are the most ravenous,
consuming many millions of times
the mass of the Sun.
Scientists theorize
that hot dogs
could be the offspring
of cannibal giant black holes.
When the monstrous
black holes merge,
they drag gas and dust
with them.
This brings more food
to the table,
allowing the new black hole
to gorge itself.
When you have these
two galaxies merging,
they have all-new food.
It's a brand-new dinner plate,
a brand-new buffet
of food to eat.
The combination
of cannibalism and fresh food
allows the black holes
to grow super large.
Perhaps this is how
the supermassive black hole
at the center of our galaxy
grew when it was young.
But what's the future
of our supermassive
Sagittarius "a" -star?
As far as
supermassive black holes go,
Sagittarius "a" -star
is actually still kind of
in the minor leagues.
It's small.
But it's not done yet.
It's still eating.
It's still growing.
And in around 4 billion years,
it's going to become
25 times larger,
because it's going to be
eaten by its neighbor.
The giant Andromeda galaxy
is heading our way.
And it's going to engulf
our milky way.
When galaxies merge,
their central supermassive
black holes merge.
Andromeda's huge
supermassive black hole
will drag Sagittarius "a" -star
into orbit...
...gradually drawing it closer
and closer
until it devours it.
The new supermassive
black hole will weigh
around 100 million solar masses.
But the disruption
to the new galaxy
will provide the new
supermassive black hole
with plenty to eat
and the opportunity to grow
a whole lot bigger.
At present,
there are many theories
of how supermassive
black holes get so big.
Most likely, it's a
combination of them all.
But however it happens,
we can be pretty sure
it's one of the most spectacular
things in the universe.
The jury's still out on exactly
how supermassive black holes
become so massive.
Making all
the black holes we see
probably requires
a pretty diverse cookbook.
So any physicist who's looking
for a really simple,
single answer
for how they get made,
they're probably
gonna be disappointed.
It's probably a pretty complex
thing that's going on.
It could be through eating.
It could be through
eating and merging.
And usually, the answer
is somewhere in the middle.
So they will merge
with other black holes.
And they'll also have
a few snacks between mergers.
circle each other
in a dance of death.
They spiral inwards,
their immense gravities
pulling them ever closer.
When they finally collide,
it's one of the most
powerful events
since the big bang.
This explosive mystery
sends ripples
across the world of science.
But can it also answer
one of the most pressing
questions in cosmology?
How do supermassive
black holes grow so large?
Captions paid for by
Discovery communications
In the known universe,
there are roughly
2,000 billion galaxies.
Each one has a different
shape and size.
But they may all have
one feature in common...
a supermassive black hole
buried at their center.
As its name says,
it is supermassive.
And here, we're talking
about objects
that are millions
or billions of times
the mass of the Sun.
Supermassive black holes
are so big
that we need a special scale
for measuring them.
A solar mass
is the mass of the Sun.
So when we study the universe,
we have to use the tools
that we have in hand.
And what's the most massive
thing that we have around us?
It's the Sun.
And so we refer to things
in multiples
of the mass of the Sun
because it just makes it easier
to wrap our heads around.
However, if you have something
that's 17 billion times
the mass of the Sun,
that's pretty difficult
to wrap your head around anyway.
But we know that those
kinds of black holes
live in the centers of galaxies.
The supermassive black hole
the milky way, is called
Sagittarius "a" -star.
It weighs in
at 4 million solar masses.
But compared to the other
supermassive black holes
out there, it's puny.
This is probably
one of the only contexts
where you would think that
our supermassive black hole
isn't very supermassive.
The supermassive black hole
in our neighboring galaxy,
Andromeda,
is 25 times larger
than Sagittarius "A" -star,
coming in at
100 million solar masses.
But compared
to the largest monsters
out in the universe,
it's a runt.
O.J. 287's primary
supermassive black hole
weighs in
at 18 billion solar masses.
And the black hole
in the core of galaxy NGC 4889
in the coma cluster
weighs 21 billion solar stars.
That's over 5,000 times larger
than Sagittarius "a" -star.
These are incredible things
that are more massive
than some galaxies.
Now astronomers may have ma
a giant, new
supermassive black hole
that's a mind-blowing
30 billion times
the mass of the Sun.
It's a huge puzzle.
And we have simply no idea
how it got so big.
It's a huge mystery how black
we started finding
black holes with millions
and billions of times
the Sun's mass.
No one expected that.
And we have no idea
how they got to be so big.
It's not entirely
clear at this point
how supermassive black holes
can get to be the masses
that they are today.
Regular-sized black holes form
when large stars over 20 times
the mass of our sun
crash and burn.
When a large star
runs out of fuel,
the core stops generating
enough outward force
to counteract the power
of gravity crushing inwards.
As the star collapses,
the outer part explodes
in a supernova.
The inner core shrinks
from a sphere
millions of miles wide
to one just 10 miles across.
It's like shrinking
the earth down
to the size of a golf ball.
This rapid collapse
creates a black hole.
So we now have seen black holes
that are solar-mass black
holes
and black holes that are million
or billion-solar-mass
black holes.
And the question is, how do you
get from one to the other?
Do the giants somehow grow
from a solar-mass black hole?
One of the big puzzles today is,
how do you make one of these
supermassive black holes?
One idea is,
you get there by starting
with a solar-mass black hole,
having it grow through a stage
of being an intermediate-mass
black hole
and then eventually
getting to be
a supermassive black hole.
Theoretically,
intermediate-mass black holes
should be between 100
and 100,000 solar masses.
But we've never seen one.
Part of the mystery
of supermassive black holes
is that black holes seem
to occur in two flavors.
You have ones that are
only a couple times
the mass of the Sun.
And you have ones
that are millions
or billions of times
the mass of the Sun.
So we have small
and extra large.
If we think
of the stellar-mass black hole
as sort of the baby black holes,
and the supermassive black holes
as the grown-up black holes,
we're missing
the teenage black holes.
Where are these black holes
that have masses
that are between stellar mass
and supermassive?
They're sort of like
a holy grail
for black hole hunters.
Where are these things?
Where can we find them?
And how do you make them?
Then astronomers caught a break.
They picked up a burst of energy
coming from the NGC 1399 galaxy.
It was the death throes
of a star being eaten
by a black hole.
When they measured its size,
they discovered it was
an elusive intermediate-mass
black hole.
The missing link had been found.
But when scientists did the math
to see if such an
intermediate-mass black hole
could grow into
a supermassive black hole,
they hit a snag.
There hasn't been enough time
since the birth of the universe
for an intermediate-mass
black hole
to eat enough stars
to grow into
a supermassive black hole.
It doesn't seem like
there's enough time
for black holes to get
as big as we see them.
But supermassives
are everywhere we look.
How did they get there?
And how did they grow so huge?
In our universe, we've
detected small black holes.
And we've seen monsters,
supermassive black holes
billions of times
the mass of our sun.
But we'd found
almost none in between.
So how do you get from a small
black hole to a giant one?
One of the most important
outstanding questions
in cosmology is,
how did supermassive black holes
get as big as they are?
And when did that happen?
Black holes are normally S
an all-you-can-eat buffet.
One of the best ideas
for how black holes grow
is that black holes do
what we expect
black holes to do,
and that is eat stuff.
For a black hole,
it's almost as if the universe
is its restaurant.
And on its menu,
you'll find stars, planets,
and clouds of gas and dust.
So is binge-eating the answer
to growing
a supermassive black hole?
Theoretically, black holes
should keep on growing forever
as they consume
more and more food.
But recent discoveries suggest
that the universe
puts them on a diet,
controlling how much they eat.
Black holes are hungry.
They like to eat.
But sometimes,
they eat too much,
and they burp it up.
February 2015.
Astronomers report
something unusual
in the galaxy NGC 2276.
It looked like something
had taken a bite
out of one of its spiral arms.
Sitting alone in the void
was an intermediate-mass
black hole,
about 50,000 times
the mass of the Sun.
One theory
was that the black hole
had eaten everything around it,
creating the dead zone.
But the detection
of a burst of energy
from the black hole suggests
it may have tried
to eat too much
and, in the process,
destroyed its food source,
burping so hard,
its food was blasted away.
Turns out that black holes
are actually very messy
a lot of matter gets thrown
off as it tries to absorb it.
So things move in, gets hot.
But then a lot of it gets
thrown all the way back out.
Black holes
are not vacuums in space.
They do not just eat
everything around them.
And so they are messy.
Some things get in.
And they take that on.
And it grows their mass.
And some things are just
flung out as they're eating.
The enormous gravity of black
holes sucks gas, dust,
and even stars towards them.
Everybody's been to
an all-you-can-eat buffet.
But let's be honest.
There really is a limit
to how much you can eat.
Black holes
are gluttons. They're greedy.
They don't really know
when they've eaten too much.
They just keep on cramming in
more and more food.
It doesn't just fall in.
It has to go down the drain,
more or less.
And so it forms this disk
around the hole.
And as it does that,
there's a lot of turbulence
and magnetic fields
and a witch's brew of forces
going on there
that get it really hot.
As the gas
and dust swirls around,
it heats up,
pushing temperatures to
millions of degrees Fahrenheit.
This swirl, called
the accretion disk,
also generates powerful
magnetic fields.
These fields are dragged
by the SPiN of the black hole
and become focused
above the poles.
As energy builds up,
the magnetic fields
become so compressed
they blast out
super-energized particles.
These beams can actually
be incredibly violent.
Matter is flung out
at a large fraction
of the speed of light.
It's a tremendous wind
that blows very hard away
from the black hole.
The jet hits the gas clouds
surrounding the black hole,
blowing the buffet away.
If they eat too much,
they can basically
blow everything
that's in their vicinity away.
They lose their food supply.
And then they're gonna starve.
They can kind of shoot
themselves in the foot.
With no food available,
the black hole stops growing.
Astronomers think
that's what happened
to the intermediate-mass
black hole
they discovered
in the dead zone.
These burps may
regulate star formation
and stop the black hole
from getting obese.
But over time,
the black hole
will start eating again
as gas falls back towards it.
But can an intermediate-mass
black hole eat enough
to become
a supermassive black hole
weighing billions
of solar masses?
Could that black hole
become so obese by eating?
That's a really
interesting question.
You'd have to eat
a heck of a lot
to get that fat.
When you think about it, if
you imagine an average galaxy
has 100 billion stars,
the black hole
would have to eat one
in every five stars
in the galaxy.
The universe is old.
But is it really old enough
that black holes have had time
to consume billions of stars?
That seems kind of unlikely.
It doesn't seem to add up.
We need some other way
to make these
supermassive black holes.
And the question is,
what is that?
Maybe we've been making
this all too complicated.
Maybe to get a big black hole is
to start big in the first place.
So how can black
holes start big?
To answer that question,
scientists had to journey back
to the very start
of the universe,
to a mysterious time
called the dark ages.
As we look out
into the universe,
we're seeing farther
and farther back in time.
We have now looked back
over 12 billion years
to the time when the cosmos
was still an infant.
And what we found
was a huge surprise.
We had made the assumption
that as you look farther
out into the universe,
the black holes
would be smaller.
They haven't had
much time to grow.
But now we've found
a 12-billion-solar-mass
black hole that's actually less
than a billion years
into the universe.
How did this thing
form so early?
How did it grow so fast?
This is like walking
into a delivery room
and finding a 100-pound baby.
I mean, how does that
even happen?
It doesn't make any sense.
Physics tells us no black hole
could swallow enough stuff
to get that big that quickly.
There really wasn't enough
time between the big bang
and when we're
studying these things
for them to grow
to such large sizes
just by eating
matter around them.
So if there's not enough time
maybe they're born supermassive.
To understand how, we have
to travel back even farther,
to not long after
the birth of the universe.
The early universe
was definitely
a much more compact
and richer place for material.
It was smaller,
and it was denser.
Things were much closer.
It was hotter.
It was just a much
more intense place to be.
Clouds of hydrogen and
helium gas clumped together.
As the clouds grew,
so did their gravity,
sucking in more and more gas.
Eventually, the ball of gas
became so dense, it collapsed,
triggering nuclear fusion.
A star was born.
These massive first stars
are called population III stars.
Because there was
so much food around,
these stars were huge,
many times bigger than
any stars that exist today.
We think a lot of these
population III stars
probably were
incredibly massive,
incredibly short-lived,
and just blew up right away.
They would've left massive
black holes behind.
With so much food available,
these young, ravenous
black holes, called quasars,
started binge-eating
and became incredibly bright.
Billions of years later, we
can still see their gluttony.
The most luminous,
bright objects in the universe
are things called quasars.
And it may seem kind of ironic.
But what these really are
are supermassive black holes.
There's so much stuff
trying to cram itself down
the black hole that everything
gets very hot, very energetic.
And you can see them
clear across the universe.
But when we measured
the size of the young quasars,
we discovered they were already
billions of solar masses.
There's not enough time,
a billion years after
the universe was created,
for them to get to
a billion solar masses in...
it's just too short a time.
So the question becomes,
that are this big
in that small amount of time?
We need some other way
of growing these
supermassive black holes.
There needs to be
some other mechanism
that allows them
to get that massive so early.
But what is that?
A clue can be found
in the very early universe.
The early universe is still
so much of a mystery to us.
We know that conditions
were very different.
It was denser.
There was a lot more material.
This period
is called the dark ages.
During the dark age, we know
that there was
basically nothing happening.
Matter existed.
We think that there
was hydrogen and helium gas
but really not much else.
There were a few stars around,
but nothing large enough
to form giant black holes.
But there were
huge clouds of gas.
And because the universe
was much smaller and denser,
the clouds were much thicker.
The idea is that
from these basic ingredients,
gravity and gas,
the cosmos built
massive black holes.
Somehow, the universe
has created a shortcut
to the black hole.
We've typically
thought of it as,
cloud of gas
collapses into a star,
star evolves, star dies,
leaves behind a black hole.
Perhaps the universe
has found a way
to skip the star phase
and go directly
to the black hole.
Clouds of gas may have
built massive black holes
in a process
called direct collapse.
As they collapsed,
they never even formed a star.
They just collapsed straight
into a giant black hole.
Through this direct
collapse theory,
you can form really
big black holes.
Imagine what it's like seeing
one of these giant clouds
of gas collapsing down
into a black hole.
You might think
you start with, okay,
cloud of gas slowly collapsing,
and, boop, it's a black hole.
That wouldn't be the case.
It would be more like
giant cloud of gas
starts collapsing,
then... aah! Black hole.
It's believed
that direct collapse
could have created black holes
up to a million times
the mass of the Sun,
much bigger
than from the collapse
of a single star.
These early black holes
are sort of like the galaxies
that never were.
They were gonna make galaxies.
But instead, they collapsed
into very massive black holes.
For direct collapse
to form a black hole,
the conditions need
to be precise.
The clouds must be
very symmetrical,
forming a smooth ball.
If you have a ball of gas
that isn't quite a ball,
that's not quite homogeneous,
as it collapses, it'll fragment.
And it'll fragment into objects
that won't form black holes.
So you want it to be hot enough
that it stays
one big, giant thing.
But it does need to cool
a little bit, right,
so that you get it
to collapse in on itself.
You have to get
uniform collapse over time
of a very large amount
of hydrogen gas, presumably,
which is the original matter
in the universe,
collapsing spherically
symmetrically,
without fragmenting,
over a period of less
than 500 million years.
Direct collapse
may have created black holes
a million times
the mass of the Sun.
But it can't completely explain
the 12 billion solar-mass
supermassive black holes
we see in the early universe.
Maybe gigantic supermassive
black holes were created
by strange, unseen forces.
Maybe they were created
by the mysterious dark universe.
Astronomers looking
deep into the early universe
have discovered gigantic
supermassive black holes.
This is a pretty deep mystery.
There are these
supermassive black holes
that exist
in the very early universe.
And by all accounts,
they should not exist.
According to
the normal laws of physics,
it shouldn't have been possible
for them to grow so big
so quickly.
For astrophysicists,
understanding how black holes
have grown to be so large is
one of our biggest mysteries.
We need some other way
of growing these
supermassive black holes.
There needs to be
some other mechanism
that allows them
to get that massive so early.
But what is that?
Everything we can see
in the night sky
makes up just 4.8%
of all the matter in the cosmos.
The rest is the dark universe,
including dark matter.
We can't see it, feel it,
or detect it directly.
But we know dark matter
is there.
Its gravity is tugging
on everything around it.
And we're beginning
to understand
it plays a fundamental role
in the formation
of the universe.
Most of the stuff
that collects together
gravitationally is dark matter.
So perhaps black holes form
somehow with the inclusion
of dark matter.
One way of looking at it
is there's six times
as much dark matter
as normal matter.
So there's six times
as much food out there
for the black holes to eat
if they're able to tap
into this dark stuff.
Maybe these supermassive
black holes are growing
by eating dark matter.
There are
some tantalizing clues.
The largest supermassive
black holes
don't live in the galaxies
with the most regular matter.
They live in the galaxies
with the most dark matter.
The one thing we know
about dark matter right now
is that it has gravity.
And a black hole runs
on gravity.
It attracts anything with mass.
So there's no reason to assume
that black holes would
only eat regular matter.
And now we know that there's far
more dark matter out there.
Maybe dark matter
helps the black holes eat.
Maybe in some ways,
dark matter is a feeder
for these supermassive
black holes.
Perhaps what really grows
a supermassive black hole
is all of the regular matter
being directed into the center
by the dark matter around it.
Maybe the dark
matter's powerful gravity
sucks in regular matter
and funnels it
into the black hole.
In a sense, the dark
matter is greasing the wheels.
It's sort of tilting
the table up
so that that food can
slide right in.
But now scientists
think the dark matter
may create gigantic
black holes directly
by igniting dark stars.
Some believe that dark matter
sparked early universe
super stars.
When they die, they leave behind
supermassive black holes.
Dark stars sound like
they come from
the fertile imagination
of some Sci-Fi writer.
But Dr. Katie Freese believes
they may explain
how early supermassive
black holes grew so fast.
Dark stars are amazing.
So, when we first had this idea,
we got excited really quickly,
because this is
a new type of star
that has never been seen before.
Dark stars may have
been some of the first stars
to form in the universe.
They sparked into life
when the universe was just
200 million years old.
But how could dark stars form
really massive black holes?
A newborn black hole can't weigh
more than its parent star.
So in order to give birth to
a really massive black hole,
the parent star has to be
supermassive, as well.
These early objects
are really strange.
They're very cool.
And they're really, really big.
The size of these things
is 10 times the distance
between the Sun and the earth.
But how is that possible?
Regular stars have
an upper size limit.
A star is a battle between
gravity pushing inwards
and nuclear fusion pushing out.
When the star grows too big,
its gravity
becomes overwhelming.
The delicate balance
between gravity
and fusion is broken.
Gravity wins out,
and the star collapses.
But dark stars
may have a work-around
that lets them
become supermassive.
So, they are made
of ordinary matter.
They're made
of hydrogen and helium.
But they're powered
by dark matter.
We don't know what
dark matter is made from.
But we do have theories
on how it might power a star.
One of the best ideas
we have for dark matter
is that it's made of weakly
interacting massive particles,
or wimps for short.
So, these wimps are
their own antimatter.
And that means, whenever
they encounter each other,
they annihilate and turn
into something else.
That means a lot of heat
is released, a lot of energy.
And it's that energy
that could power stars.
The energy
from the wimps' annihilations
keeps the star from
collapsing like a normal star.
So it's possible
that, in some stars,
their internal reactions
are actually being powered
by dark matter.
If that's the case, then you
could imagine situations
where, when that burns out,
you produce very massive
black holes.
So it could be that dark matter,
the physics of dark matter,
plays really important roles
in creating black holes
and their prevalence
in the universe.
The energy from the dark matter
allows the dark stars
to grow huge.
When they first form,
they're small.
They're about the mass
of the Sun.
But because they're so cool,
they keep accumulating matter
and growing, growing, growing.
And some of them will get
to be a million times
as massive as the Sun
and a billion times as bright.
But these giants
don't live for long.
Eventually,
the dark matter particles
wipe each other out completely.
And there is no more fuel
to keep the massive amount
of ordinary matter
from collapsing.
And then that's it.
There's nothing to sustain
this big, puffy object.
If it's big enough, you collapse
directly to a black hole.
A monster
supermassive black hole.
It's really fun
to think about the possibility
that the physics of dark matter
is actually helping
to power stars.
If so, it would bring, you know,
a whole new window
into our understanding
of stars and their evolution.
At the moment, dark stars
are just theoretical.
But when the powerful
James Webb telescope
comes online in 2018,
we may get our first glimpse.
We're gonna do an observing
run and look f
and so we're very excited.
If you would find an entirely
new type of star,
that would be huge.
While Katie Freese
looks for dark stars,
another team is investigating
another radical idea
that offers new insight
into how supermassive
black holes grow so huge.
They detect the faint echoes
of a violent event
from across the universe,
the remnants of
an extraordinary collision,
a supremely energetic event
that reveals
black holes are cannibals.
Our universe
is filled with enormous
supermassive black holes
that defy explanation.
Supermassive black holes
are one of the things
in the universe that,
when you run the physics,
when you run the math
of how did they evolve,
they really shouldn't be there.
It's still a profound mystery.
The universe hasn't
been around long enough
for regular black holes
to eat enough matter
to get supermassive.
So how did they get so big?
The most logical answer
is that large black holes
are born large,
around 1 to 2 billion
solar masses.
But that's still
over 10 times smaller
than the largest supermassive
black holes out there.
Given the time scales, it
doesn't seem to add up.
We need some other way
to make these
supermassive black holes.
And the question is,
what is that?
A clue came
from a large, isolated galaxy
200 million light-years away
in a quiet part of the universe.
Nestling alone was
a supermassive black hole
with a mass of 17 billion suns.
Normally, such monsters
are found in dense regions
of space
with lots of galaxies
and lots of stars.
This black holes doesn't match
its surroundings at all.
It's kind of like driving
to the middle of a desert
and coming across
the empire state building.
Now, the empire state building
belongs in the middle of a city.
And a black hole this big
belongs in a rich cluster
of galaxies.
This is the first time
astronomers have found
such a giant object
lurking in such a relatively
empty area of the universe.
So you got to ask the question,
if there's nothing else around,
how exactly do you grow
a 17-billion-solar-mass
black hole?
One possible answer
is the stuff of nightmares.
Maybe the story
of this black hole
is actually a little more
scary than we thought.
Maybe it's all alone
because it ate
all of its neighbors.
Maybe it was eating
more than galaxies.
Maybe it was eating
its own kind.
The thing about black holes
is they're omnivores.
They'll eat anything.
Anything that gets close them,
they'll gobble up.
One way black holes
can grow so large
is by eating other black holes.
So in a sense,
they may be cannibals.
Cannibal black holes
were just theoretical.
We'd never actually
seen them eat each other.
Then scientists detected
the faint echoes
of actual ripples
in space-time.
When engineers turned on
the laser interferometer
gravitational-wave observatory,
or LIGO for short,
they immediately picked up
the faint signal
of gravitational waves.
Gravitational waves are created
by huge explosions in space.
To make them, you need an almost
unimaginably energetic event,
something really, really big...
...something like
merging black holes.
A black hole merger
is the most violent,
the most energetic thing
that happens
in the universe, period.
Picture the scene,
1.3 billion years ago.
Two black holes circle each
other in a dance of death.
The larger black hole
pulls the smaller one inwards
until they're locked together
in a spiral.
Very, very slowly,
that orbit is decaying.
They're getting closer
and closer and closer.
And then they will merge
into one giant black hole,
truly one of the most dramatic
events in the universe.
Finally, they collide
in one of the largest bangs
since the big bang.
I would have loved
to have been able
to safely view the collision
of these two
black holes up close.
Imagine these two black holes
as they spiral
in toward each other,
going faster and faster
and faster and faster.
And then, suddenly, where
there appears to be nothing
or just distortions in space
in front of you,
suddenly, there is this
enormous burst of energy.
And everything
just rains around you.
By measuring the frequency
we can calculate the size
of the objects causing them.
When those two black holes,
weighing 29 solar masses
and 36 solar masses, collided,
they created a black hole
around twice the size.
In some ways,
it's very elegant and simple.
You take two black holes.
You spiral them in together.
And you end up
with one big black hole.
The event showed that black
holes can double their mass
through cannibalism... Almost.
The final black hole was less
than the sum of its parts.
There were 3 solar masses
missing.
That may not sound like a lot.
So let's put it in context.
Our sun is burning
about 100 billion
hydrogen bombs every second.
And over its
10-billion-year lifetime,
it will convert less
than maybe 1% of the mass
of the Sun to energy.
In 2/10 of a second,
3 times the mass
of the Sun in matter
got converted to energy
in that collision.
It was 36 septillion yottawatts.
What does that mean?
A lot of freaking energy.
That's more energy
in that 2/10 of a second
than is emitted by all the stars
in the visible universe
in the same time.
In its first run,
LIGO detected two collisions.
This suggests
that cannibal black holes
are relatively common
and that each feast
builds a larger black hole.
But so far,
the largest black hole
these mergers have produced
is 62 solar masses,
not close to the largest
supermassives we've found.
It's hard to imagine,
in 13.8 billion years,
that there'd be enough
collisions of 30-solar-mass
black holes to build up to form a
billion-solar-mass black hole.
That's 100 million collisions.
So maybe small
black holes eating each other
isn't the solution.
Maybe supermassive black holes
are eating each other.
If so, could
the supermassive black hole
at the heart of our own galaxy
be on the menu?
We've found
supermassive black holes
so large, they defy explanation.
They're too big to have grown
by simply eating
the matter around them.
They can't form the same way
that regular black holes do.
There must be something else
that happens that lets them grow
to such enormous mass.
Too large to have
grown from dark stars
and too big to have grown
from regular black holes
simply eating each other.
Merging black holes
almost certainly play a role
in our understanding
of supermassive black holes.
We think that supermassive black
holes themselves also merge
and have merged regularly over
the course of the universe.
Now, whether this
merging activity itself
is enough to make them that big,
the jury is still out on that.
Now a newly discovered
type of galaxy
may provide an answer.
It's called w2246-0526.
And we can't see it.
But we can detect
the heat it gives off.
This galaxy is an example
of a rare class
of objects called hot dogs.
One of the funnier terms f
is a hot dog galaxy.
And no, this is not
some delicious sausage snack.
In fact, it means "hot,
dust-obscured galaxy."
It's called obscured
because it's shrouded
in so much dust and gas,
the only light that escapes
is infrared in the form of heat.
All this heat must be
coming from somewhere.
So in the core,
there is a cauldron,
a seething
supermassive black hole,
the likes of which
we can't even imagine.
Of all the supermassive
black holes we know of,
the ones that are obscured
in these hot dog galaxies
may be the ones
that are the most ravenous,
consuming many millions of times
the mass of the Sun.
Scientists theorize
that hot dogs
could be the offspring
of cannibal giant black holes.
When the monstrous
black holes merge,
they drag gas and dust
with them.
This brings more food
to the table,
allowing the new black hole
to gorge itself.
When you have these
two galaxies merging,
they have all-new food.
It's a brand-new dinner plate,
a brand-new buffet
of food to eat.
The combination
of cannibalism and fresh food
allows the black holes
to grow super large.
Perhaps this is how
the supermassive black hole
at the center of our galaxy
grew when it was young.
But what's the future
of our supermassive
Sagittarius "a" -star?
As far as
supermassive black holes go,
Sagittarius "a" -star
is actually still kind of
in the minor leagues.
It's small.
But it's not done yet.
It's still eating.
It's still growing.
And in around 4 billion years,
it's going to become
25 times larger,
because it's going to be
eaten by its neighbor.
The giant Andromeda galaxy
is heading our way.
And it's going to engulf
our milky way.
When galaxies merge,
their central supermassive
black holes merge.
Andromeda's huge
supermassive black hole
will drag Sagittarius "a" -star
into orbit...
...gradually drawing it closer
and closer
until it devours it.
The new supermassive
black hole will weigh
around 100 million solar masses.
But the disruption
to the new galaxy
will provide the new
supermassive black hole
with plenty to eat
and the opportunity to grow
a whole lot bigger.
At present,
there are many theories
of how supermassive
black holes get so big.
Most likely, it's a
combination of them all.
But however it happens,
we can be pretty sure
it's one of the most spectacular
things in the universe.
The jury's still out on exactly
how supermassive black holes
become so massive.
Making all
the black holes we see
probably requires
a pretty diverse cookbook.
So any physicist who's looking
for a really simple,
single answer
for how they get made,
they're probably
gonna be disappointed.
It's probably a pretty complex
thing that's going on.
It could be through eating.
It could be through
eating and merging.
And usually, the answer
is somewhere in the middle.
So they will merge
with other black holes.
And they'll also have
a few snacks between mergers.