How the Universe Works

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.