How the Universe Works - Eleventh Season

You might have seen a boxing match on TV.

Maybe you've even seen one live.

But you have never seen a contest like this.

Take your ringside seat to the fight of the cosmos.

This is gonna be a wonderful fight to witness.

But you'll want to be a few

million billion light-years away.

It's like being punched by the ghost of Muhammad Ali.

You don't even see it coming.

Our fighters don't float like a butterfly or sting like

a bee, but they can deliver the ultimate knockout blow.

It is a soul-chilling, mind-crushing amount of energy.

It's just unbelievable.

It's a fight between two supermassive black holes.

Forget about the world heavyweight championships.

This is the universe's heavyweight championships.

Get ready for the heavyweight

championship of the universe.

2021, scientists detect

a gigantic rumble deep in space,

a tsunami of gravitational waves,

giant ripples racing across the universe.

Gravitational waves that big have to

come from a giant, cataclysmic event.

The universe is immense and full of very

violent events that are happening every single day.

The universe is a scary place.

There is violence everywhere we look.

The growls and roars are clues about

the ultimate cosmic brawl,

the most violent event in the universe.

But we don't know where they're coming from.

Imagine a storm is coming

in the middle of the night.

You can't see the storm,

you can't see the lightning, but you can hear that rumble of

the distant thunder, and you know that it's coming.

This distant rumble of gravitational waves

is like the footwork of heavyweights

pounding the canvas of the boxing ring.

The waves are caused by something massive

throwing its weight around.

It's not the first time we've detected gravitational waves.

Our experiments have picked up

the signal of two small stellar mass

black holes colliding.

These waves are high-pitched and ring like a boxing bell.

The deep space growl is a much lower frequency,

like the roar of a crowd.

The difference in frequencies

would be even more exaggerated than the difference

between a sparrow chirping and the sound coming from

a blue whale underwater.

It would be orders of magnitude more different than that.

The low frequency of the deep space rumble

tells us that the waves are colossal.

Imagine throwing a stone in the water

and watching the little ripples come out.

Now imagine throwing in a boulder a billion times

more massive

and watching the huge waves that come from that.

Those are the waves that we're looking at.

These are more difficult to detect,

because the waves are so big.

One of their wavelengths is about 15 light-years.

You could wait for 15 years

and only have one wavelength go by the Earth.

The waves are too big for an earthbound detector

to pick up.

So, to search for the source of these giant waves,

Chiara Mingarelli and her team

use a detector already in space,

something large enough to pick up

these galactic heavyweights,

spinning dead stars called pulsars.

Our galaxy is awash with pulsars.

Now, they're called pulsars because they pulsate

very regularly... they're like cosmic lighthouses.

The lighthouse beams are so regular,

you can set your watch by them.

But when a huge gravitational wave hits them,

the timing gets knocked out of whack.

That pulsar is going to basically rock back and forth

and that's going to change the timing

of the pulses that we measure from that object.

To identify the source of the gravitational waves,

Chiara and her team measure the wobbles of 100 pulsars,

spread across light-years of space.

It's like a tsunami, and the pulsars are

like the buoys on the surface of the ocean.

And as the tsunami passes by,

we can watch all of them moving

and shifting up and down.

So our pulsar timing array

is a gravitational wave warning system.

The pulsar array has identified

the source of the tsunami of gravitational waves.

The only thing we know of that can make these

very long wavelength, very low pitch

gravitational waves would be the collisions

of supermassive black holes.

They're massive, they're huge,

and they know how to throw their weight around.

Supermassive black hole binaries produce the loudest

gravitational waves in the universe.

The gravitational wave signal revealed

something extraordinary.

It's not just gravitational waves coming

from one black hole binary pair.

It's actually from the cosmic

population of supermassive black hole binaries.

Chiara and her team think there may be

tens of thousands of heavyweight bouts going on.

Now, the scientists want to pick out the sound of one

single collision between two supermassive black holes from

the background roar.

If we were to hear

a supermassive black hole merger,

it would sound like a very low frequency growl.

This "ooooooh"

that would last about 25 million years.

To date, we haven't witnessed two supermassive

black holes trading blows in real time.

But we have seen events leading up

to the championship bout.

We've watched galaxies merge.

We've seen stars explode.

We've seen so many violent events in the universe.

But we haven't seen this one.

It's odd if you think about it.

We haven't seen the biggest one.

We haven't seen mergers between supermassive black holes.

But that may be about to change.

Chiara predicts there are 112 fighters who are

pumped up and ready to enter the ring.

In the next five years,

we should be able to detect at least one

supermassive black hole merger.

It'll be the most violent event in the cosmos.

Let's put that in context.

We talk about how supernova are some of the most explosive,

energetic things in our universe.

Well, colliding supermassive black holes

are a billion, billion, billion,

billion times more energetic than a supernova.

Think about all of the light being emitted by everything in

the universe, every star, every galaxy.

In one instant, two supermassive black holes

colliding could release 100 million times that energy.

Imagine being punched in the face by

the biggest, baddest heavyweight of all time.

Ouch.

This is way bigger than that.

Where does all this energy come from?

Surprisingly, it originates in

the smallest atoms in the cosmos,

in a story that dates back billions of years,

all the way to the birth of the universe.

We're taking our seats for

the most violent event in the universe,

the collision of two supermassive black holes.

We've never witnessed this cosmic

heavyweight championship,

but we can build up a picture of this epic fight by studying

other weight classes with lighter fighters.

2020... the earthbound gravitational wave detector,

LIGO, picks up

the distinctive signal of a stellar mass

black hole merger.

What we saw was a black hole of 85 times the mass of our sun,

and another black hole of 66 times the mass of our sun,

smashing together to create a combined black hole.

As someone who studies black hole mergers,

this was a really exciting event.

We're talking about

the largest, the heaviest, the most massive

black holes we have seen collide to date.

It may be the largest detection,

but on a universal scale,

it's still a small fry... Like lightweight boxers,

the two black holes circle each other

and emit low energy gravitational waves.

This energy loss causes the black holes

to spiral in together.

Finally, they collide in a cosmos-shattering event,

forming a single black hole

and releasing a huge blast of gravitational waves.

But when astronomers examine the single merged black hole,

something doesn't add up.

If you take the combined mass of

the two black holes, you get to 150 times

the mass of our sun.

But actually, the black hole that's left only has

a mass of 142 times the mass of our sun.

So the mass you have before the event does

not equal the mass you have after the event.

What happened to that missing eight solar masses?

The way these black hole mergers work is very roughly 5 percent

of the total mass of the system gets converted

into energy.