How the Universe Works

Mysterious lights

shine out from the edge of space,

brighter than a trillion suns.

They had to be the brightest objects

we've ever seen in the universe, putting out amounts of energy

that we couldn't possibly explain.

So powerful, they can incinerate planets

and rip stars to pieces.

These are among the most mysterious

and most energetic phenomenon in the universe.

They can destroy galaxies,

but may also be the key to their survival.

These objects are a hotbed of all kinds of crazy physics.

These celestial powerhouses are called quasars,

and we may owe them our very existence.

captions paid for by discovery communications

For decades, astronomers have observed

brilliant points of light in the night sky,

but there was something strange about them.

They looked like a pinprick of light, like a star,

and so they were really mysterious initially.

Are they a new type of star,

or something else entirely?

One of these strange objects is hiding within

the Virgo galaxy cluster.

From Earth, object 3c 273 looks just like a nearby star,

but scientists studying its light made a stunning discovery.

It was tremendously far away.

It not only was not in our galaxy,

it wasn't even in any galaxy that they could see.

It was over a billion light-years away.

If it's that far away and as bright as it was,

this must be the most luminous known object in the universe.

And this is one of the reasons these were so mysterious

for so long.

These objects are so bright that,

despite the incredible distance,

to us, they look like nearby stars.

They're called quasi-stellar objects, quasars for short.

But what are they?

With more detailed observations of quasars,

we found that they don't originate from any random place.

They always come from the core of a galaxy.

A quasar is the ultra-bright core

of an extremely distant galaxy.

The reason we can see them at all

is the result of their incredible power.

A single quasar outshines an entire galaxy,

hundreds of billions of stars' worth of energetic output,

all concentrated into a single source.

One of the most energetic events that human beings

have ever been witness to on Earth

is the biggest atomic bomb ever exploded.

We're aware of quasars out there that are putting out more energy

than 1 trillion trillion of those massive

atomic bomb blasts per second.

It is just a huge amount of energy packed into

a very, very, very small volume,

and that is almost literally unbelievable.

But if they're so small, how can they produce

such vast amounts of energy?

How can you generate something that's so bright, so energetic,

but not be very large?

What could possibly power something like that?

Hiding within a quasar

must be a very powerful engine.

What kind of object can generate that much energy,

that kind of power to create these things?

There's only one thing in the universe

that's both massive enough and dense enough...

A black hole.

That is the only thing that we know of in the universe

that could power a quasar.

Eventually, stars 25 times more massive

than our sun lose their lifelong battle against gravity.

They suffer a catastrophic collapse.

All their incredible mass is compressed

into a single point...

Giving birth to a black hole.

Black holes are totally unique.

There's nothing else like them in the universe.

They're extremely massive and dense.

They have so much mass crammed in such a small space

that they distort space a tremendous amount.

They create regions called event horizons.

The boundary of these monsters, the event horizon,

is a point of no return.

Anything that crosses that line is never coming back,

not even light.

So as light tries to freely fly through space and time,

that space and time is bent back in on itself,

and that means light can never escape.

We see black holes across the universe.

They range in mass from regular,

three times more massive than our sun,

to supersized... Supermassive, in fact.

So we think that quasars represent

the largest black holes that we see in the universe.

We're talking billions of times more massive than our sun.

It is literally almost at the edge of your ability

to perceive, right, our ability to even

think about black holes being so massive,

that they're a billion times the mass of our sun.

It's this enormous mass that leads

to their enormous gravity.

We think that only supermassive black holes

could provide the power,

but quasars outshine their entire galaxies.

Black holes suck things down. They're black.

How can they possibly be bright?

Black holes are voracious eaters.

They drag in gas and dust,

which builds up in a ring of material around the black hole.

We call this the accretion disk.

You could think of it as a giant whirlpool of matter

that's trying to fall onto the supermassive black hole.

Well, it can't all fall in at once,

and so there's a lot of friction in this disk.

This friction increases

as the motion of the gas and dust speeds up.

That could be a significant fraction of the speed of light.

If you rub your hands together at a significant fraction

of the speed of light, they will vaporize.

They will get very hot.

And so the material in this accretion disk

can actually get heated to millions of degrees.

When matter heats up, it produces radiation,

which we see as light.

The center of the galaxy shines,

visible billions of light-years away.

That's where stuff gets dense and hot,

and there, you have a quasar.

So even though black holes are the darkest objects

in the universe, they, in turn,

power the brightest objects in the universe.

Quasars are so bright,

some are visible from the edge of the universe,

or 13 billion light-years away.

That means they burst into life less than a billion years

after the big bang.

How could such monsters exist

so soon after the birth of the universe?

Across the universe,

we have discovered stunningly luminous quasars.

They're powerful, brighter than their whole galaxies,

and that light has been traveling towards us

for billions of years.

As fast as light goes, 186,000 miles per second,

it takes time to cover the vast distances between the galaxies,

so if you look out into space,

you see quasars as they were millions of years ago

or billions of years ago,

and the light has just arrived at your eyes tonight.

2017, Chile...

Scientists at the Los Campanas observatory

focus their telescopes

on the most ancient part of the universe.

They get a huge surprise.

This quasar is only about 600,

700 million years after the big bang,

and this black hole weighs about 800 million times

as much as the sun.

It's the oldest quasar ever found.

It burst into life around 700 million years

after the big bang.

Back then, the universe was mostly a soup of hydrogen

and helium gas.

We know quasars are powered by supermassive black holes,

but discovering a black hole this big so early

in the evolution of the cosmos, that's a huge mystery.

One of the big questions we have in astronomy is,

how did these supermassive black holes form?

How did they form so early in the universe?

This is an interesting mystery.

We see quasars about as far as we can see.

That means these objects existed in the very earliest galaxy.

That means a million or billion solar mass objects

were able to accumulate.

I don't think we really have a good picture

of how that can happen.

The mystery lies in how fast black holes grow.

They grow by eating at an astonishing rate.

When you eat, eventually, you get full.

You've had your last bite.

But black holes, they are never done being hungry.

They are insatiable.

A black hole eats everything that gets too close,

growing larger and larger.

But there's a limit to how fast they can grow.

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 there had to be another process,

in addition to all this eating, that caused the seed to form.

To bulk up to a billion solar masses,

we now think these giants grew from smaller seed black holes.

We know that black holes usually form from exploding stars

of around 25 solar masses or more.

That's pretty small.