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.

Energy so powerful they can incinerate planets and rip stars to pieces.

These are among the most mysterious and most energetic phenomena 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.

For decades, astronomers have observed brilliant points of light in the night sky.

But there was something strange about them.

They look 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 3C273 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 has

been the biggest atomic bomb that has ever exploded.

We're aware of quasars out there that are putting out more energy than one 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 and dense enough.

A black hole.

That is the only thing that we know of in the Universe that could power a quasar.

Stars 25 times more massive than our sun eventually lose their lifelong battle against gravity.

They suffer a catastrophic collapse, and 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 into 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 the 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 normal, three times more massive than our sun, to super sized.

Super massive, 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 black holes' enormous gravity.

And scientists think that only super massive black holes are able to provide the energy to power quasars.

Yet quasars can 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 called the accretion disk.

You can think of it as a giant whirlpool of matter that's trying to fall onto this super massive 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 the secretion 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.

For decades, quasars have been baffling astronomers.

And weirdly, it now seems that even the brightest objects can remain unseen.

But you know what you can't see?

The brightest galaxy we've discovered so far.

November 2015.

Astronomers used the Atacama Large Millimeter Array, Alma, to peer inside the brightest galaxy in the Universe.

A quasar named W2246 emits as much light as 350 trillion suns.

But to our eyes, it's invisible.

And that's because it emits in the infrared.

It's not a normal galaxy, it's a hot dog galaxy.

Hot dogs, hot dust-obscured galaxies, are surrounded by clouds of interstellar

dust, so the incredible light from this quasar is hidden from view.

Because a quasar is a super massive black hole that has stuff around it falling in,

you can imagine that sometimes there's so much stuff around the black hole,

the quasar is completely obscured.

The quasar's visible light is absorbed by the thick layers of dust.

But what does escape is lower energy, infrared light.

And at this wavelength, it's staggeringly bright.

The cool thing about hot dogs, besides their name, is that they weren't expected.

We're finding that half of the most luminous quasars in the Universe are hot dogs.

Quasars are so bright that some are visible from the very edge of the Universe, over 13 billion light years away.

That means they burst into life less than a billion years after the Big Bang.

But how could such monsters exist so soon after the birth of the Universe?

We have discovered stunningly luminous quasars across the Universe that are brighter than their whole galaxies.

And that light has been travelling 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.

In 2017, scientists at the Las Campanas Observatory in Chile focused their

telescopes on the most ancient part of the Universe and got 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 formed around 700 million years after the Big Bang, when the Universe was mostly a soup of hydrogen and helium gas.

We know quasars are powered by super massive black holes.

But discovering a black hole this big, so early in the evolution of the cosmos,

is a huge mystery.

One of the big questions we have in astronomy is how did these super massive 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 galaxies.

That means 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 and 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 consumes everything that gets too close, growing larger and larger.

However, 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, it's just too short a time.

So there has to be another process in addition to all this eating that caused the seed to form.

To swell to a billion solar masses, we now think these giants grow from smaller seed black holes.

We know that black holes usually form from exploding stars of around 25 solar masses or greater.

And that's quite small.

To be born super massive, you need a super massive star, a stellar giant,

born from the primordial gases of the early Universe.

And so you have these huge clouds of mostly hydrogen, a little bit of helium,

and that's basically all that was there.

And as material cooled, it would collapse into these big, big stars of just balls of hydrogen and space.

These super giant stars lived fast and died young.

When they died, they formed these seed black holes.

So that's one way you could get a massive seed is that you just have the earliest

stars collapsing into a black hole when they died.

But there's a problem.

It seems even these super massive stars couldn't have produced big enough seed black holes.

There has to be another way to generate a billion solar mass black hole in less than a billion years.

How else could the Universe create super massive black holes from just thick clouds of gas?

One theory of how you get these super massive black holes is that you just have one big collapse event.

We call it direct collapse.

It's only a theory.

But we think this is how direct collapse would work.

Huge superdense clouds of hydrogen gas clump together.

Gravity then builds up and drags in more gas, which becomes more and more dense,

until the gas collapses under its own weight.

Instead of forming a star, it crushes down straight to a super massive black hole.

Then a galaxy starts to form around the giant.

Gas streams towards the center, getting hotter and hotter, until a quasar explodes into life.

And these are so bright, we can see them today 13 billion light years away.

All of these are ideas right now.

Theorists are working really hard to make these models work.

Finding more and more distant quasars will teach us what those seeds are that form into the quasars.

It might teach us some new physics to create these big black holes that quickly.

The more we investigate quasars, the more we discover about the early Universe and the galaxies within it.

Galaxies that appear calm and peaceful places.

Yet closer inspection reveals extreme violence.

And huge scars extending from their centers out tens of thousands of light years.

What could have caused such devastation?

This is galaxy cluster Hydra A.

Here are the scars.

And when viewed in multiple wavelengths, the cause was revealed.

Two colossal jets of energy blasting out from the galactic core, shooting out from the heart of a quasar.

They tear through the galaxy and out into space, creating voids in the surrounding gas.

The amount of energy in these jets is staggering, soul-crushing,

mind-destroying.

Think about how much energy is wrapped up in these quasar jets.

Something can take many, many times the mass of the Sun, accelerate it to speeds