How the Universe Works (2010) s06e07 Episode Script

The Quasar Enigma (62 min)

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 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, 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.
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, 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.
To be born supermassive, you'd need a supermassive star, a stellar giant born from the primordial gases of the early universe.
And so you had 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 in 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 die.
But there's a problem.
Seems even these supermassive 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 supermassive black holes from just thick clouds of gas? One theory of how you get these supermassive 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, super-dense clouds of hydrogen gas clump together.
Gravity builds up, dragging in more gas, becoming more and more dense until the gas collapses under its own weight.
Instead of forming a star, it crushes down straight to a supermassive black hole.
A galaxy starts to form around the giant.
Gas streams toward the center, getting hotter and hotter, until a quasar explodes into life.
They're so bright, we can see them today, 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 the quasars, the more we discover about the early universe, but they're also revealing their destructive nature.
Recently, we've discovered galaxies with holes torn out of them.
The culprit? Death rays blasting at close to the speed of light.
The universe is full of galaxies.
From a distance, they look calm and peaceful.
Look a little closer, and you'll see evidence of extreme violence and destruction Scars extending from their centers out tens of thousands of light-years.
What could've caused such devastation? This is galaxy cluster hydra a.
Here are the scars, but viewing it in multiple wavelengths reveals the culprit.
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 near the speed of light and throw it out across hundreds of thousands of light-years.
These jets seem to launch out from the quasar's core, supercharged particles twisted into tight beams of energy, moving at millions of miles per hour, heated to trillions of degrees.
Regular quasars are seriously powerful, but quasars with jets, those are off the charts.
You're taking the power of billions or trillions of stars and focusing them into narrow jets, which basically march across the universe like death rays.
If you're too close to this thing, and you're in its way, yeah, you're not going to be in its way for long.
It's not just the galaxy and the surrounding gas that suffers.
These jets coming out are more powerful than the death star.
They would destroy not just a planet going through their path but, like, stars, whole solar systems.
This is exactly what's going on in system 3c 321.
Viewed in visible light, all we see is a pair of galaxies.
But in multiple wavelengths, we see the larger galaxy firing out a huge death ray, ripping through its smaller neighbor and out into space.
Imagine being in the direction of a jet.
If a jet's coming at you, it's over.
You're in for a deep world of hurt.
Planets would be destroyed.
Stars would explode.
These jets travel incredible distances through space.
So the largest know jet is about And a megaparsec is about So, we're talking almost from end to end.
Eventually, the jets do stop when they slam into the intergalactic medium, the thin film of gas that surrounds galaxies.
It can go hundreds of thousands of light-years, striking the intergalactic medium and setting it ablaze.
The impact sends out massive shock waves like in galaxy Pictor a.
They form these huge, puffy clouds.
They look like sort of cotton swabs.
You had a narrow jet with these big puffy things at either end.
But it seems that quasars with jets are a very rare species.
Only 10 percent have them, and no one really knows why.
The huge jets coming out of quasars are things we can see clear across the universe.
The amazing thing is we don't even really understand how they're created.
It's such a complicated process that it's hard to untangle the astrophysics going on here.
So we think that the formation of jets arises from the accretion disk, or this spinning disk of gas that's spiraling close to the event horizon of the black hole.
This is our best theory.
Gas falls towards the supermassive black hole.
It moves faster and faster, getting hotter and hotter.
When you heat gas to extreme temperatures, it becomes plasma, full of electromagnetically charged particles.
We think, in the regions around supermassive black holes, you have quickly moving charged particles.
This creates magnetic fields.
As the particles swirl around the black hole, they build up a powerful magnetic field.
The field builds up intensity and surrounds the black hole.
That strong magnetic field can wrap itself around the black hole, and any charged particles in the accretion disk will follow the paths of those magnetic fields.
And where there is a body with a magnetic field, there are magnetic poles, and that's where things can escape.
It gets wound around, spiraled up, and shoved up into a jet.
The pressures in that discuss are incredibly high, and these magnetic fields are incredibly strong, and they're wound up tightly by the spinning black hole, and what you end up with are jets that are collimated and incredibly powerful.
The jet blasts out from the poles of the black hole at 99 percent the speed of light.
These quasars are big generators.
They convert gravitational energy into magnetic energy, and that magnetic energy gets converted into kinetic energy in the launching of these jets.
They carry so much energy, they can be detected clear across the universe.
Quasars continue to confuse astronomers.
Now, they're presenting us with another problem.
Quasars should take millions of years to fire up.
But recently, we've detected one that switched on in a cosmic heartbeat.
So far, we've discovered over 200,000 quasars.
And in June of 2016, we discovered another.
But this one is different.
It ignited in just 500 days In cosmological terms, just a blink of an eye.
That's incredibly weird, because remember what we're talking about here.
We're talking about the consumption of galaxy-sized quantities of gas.
How could that be fast? That's a very rapid process.
Usually, when we think of astronomy, we think of astronomically long time scales where we don't get to see things happen in real time.
So when we see these incredible engines in our universe changing their complete nature by turning on over the course of a few months or a few years, that's a little bit frightening.
What triggers a quasar to ignite? Scientists now theorize the quasars switching on may be a natural part of a galaxy's life.
Galaxies are not fixed things.
They're constantly changing, evolving.
It's also true that suddenly we see these things switch on, and it's kind of mesmerizing to imagine the situation.
Within a year's time, a galaxy could go from being normal to being active.
It's thought that most, if not all, galaxies go through a phase of development that includes forming a quasar, that it's a normal part of a galaxy growing up.
Quasars can act a lot like a teenager, tantrums and all.
This was when they were shining brightly, eating mass at an incredible rate.
It's almost like your teenage years, you know? You ate everything in sight, and things were pretty messy.
You might have undergone a lot of mood swings.
It's kind of like that with a quasar.
When a quasar gets hungry and raids the refrigerator, it can switch on.
So what flips the switch? What turns a quasar on and off? It fundamentally has to do with gas getting into the centers of galaxies.
When stuff gets in there, a black hole is waiting, and then it gets bright.
So where does a quasar find enough gas to feast on? To turn on a quasar, you need certain conditions.
You need a supermassive black hole, and you need a lot of material dumped on it.
What does this? A galaxy collision.
Galaxies are not locked in place.
They move through space.
Sometimes, they collide.
We think that the supermassive black holes, at their cores, will collide and merge, and the gas supply from the combined galaxies streams towards the new supermassive black hole.
It's almost like, when you have these two galaxies merging, that they have all new food.
It's a brand-new dinner plate, a brand-new buffet of food to eat.
Well, that's a feeding source, right? You're going to start a feeding frenzy on the black hole that's sitting there.
The gas spirals in, heats up to millions of degrees.
The galactic core lights up.
And a quasar is born.
It seems galaxy mergers provide the best conditions for quasar formation, but when astronomers studied the rapid ignition of these unusual quasars, they didn't find evidence of a galaxy merger.
Something else must switch them on.
When we think about the size scales of a typical quasar, we think it must take years to really turn on.
And if you're thinking about a flow of gas passing through the central parts of a galaxy to encounter the black hole, to activate the dynamo, to launch a jet, this should take a healthy amount of time.
This this is big stuff.
So what could speed this up? One idea is that something catastrophic happens inside the accretion disk, the ring of gas surrounding the black hole.
An active quasar means that a black hole is eating something, so when you see a quasar turn on, you know that something went very wrong around the black hole.
Maybe some of the disk fell in.
Maybe even a star got a bit too close.
Accretion disks are not just gas and dust.
Black holes will drag in anything and everything.
There are stars.
There's gas.
There's gas clouds.
There's stars in formation.
There are stars dying.
A lot is happening there, but basically, what happens is that star veers too close, and it is basically stripped.
It's pulled apart.
The enormous gravity of the black hole could tear a star to pieces, giving rise to a sudden surge of energy within the accretion disk.
Or perhaps, an exploding star could be the catalyst for quasar ignition.
So it could be that a supernova going off in the accretion disk triggers an avalanche of material suddenly being able to fall in on the black hole.
In both cases, a sudden rush of hot gas would heat up the accretion disk, switching on the quasar.
You need to do something violent to a galaxy to let it really feed enough to create a quasar activity.
Once activated, a quasar can shine for millions of years, blasting out energy and destructive jets.
We see them across the universe.
It seems the basic ingredients are quite common, even in our own neighborhood.
Let's put all this together.
What do you need for a quasar? You need a galaxy.
You need a central supermassive black hole.
You need gas, and you need stuff falling into that black hole to create the quasar phenomenon.
Well, we live in a galaxy, the milky way, and it has a central supermassive black hole, and there's gas orbiting around near there.
That doesn't sound good.
Jets ripping through the milky way, heat and cosmic winds bursting out from the core, posing the question Would we survive? We're used to thinking of our galaxy as peaceful.
But what if it isn't? What if it's hiding a violent past? What's been discovered recently is kind of fascinating.
There's two large evacuated bubbles emanating from the center of our galaxy.
The bubbles are full of superheated gas, and they're moving out of our galaxy at 2 million miles per hour.
These bubbles are huge.
They're on the scale of the galaxy itself.
They're 50,000 light-years long.
They're so big that if you were to map them out on the sky, they would stretch from horizon to horizon.
These gas bubbles look similar to those seen within distant galaxy clusters like hydra a.
One big question is, what could've put that gas there? What could have made this gas so hot that it's able to puff out so far from the galaxy? One possibility is that this was driven by an active phase in our galaxy's history.
Far away, in the heart of our galaxy, hidden by gas and clouds, lies a giant A supermassive black hole called Sagittarius a-star.
Now, it's quiet.
Is it dead or just sleeping? The only thing that could have created these vast lobes of material above and below the milky way are giant jets streaming out of the core of our galaxy.
Well, doesn't that sound a lot like a quasar? But unlike hydra a, the expelled gas doesn't date from hundreds of millions of years ago.
These were blown out within the last 6 million years.
Almost all quasars we see are in the distant universe, which means they're in the distant past.
But here we have recent activity.
Just 6 million years ago, our central black hole was feeding.
No one really expected that because, for as long as we can remember, we've thought about our milky way galaxy as being quiescent, that is to say not really eating too much, sort of like a black hole on a diet.
Something must have broken its diet.
Maybe an unfortunate group of stars strayed too close.
Whatever the delivery method, the sleeping Sagittarius a-star gorged on its new meal and woke up explosively.
Its jets blasted over a trillion trillion trillion tons of gas out of the galaxy.
Thankfully, our black hole is much smaller than a typical quasar.
This was only a small outburst, but it's possible our sleeping giant could wake up again, much bigger and much more dangerous than ever before.
There's something coming up that means that one day, you may walk outside, look at the night sky and realize the quasar has turned on.
We know quasars can be triggered by galactic collisions, and we know a galaxy is heading our way.
Public safety announcement The milky way galaxy is on a collision course with Andromeda.
It's traveling at us at about 70 miles a second, and in about 4 billion years, these two galaxies are going to collide.
Both of us have supermassive black holes.
Ours is 4 or 5 million times the mass of the sun.
And Andromeda's black hole is 20 times larger.
Eventually, those black holes will start spiraling around each other, and they're destined to merge.
The new black hole will be much bigger than Sagittarius a-star, and this supergiant will have a fresh load of gas to consume.
This will be an incredible explosion for the milky way, maybe even the biggest explosion it's ever had in its whole life cycle.
A quasar could be born far bigger than anything we have experienced before.
In the chaos of the merger, our solar system could migrate, moving closer to the galaxy's core, closer to the quasar.
We will have a front-row seat to not only colliding galaxies, but in fact, something even more amazing and terrifying, a quasar being switched on.
The closer we are, the bigger the spectacle.
It would look like a single bright source in the sky, almost like a second sun.
Along with the beauty will be incredible heat, quasar winds, and, perhaps, even jets.
What will all this mean for Earth? The atmosphere is going to be stripped away.
Oceans are going to boil.
Maybe the rock under your feet will melt.
I mean, we're talking about a tremendous amount of energy here.
There would absolutely be no life on Earth.
The newly ignited quasar may be so energetic it blasts trillions of tons of gas out of the milky way.
Even the basic ingredients for future stars and planets could be at risk.
That's where stars form, and that's where planets form, and so if you kick all the normal matter out of the galaxies, you no longer get stars and planets and humans and civilizations.
That doesn't sound like such a good idea to me.
With their terrible destructive force, quasars seem like bad news for galaxies.
But we are now discovering there's another side to them.
Quasars are putting out so much energy, they appear to be so disruptive to their environment, but it could be that, without them, we wouldn't be here.
For all their ferocious power, quasars might be the ultimate cosmic creators.
Kicking out unimaginable power, quasars can cause chaos in their local environment, but it's possible that this might be essential for a healthy galaxy.
It might even create the conditions for life.
We're discovering that for all their destructive properties, quasars also have a creative side, so it very well may be that the universe we see around us was shaped by quasars.
Stars are the essence of a galaxy, but everything in moderation.
Too many stars can actually be a problem.
Having a lot of new star formation is kind of a good thing, but too much of it can be a bad thing.
When new stars are born, many of them are going to be hot, large, blue stars, but eventually, those young, hot stars are going to start to die, and when they do, they're going to explode violently as supernovae.
There will be new black holes.
There will be jets.
There will be shocks that actually go through the gas of the galaxy.
All of that is, effectively, killing the galaxy.
Large bursts of star formation make the galaxy violent and chaotic.
Stars and planets are wiped out by intense radiation from supernovas and black holes.
Left unchecked, the galaxy burns itself out.
But some galaxies have a cosmic guardian creating quiet, peaceful neighborhoods.
Something is controlling star birth.
In order for stars to form, you need cool gas, molecular hydrogen, and a quasar is anything but cool.
They're cool to think about, but they're really hot if you're near one.
If you're a galaxy, and you're ready to just form a bunch of stars, but then a quasar turns on in your heart, that's going to impact how those stars form.
So the fate of cold gas in a galaxy is incredibly tightly coupled to the fate of star formation throughout that galaxy, and we think that quasars deposit so much energy into their ambient surroundings that they can prevent the formation of very, very cold gas by heating it up.
Quasars pump huge amounts of heat into their environment.
One way they do this is through an extreme cosmic hurricane called a quasar wind.
You have a wind of light.
There's just so much light that's being powered by this spinning disk of material around this supermassive black hole that that light can actually push on the dust and the gas in the core of the galaxy and push it outwards very rapidly, and these winds can be really fast.
It's not the kind of wind you and I are used to thinking about.
It's actually a stream of high-energy particles.
In some cases, these particles can be traveling at hundreds of millions of miles an hour.
The cool, star-forming material in the galaxy becomes hot and turbulent.
Instead of having these nice, tranquil clouds of molecular hydrogen collapsing under gravity, now here comes this big, giant nasty quasar wind disrupting everything.
It's going to basically warm the galaxy too much, and that galaxy is going to have what we call quenched star formation, so it's going to have a lower rate of forming new stars than we would expect it to.
Quasars have another star-suppressing weapon in their cosmic armory.
There's another mode that we think exists, and that is mechanical, or kinetic, feedback, and that is literally this.
Right? That is momentum injection.
That is a freight train plowing through a galaxy in the form of a jet launched by the supermassive black hole, and that jet, just like a truck plowing a snowy street, pushes material out of the way.
They bulldoze the gas to the outskirts of the galaxy.
They blow out tremendous amounts of energy.
They spit out gas, and what happens is it stops the process of star formation.
There's less fuel for new stars to be made.
Quasars suppress star formation with winds and jets.
But if they continue ejecting gas, they would permanently shut off star birth, killing their galaxy.
Luckily, they stop before causing fatal damage.
Eventually, the gas in the center of that galaxy is going to run out, and when it does, it's like a light switch, and you're turning the quasar off.
Quasars are fueled by cool gas.
Having blown away its fuel, the quasar itself will die.
Gas clouds cool, and stars begin to form again.
But the cooling gas also falls back towards the supermassive black hole, providing new fuel for the quasar to reignite.
And so the black hole, in a lot of ways, can shut itself off, just like a thermostat in your living room, where, if the room gets too cold, your thermostat kicks in.
The heat turns on and gets to a point where the room is now too hot, and the thermostat kicks off.
When the quasar turns on, it's like you stop star formation, and then when it turns off, it's like you've turned star formation back on.
Quasars regulate star formation so that not too many stars are formed all at the same time.
By regulating star formation, quasars control the future star formation of the galaxy.
So we think as quasars as these incredibly violent phenomenon, but in actuality, they are much more subtle and elegant than you might think.
In a sense, they're a force for creation, as well, because they are mitigating how stars are forming in galaxies.
It's very likely that quasar activity is essential for galaxy development, so in that sense, we have an equilibrium generated by quasar activity.
You could keep them on an even keel.
Quasars are a rite of passage for young galaxies, graduating from chaotic star-forming adolescence into mature, stable galaxies like our own.
The existence of quasars may be essential to the health of a galaxy.
But we think they play an incredibly important role in the evolution of galaxies throughout cosmic time.
Quasars are the most energetic objects in the universe.
They seem to almost defy the laws of nature, but they're also tools.
They're tools that allow us to understand our own origins.
We can use quasars to help understand the origins of galaxies, the origins of stars.
Quasars help create stable galaxies, the kind of galaxies that could sustain life.
We are connected to the universe in a beautiful and fundamental way.
So quasars, even though they're incredibly violent, they're a part of galaxies, and they're a part of galactic evolution.
Sometimes, in order to create, you have to destroy.
Quasars have shaped the universe.
Without them, we might not even exist.