How the Universe Works - S09E01 - Journey to a Black Hole
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00:00:00We're on a journey to the heart of the supermassive black hole, M87 Star.
00:00:09Our mission?
00:00:10To investigate one of the most mysterious places in the universe.
00:00:15M87 is a great target for us to visit because one, it's close, and two, it's active.
00:00:24It's feeding.
00:00:27Supermassive black holes are the engines that power the universe.
00:00:32Supermassive black holes are a key factor in the birth, life, and eventual death of
00:00:38galaxies.
00:00:39And the more we study them, the more puzzling they become.
00:00:45They're the master key to most of the unsolved mysteries in physics.
00:00:50The physics inside a supermassive black hole are beyond weird.
00:00:55They are the final frontier of our understanding.
00:01:00Your imagination can run wild.
00:01:01Maybe it's even the source of other universes.
00:01:04There's only one way to find out.
00:01:07To go where no one has gone before and journey to the heart of M87 Star.
00:01:25We speed across M87, a gigantic galaxy 55 million light years from Earth.
00:01:41At its heart lies a supermassive black hole, M87 Star.
00:01:50It is the first and only black hole ever photographed.
00:01:55We want to find out how M87 Star grew so large, what lies inside, and how it controls
00:02:03the galaxy.
00:02:08Five thousand light years out from the supermassive black hole, we get our first sign of the danger
00:02:15ahead.
00:02:16We see giant holes carved out of the galaxy.
00:02:21Starless voids, thousands of light years wide.
00:02:26As we approach, we can see that wreckage littered around the vicinity.
00:02:32It's like entering the lair of the dragon and seeing the bones of all the explorers
00:02:36who came before you.
00:02:40What cataclysmic force tore these giant cavities and the galactic gas clouds?
00:02:48As we fly next to a brilliant shaft of energy, thousands of light years from M87 Star, we
00:02:58get a clue.
00:03:03It's a deadly stream of radiation shooting out across the galaxy, a jet.
00:03:10This jet looks like a searchlight or a beam from a lighthouse.
00:03:17You're seeing this monumental thing screaming out of the black hole, blasting out radiation.
00:03:24When I first saw a photo of a jet, I was like, whoa, am I misreading the scale of this image?
00:03:31Because there was this crazy Star Trek-like beam that's coming out.
00:03:38In 1918, American astronomer Heber Curtis described the jets as a curious straight ray.
00:03:48A century later, observatory images reveal they pulsate with energy.
00:03:55The images show knots and clumps in these jets.
00:04:00They show that it's just not smooth and nice, that there's been a history of violence inside
00:04:06this jet.
00:04:10This violent energy pushes the knots along the beams.
00:04:15The knots reveal the speed of the jets.
00:04:21It's like looking at a fast-moving train.
00:04:25Rail cars of the same color blur into one continuous image.
00:04:33Different colored cars stand out against the others.
00:04:38It's the same with the knots moving along the jets.
00:04:43So we can figure out how fast the jets are really moving by looking at knots of material
00:04:48coming out from near the black hole.
00:04:51When astronomers measured the speed of two knots, they got a big surprise.
00:04:57One is moving at 2.4 times the speed of light, and the other is moving over six times faster
00:05:03than light.
00:05:04How could this possibly be?
00:05:08As weird as the physics around a black hole is, that's not actually happening, nor is
00:05:12it allowed to happen.
00:05:14Nothing can actually go faster than the speed of light, so obviously we're missing something
00:05:19here.
00:05:21The knots may seem to break the speed of light, but the universe is just playing with us.
00:05:29It's really just a consequence of the fact that a lot of this jet is pointed toward us,
00:05:35pointed partially toward the observer on Earth.
00:05:39That in a sense is sort of optical illusion tricks you into thinking it's moving faster.
00:05:45It's a simple trick of the light, a bit like the way a spoon in a glass of water looks
00:05:51bent and distorted.
00:05:53The impossibly fast speed of the jet is just an illusion of perspective.
00:05:59From our perspective, it looks like the whole thing is moving towards us faster than light,
00:06:04but really it's just cruising along very, very fast.
00:06:09The jets aren't actually breaking the laws of physics.
00:06:11They're pushing up against it.
00:06:12They're going at 99.9999995% the speed of light.
00:06:18Imagine the energies necessary to accelerate this entire jet to that speed.
00:06:26So what could produce enough energy to blast jets across the galaxy at close to the speed
00:06:32of light?
00:06:35There is a clue far ahead.
00:06:38The jets shoot out from a tiny, brightly glowing object.
00:06:44This is where things go nuts.
00:06:46This is the center of the action.
00:06:48This is where the real stuff happens.
00:06:51A ring of super hot gas and dust whirls around the supermassive black hole.
00:06:59It's called the accretion disk, and it shines a billion times brighter than the sun.
00:07:08If you had a ringside seat next to M87 Star, you would probably be fried very, very fast.
00:07:21But if you were some, you know, magical being and could survive anything, and if you had,
00:07:25you know, a million SPF sunscreen and really, really great sunglasses, what you would see
00:07:29is this enormously bright vortex of gas swirling this dark void.
00:07:37This bright vortex spins around the supermassive black hole at over 2 million miles an hour.
00:07:45So there's a tremendous amount of friction as material moving slower and faster rubs
00:07:49against each other.
00:07:50That's what's heating the disk up, and that's what's causing it to glow.
00:07:56Temperatures reach billions of degrees, making this one of the hottest and most electrically
00:08:01charged environments in the whole universe.
00:08:06This intense energy lights up not just the disk, but also illuminates our path across the galaxy.
00:08:15So these supermassive black holes are some of the brightest objects in the known universe.
00:08:20They can outshine the light of all the stars in an entire galaxy by a factor of a thousand or more.
00:08:30Such intense light clusters were first detected when we started to explore space with radio
00:08:35telescopes in the 1960s.
00:08:49Centuries ago, astronomers began to see these incredibly bright sources in the deep sky.
00:08:56And they knew they were far away, and they knew they were bright.
00:08:59It made them the brightest things in the universe.
00:09:02And astronomers had no idea what they were.
00:09:07It wasn't until years and years later that we found that these bright sources were powered
00:09:13by giant black holes.
00:09:19Scientists think that the intense energy of the accretion disk is the source of the jets.
00:09:25The hot swirling gas and dust produces powerful magnetic fields.
00:09:31As the disk spins, it twists up the magnetic fields at the poles of the black hole.
00:09:37Energy builds.
00:09:39Finally, the magnetic fields can't contain the energy any longer.
00:09:45They snap and blast the jets out into the galaxy.
00:09:50Even many light years away on the ship, we can see this violent release of energy.
00:09:57It's like the universe's biggest fireworks display.
00:10:02Two jets streaking out of M87 star's poles.
00:10:07One shooting away into the distance.
00:10:11The other racing past our ship.
00:10:15We're at a safe distance.
00:10:17Other things are not.
00:10:20So when these jets shoot outward from this supermassive black hole, they don't shoot
00:10:24outward into nothing.
00:10:25If a jet hits a gas cloud, it annihilates it.
00:10:29It just punches a hole right through it.
00:10:32It's like a train going down a snowy track, right?
00:10:35The gas is like the snow, and the jets are like this freight train plowing across it.
00:10:42But here, a freight train traveling at close to the speed of light.
00:10:49Smashing into clouds of gas.
00:10:55Lighting our way to M87 star as we follow the trail of destruction.
00:11:05There is evidence of similar destruction across the universe.
00:11:11In the Cygnus A galaxy, supermassive black hole jets have caused damage on a colossal
00:11:17scale.
00:11:20In many ways, Cygnus A is like a cosmic shooting gallery.
00:11:23You see this crime scene, this beautiful mess.
00:11:26So when this jet comes out of the nucleus of Cygnus A, it's going to encounter gas clouds.
00:11:33At that point, shockwaves set up.
00:11:35And this jet just rips right through this material, sending shockwaves in every direction,
00:11:40creating absolute chaos.
00:11:43It's hard to believe how much devastation these jets can cause.
00:11:48They're punching a hole in the gas 100,000 light years wide.
00:11:51I mean, that's the scale of an entire galaxy.
00:11:56In 2020, more carnage was discovered in a galaxy 390 million light years away.
00:12:06The Ophiuchus galaxy cluster is a collection of a huge number of galaxies all orbiting
00:12:10each other, held together by their own gravity.
00:12:13And when astronomers looked at it, they saw something they didn't understand.
00:12:16It looked like a wall of gas there.
00:12:19At first, we didn't know the cause.
00:12:22Turns out, we know it was a powerful jet hitting a huge cloud of gas.
00:12:31The supermassive black hole in the galaxy in the center of this cluster is blasting
00:12:35out material that has carved a cavity well over a million light years across.
00:12:41This is a vast hole in the gas.
00:12:49Shockwaves from the jet hit the gas, triggering a monstrous explosion, which carved out a
00:12:55cosmic void 15 times the size of the Milky Way.
00:13:00The wind from this black hole has swept up that material like a snowplow pushing snow.
00:13:06That's what's causing that wall that the astronomers saw.
00:13:09And the amount of energy this takes is huge.
00:13:12It's 800 billion billion times the sun's energy that it will emit over its entire 12
00:13:20billion year lifetime.
00:13:26As we head towards the center of the M87 galaxy, we enter hostile territory.
00:13:33The closer to the supermassive black hole we travel, the more dangerous it gets.
00:13:40As we approach the central core of M87, we start to feel it.
00:13:45All this energy, all this ferociousness is powered by that black hole.
00:13:51Intense winds start to buffet the ship.
00:13:57They push away vital gas, quenching star birth.
00:14:04Could these winds end up killing the galaxy and M87 star itself?
00:14:19We're on a mission to explore the supermassive black hole M87 star.
00:14:27First, we have to cross the M87 galaxy.
00:14:32It's 120,000 light years across, and it looks like a giant puff ball.
00:14:39M87 is an absolute monster.
00:14:42It's a giant elliptical galaxy, and that means that as you go from the edges to the interior,
00:14:48you see a higher and higher density of stars.
00:14:52This vast galaxy contains several trillion stars.
00:14:57What's strange is that almost all of them are the same color.
00:15:04So as you see, your sky is covered with countless red points of light everywhere you look.
00:15:14Most of these points of light are small, long-living stars called red dwarfs.
00:15:21So what happened to the different colored stars that we see in other galaxies?
00:15:27When you create lots of stars, you make lots of blue and red stars, but the blue ones don't
00:15:31last very long.
00:15:32They explode and are gone.
00:15:34The red ones, the ones that are lower mass, those are the ones that live for many, many
00:15:38billions of years.
00:15:39M87 hasn't made stars in so long that its stars are mostly red.
00:15:45We call galaxies with mainly red stars red and dead.
00:15:51So the only stars that are left in these red and dead galaxies are billions of year old
00:15:57populations.
00:15:58And since it's not making new stars, the clock is ticking on M87.
00:16:04Essentially it's a dead galaxy walking.
00:16:08The M87 galaxy hasn't made any new stars for billions of years.
00:16:15Something had to make that happen.
00:16:17Something had to deplete or heat up or push away the gas in those galaxies that would
00:16:23otherwise go into forming stars.
00:16:25We think that black holes in the centers of galaxies are the ultimate answer to this.
00:16:32So how did M87's star kill off star formation billions of years ago?
00:16:39As we cruise towards the supermassive black hole, we get a clue from the strong winds
00:16:45buffeting the ship.
00:16:48So these winds can be incredibly powerful and really, really fast, right?
00:16:53If you think a hurricane on Earth is bad, you should see some of these winds.
00:16:58Space wind is very different from wind on Earth.
00:17:04Earth winds are moving air.
00:17:08When the sun heats a surface on our planet, the air above warms and rises.
00:17:18The cool air below fills the space left by the rising warm air, creating winds.
00:17:28In space, winds are made up of gas and superheated plasma.
00:17:33The power that generates the winds lies ahead.
00:17:37The bright accretion disk surrounding M87's star.
00:17:42Because it's so incredibly hot, it liberates an enormous amount of light.
00:17:46And that light can drive a wind.
00:17:49And so black holes can power winds.
00:17:52They power winds with light itself.
00:17:56And the more material that's falling into that accretion disk, the bigger and hotter
00:18:00it gets, and the more powerful the wind is that the black hole blows.
00:18:04We understand that light from the accretion disk creates the winds, but that is about
00:18:10all we know.
00:18:12We don't know that much about the wind.
00:18:14Is it expanding in all directions, like a sphere?
00:18:17Or is it aimed in jets, very narrow and only moving in two different directions?
00:18:22Now measuring the effect of the winds isn't as easy as you might think.
00:18:25It's not like going outside on a windy day and doing one of these.
00:18:29You have to infer what's going on with the winds by studying the light emanating from
00:18:33this object.
00:18:36We wanted to find out if black hole winds expand like a bubble or travel in narrow streams.
00:18:43So we studied how iron dust from the accretion disk blocks the light driving the wind.
00:18:52Astronomers found the answer when they looked in the X-ray light spectrum.
00:18:58And what they detected was iron absorbing those X-rays in every direction they looked
00:19:03around the black hole.
00:19:04That's only possible if the black hole is blowing out a wind in every direction, which
00:19:09means that it is definitely blowing out a spherical wind which is expanding into that
00:19:14galaxy.
00:19:15And so these black holes can almost literally inflate this growing sphere or bubble of gas
00:19:20that's outward flowing from the heart of the galaxy.
00:19:25These winds push out throughout the entire galaxy of M87, transporting heat and energy
00:19:34throughout the entire volume of the galaxy.
00:19:38What we found is that it's expanding away from the black hole at a quarter of the speed
00:19:43of light, 40,000 miles per second.
00:19:48And for the M87 galaxy, that is bad news, because hot powerful winds kill off star birth.
00:19:58The winds can push away the gas that would have normally formed stars.
00:20:04So they can effectively quench star formation in a galaxy, causing it to gradually die.
00:20:13And it gets worse.
00:20:15In order for a galaxy to produce stars, it needs lots of gas and dust, and that gas and
00:20:20dust needs to be incredibly cold.
00:20:24Hot winds from the black hole heat up gas clouds so they can't collapse into stars.
00:20:31As M87's star has grown, it has slowly shut down star formation.
00:20:38As the black hole in the center of the galaxy grows, it has stronger and stronger winds.
00:20:42And this means it's going to drive out more and more matter.
00:20:46And that's what makes it a galaxy that can no longer support star formation.
00:20:51So a supermassive black hole can determine the star formation happening in the galaxy.
00:20:56It can help to regulate the amount of gas in the galaxy, and therefore the number of
00:21:01stars that are formed in a galaxy.
00:21:05Although M87's star is tiny compared to the vast galaxy around it, it still controls its host.
00:21:15When you compare it to the size of the galaxy it's sitting in, it's like comparing a grape
00:21:20to the size of the Earth.
00:21:22So to think that something so relatively small compared to the galaxy could have such a profound
00:21:27effect over effectively all of cosmic history is just this remarkable illustration of how
00:21:33energetic a black hole can be.
00:21:36In the relationship between a supermassive black hole and the material surrounding it,
00:21:41the black hole is in charge.
00:21:47But not all supermassive black holes kill off star formation.
00:21:54The Phoenix Cluster contains a supermassive black hole, but produces enough cold gas to
00:22:01form 500 stars a year.
00:22:06This is a place where we'd normally expect to only see hot gas.
00:22:09Here's the mystery.
00:22:10Why is all of this cold gas so far out in the galaxy?
00:22:15Observations reveal that jets shooting out of the supermassive black hole inflate giant
00:22:22gas bubbles 82,000 light years through the galaxy.
00:22:29When the team superimpose a map of the cold gas over a map of the hot bubbles, they line up.
00:22:36There's something about those hot bubbles that are allowing this cold gas to be created
00:22:40kind of drooped on top of it.
00:22:43When the jets move out and inflate the bubbles, they drag behind a wake of slightly cooler gas.
00:22:51This colder gas starts to form more stars.
00:22:56So the black hole can redistribute gas, and it can heat up gas, and it can also cool down gas.
00:23:01And so that way it can regulate the environment inside of the galaxy.
00:23:14Although M87's star calls the shots, its past, present, and future are inextricably linked to its host galaxy.
00:23:26The view from our ship is endless space, calm and unchanging.
00:23:34But the M87 galaxy has a violent past.
00:23:39A history of cannibalism, death, and destruction.
00:23:51We've traveled thousands of light years across the M87 galaxy,
00:23:56but its supermassive black hole is still far in the distance.
00:24:02From our current position, M87's star may look small, but it's 6.5 billion times the mass of the sun.
00:24:12So how did it get so big?
00:24:15One of the big mysteries that we're still trying to understand is
00:24:19what controls how big the giant black holes at the centers of galaxies become.
00:24:24And we know that it's tightly correlated with things like how big the galaxy is.
00:24:29Bigger galaxies have bigger black holes.
00:24:33To understand how M87's star became so big, we have to investigate the history of its galaxy.
00:24:40We need to discover how M87's star's host galaxy grew so large.
00:24:47M87 is huge. It's a big galaxy with a big black hole.
00:24:54It's really, really big. It's what we call a brightest cluster galaxy.
00:24:58And these so-called brightest cluster galaxies are among the most massive galaxies in the known universe.
00:25:04Usually, a galaxy with the mass of M87 is much smaller.
00:25:09But M87 is puffed up hugely. Why?
00:25:14One lead comes from the layout of M87's stars.
00:25:19As we travel through the galaxy, we see that the stars spread out over an area 100 times larger than expected.
00:25:27So, what scattered the stars?
00:25:31Galaxies aren't static. Every galaxy is moving.
00:25:35And sometimes galaxies get very close and can interact with each other.
00:25:40Interact is a polite way of describing something extremely brutal.
00:25:47Galaxies are colliding with other galaxies. They're cannibalizing smaller galaxies or tearing each other apart.
00:25:55Sometimes they're like drive-bys and they'll warp each other's structures.
00:26:00Sometimes the galaxies have head-on collisions and merge.
00:26:05Merging pulls in new gas and stars.
00:26:10So galaxies grow larger.
00:26:15Galactic cannibalism is common.
00:26:21Maybe the M87 galaxy ate its neighbors.
00:26:27But how can we find out?
00:26:30We could try to identify stars that came from the consumed galaxies.
00:26:36But that's not straightforward.
00:26:39When you're trying to map out a distant galaxy, it turns out using their stars is a really hard thing to do.
00:26:44They smear in with the foreground and the background.
00:26:47It's actually very difficult to see any evidence that that galaxy merger ever happened.
00:26:51It's all smoothed out. It's kind of like throwing a bucket of water into a pond.
00:26:55And then asking after the waves go away to separate which molecules of water came from the pail of water versus which were in the pond.
00:27:03All you see is just a mixed pile of water.
00:27:06And it's similar to that with the stars in a galaxy.
00:27:11So how can you spot water from the bucket in the pond water?
00:27:17We need to detect signs of disruption, like ripples or distinct streaks of sand and mud thrown up by the disturbance.
00:27:28When galaxies merge, they may also leave a leftover that stands out, like a planetary nebula.
00:27:36Planetary nebulae are these bright beacons that you can pick out and map out the galaxy with great precision.
00:27:43A planetary nebula forms when a dying, mid-sized star blows off its outer layers after running out of fuel.
00:27:52These outer layers of gas expand, forming a nebula, often in the shape of a ring or bubble.
00:28:00And you see this beautiful, glowing, blue-green blob coming away from the star.
00:28:04These are so much bigger than stars, you can pick them out very easily.
00:28:09One team went planetary nebula hunting in the M87 galaxy.
00:28:14As they mapped the galaxy, they picked out 300 distinct, glowing points.
00:28:21The points are blue-green, confirming they're planetary nebulas.
00:28:28Planetary nebulae are great.
00:28:30They really stand out like needles in a planetary haystack.
00:28:34The nebula's movements are distinct from the stars in M87.
00:28:39This shows they formed in a smaller, younger galaxy, not M87.
00:28:45Because we see these planetary nebulae, something must have happened in this old, dead galaxy.
00:28:50What was it? A galaxy collision.
00:28:54The discovery of the planetary nebulas shows that at some point in the last billion years, M87 ate a smaller galaxy.
00:29:06This galaxy strayed too close to the much larger M87.
00:29:13M87's powerful gravity snared the smaller galaxy and dragged it closer and closer.
00:29:22You could actually see this galaxy getting bigger and bigger and bigger in the sky.
00:29:26And it wouldn't stay the same shape.
00:29:28As the galaxy got closer, it would begin to distort.
00:29:31And your galaxy would distort as well, until the sky was filled with rivers of stars.
00:29:40M87 pulled in the small galaxy and swallowed it whole.
00:29:48Can you think of anything more dramatic than the collision of two galaxies?
00:29:52A violent history of mergers explains how the M87 galaxy grew so large.
00:30:00Each event brought in many millions of stars.
00:30:05The collisions also unleashed enormous gravitational forces, scattering the stars like confetti.
00:30:16After a collision like this, the stars are probably 10 to 100 times more spread out than they were before.
00:30:24Some collisions threw stars around.
00:30:27Others changed the shape of the entire galaxy.
00:30:32If that galaxy merger is violent enough, it injects so much energy into the galaxy that the stars basically all move away from the center.
00:30:41And it makes the galaxy much more puffy.
00:30:44Eventually transforming it into the smooth, featureless elliptical shape.
00:30:53Most galaxies have a supermassive black hole at their center, including those galaxies eaten by M87.
00:31:01So what happened to those black holes?
00:31:04Did they merge with M87 star, increasing its size?
00:31:09M87, the fact that it's an elliptical galaxy, also supports the fact that it's had multiple supermassive black hole mergers,
00:31:16which is how M87 star could have gained its sizable mass.
00:31:22Compared to its violent history, the M87 galaxy is now relatively calm.
00:31:28We think that in the past, M87 star grew by gobbling up other supermassive black holes brought in by collisions with other galaxies.
00:31:42But we don't really know, because physics suggests that supermassive black holes can never merge.
00:31:51Instead, they lock together in a cosmic dance for eternity.
00:32:03As we travel closer to the supermassive black hole, we pass the remnants of smaller galaxies eaten over the last 10 billion years.
00:32:13They reveal how the M87 galaxy got so vast.
00:32:19Most of these consumed galaxies probably had a supermassive black hole of their own.
00:32:27If M87 got so large by eating galaxies, did M87 star get supermassive by consuming other supermassive black holes?
00:32:41So when galaxies merge, all their stars and nebulae mix together, and then also their supermassive black holes eventually find each other and find their way down to the center of the newly merged galaxy.
00:32:56Just like dropping two stones into a pond, they'll both reach the bottom, they'll both move toward the center, and they will start to move ever closer together.
00:33:06But do the supermassive black holes actually collide?
00:33:11We've witnessed the merging of smaller stellar mass black holes.
00:33:16And we've seen supermassive black holes get close together, but we've never observed the merge.
00:33:24When galaxies merge, their central supermassive black hole should merge.
00:33:29The first step in the merger process, they're sinking toward the center of this newly formed galaxy.
00:33:35As they plunge towards the galactic center, the supermassive black holes plow through fields of stars and clouds of gas.
00:33:45They don't just run into each other, they end spiral toward each other.
00:33:49So they're going to scatter stars everywhere, and the closer they get, the more rapidly they will orbit each other, so things get even more and more chaotic and crazy.
00:34:01In all the chaos, something strange happens.
00:34:05The supermassive black holes stop moving closer to each other.
00:34:11This is a problem, and we call this the final Parsec problem.
00:34:16So what's going on? Why do they stall?
00:34:20The final Parsec problem happens when two supermassive black holes run out of material to help them to merge.
00:34:28There's not enough stars or gas that the black holes can interact with.
00:34:32It takes longer than the age of the universe for them to lose enough energy to merge.
00:34:37And so the black holes effectively stall at this final Parsec of separation.
00:34:45The two supermassive black holes lock together in an eternal cosmic dance.
00:34:51Close, but forever apart.
00:34:55But some supermassive black holes must have merged.
00:35:00It's highly likely that many of the galaxies M87 swallowed had supermassive black holes.
00:35:08And yet, on our trip, we haven't seen lots of supermassive black holes, just one, M87 star.
00:35:19So, mergers take place, but how?
00:35:25In 2019, we got a clue from a galaxy called NGC 6240.
00:35:35This particular galaxy looks like the aftermath of a massive galactic collision.
00:35:42There are lumps and clumps of stars, random groups at random directions and random velocities.
00:35:48It's all mixed up, which is what we think galaxies look like after a massive merger.
00:35:55The merger aftermath reveals a more complex series of events than a two-galaxy collision.
00:36:02What we find in the center of this galaxy isn't two, but three giant black holes,
00:36:08which suggests that there have been three galaxies colliding in recent history.
00:36:17So when this new galaxy starts to merge with the galaxy that hosts the stalled pair,
00:36:22it brings in its own third supermassive black hole.
00:36:25Now this supermassive black hole perturbs the system and it makes what's at the center highly unstable.
00:36:32The gravity of this third supermassive black hole steals orbital energy from the stalled pair, pushing them closer together.
00:36:41It's almost a thief that comes in and takes away some of that rotational energy from this binary black hole system.
00:36:49As the two supermassive black holes lose orbital energy, they finally come together.
00:36:56The likeliest thing to happen is that the least massive supermassive black hole is ejected,
00:37:03and the remaining two merge very quickly.
00:37:07The high-speed merger will last just milliseconds, but it will trigger a gigantic explosion.
00:37:16When these giant black holes merge, more energy is released in this process than our entire galaxy will emit over the course of billions of years.
00:37:30Perhaps M87's star merged with other supermassive black holes in the same way,
00:37:36a third black hole helping it to overcome the final Parsic problem.
00:37:44It's possible that mergers with other supermassive black holes allowed M87 to reach its sizable mass of 6.5 billion solar masses.
00:37:55Supermassive black holes meet their match when they square off against each other.
00:38:02The fallout is cataclysmic, and as we get closer to M87's star, our mission becomes more dangerous.
00:38:11We enter the gravitational kill zone surrounding the supermassive black hole.
00:38:18We know the dangers. Any unwitting stars that get too close are stretched, shredded, and torn apart,
00:38:28creating one of the biggest and brightest light shows in the universe.
00:38:33But their death may solve one of the mysteries of supermassive black holes, how fast they spin.
00:38:43It's difficult to calculate just how fast a featureless black object hidden by a bright disk rotates.
00:38:51You need a lot of patience and a little bit of luck.
00:38:54Astronomy is sometimes a pretty opportunistic science.
00:38:57You have to be looking at the right place at the right time to figure out something new that we've never seen before.
00:39:04Recently, astronomers caught a break when they spotted an extremely bright flare in galaxy PGC 043234.
00:39:15It was hard to miss.
00:39:17The flare was 100 billion times brighter than the sun.
00:39:24And the energy output was absolutely ridiculous.
00:39:28If this happened in the center of our galaxy, it would have been so bright we could see it during the daytime.
00:39:37A routine search for a black hole in the Milky Way,
00:39:40it would have been so bright we could see it during the daytime.
00:39:46A routine search for supernovas, violent deaths of giant stars, detected the intense flash.
00:39:54ASSASSIN is this network of telescopes designed to look for brief high-energy events all around the sky,
00:40:02and primarily supernovae.
00:40:04They saw a bright flash, and they thought, oh, yay, another supernova.
00:40:11If you see a bright flash of light coming from a galaxy, that's kind of your first thought.
00:40:16But it didn't look like a supernova at all. It didn't act like a supernova flash would.
00:40:22It didn't have the right characteristics.
00:40:24It wasn't behaving like a typical supernova.
00:40:26It had to be something else.
00:40:29So they send out an alert to the astronomical community saying, hey, there's something cool happening in this region of space.
00:40:36Once an event is flagged as real, then what happens is other telescopes turn their attention to that event.
00:40:45The data revealed something strange.
00:40:49After the initial flash, there are still smaller flashes that repeat.
00:40:54And if you're going to kill a star in a supernova, there's nothing left to repeat like that.
00:41:01Intriguingly, it flashed on and off about once every 130 seconds.
00:41:08The flashes continued for 450 days.
00:41:13When astronomers looked at this galaxy in detail, they saw that this event happened right at the center.
00:41:18And there's a black hole there with about one million times the sun's mass.
00:41:22And that was, that's it, man, that's the smoking gun.
00:41:25What they observed was an extremely rare phenomenon, a tidal disruption event.
00:41:32Catching one live as it happens is an astronomer's dream.
00:41:37This was our first time catching a black hole in the act of feeding on a star.
00:41:43In galaxy PGC 043234, a star wandered too close to a supermassive black hole.
00:41:50As this unfortunate star got close to the black hole, the black hole is spinning.
00:41:56And the gravity around this monster black hole is so strong that it could pull the star apart.
00:42:07The side of the star closer to the black hole is feeling a much, much stronger gravitational pull toward the black hole
00:42:13than the far side of the star, because it's spinning.
00:42:16And what this does is it stretches the star.
00:42:21So it got ripped to shreds, it got shredded, it got pulled out and stretched and whipped around the black hole.
00:42:31And this stretches the star into some giant long arm and that swirls around and is trapped as it orbits the black hole.
00:42:38The accretion disk snares the shredded star.
00:42:43And what this means is that that accretion disk is going to increase its output of radiation, in particular, high energy radiation.
00:42:54As the star embeds in the accretion disk, a massive flare of radiation erupts, lighting up the universe.
00:43:01After this initial burst, the spinning star debris sends out a continuous stream of light.
00:43:11Our telescopes only pick up this radiation on each rotation of the disk.
00:43:17It's like seeing the beam from a lighthouse every five seconds.
00:43:22The flashes are the final pulses of a dying star.
00:43:27And those flashes reveal both the width and the rotation speed of the supermassive black hole.
00:43:36We learned that the central mass of the black hole is about one third of the mass of the star.
00:43:41Those flashes reveal both the width and the rotation speed of the supermassive black hole.
00:43:50We learned that the central mass of black hole is about 300 times wider than the Earth, but it's rotating every two minutes.
00:44:00It's rotating at half the speed of light.
00:44:03That's over 300 million miles an hour.
00:44:07We don't yet know how fast M87's star is spinning, but we do know the accretion disk rotates at over 2 million miles an hour.
00:44:17This glowing ring, hundreds of light years wide, now lies directly ahead of our ship.
00:44:25It is one of the most awe-inspiring and deadly places in the universe.
00:44:31And we are heading straight for it.
00:44:37M87's Star
00:44:43After our long trek across the galaxy, we finally face the mighty supermassive black hole at its center, M87's star.
00:44:53A dazzling glare confronts us.
00:44:56This is the accretion disk, a ring of hot gas and dust spinning at over 2 million miles an hour.
00:45:03M87's star's accretion disk is so bright, the Event Horizon Telescope photographed it from Earth, 55 million light years away.
00:45:15So I remember exactly where I was when that image was released.
00:45:18I was sitting with a bunch of my colleagues at the Center for Astrophysics, and we were all watching the press conference live and just absolutely slack-jawed when that image hit the screen.
00:45:26I was sitting in the airport when I saw this black hole image.
00:45:29About to take a flight to New York.
00:45:31I got so excited that I actually walked away from my backpack sitting there.
00:45:37Seeing that picture, it really doesn't leave room for doubt.
00:45:42Black holes are real.
00:45:45The Event Horizon Telescope photo is the first picture ever taken of a black hole.
00:45:52The image revealed M87's star.
00:45:56The image revealed M87's star spins in a clockwise direction, and it's 23.6 billion miles wide.
00:46:06That's around 3 million Earths lined up in a row.
00:46:10The photo also confirmed M87's star's membership in a very exclusive club.
00:46:17The 1% of supermassive black holes that actively feed.
00:46:22The image from the Event Horizon Telescope tells us that M87 is indeed actively growing and accreting and eating material around it.
00:46:30It shows gas swirling around that black hole on its way to being swallowed.
00:46:36But do all supermassive black holes consume material in the same way that M87's star does?
00:46:44Is it possible that different black holes have different table manners?
00:46:48Well, it turns out that's really true.
00:46:49Some are more delicate eaters.
00:46:51In 2018, we discovered a supermassive black hole 250 million light years from Earth that eats on a schedule.
00:47:03Now we have this case of a black hole that looks like it's feeding three times a day.
00:47:10It's having three square meals a day.
00:47:12Intense bursts of energy pulse out from M87's star.
00:47:16Intense bursts of energy pulse out from galaxy GSN 069.
00:47:23We see X-ray flares and bursts coming from the center of this galaxy, repeating every nine hours.
00:47:31And each burst is associated with a new feeding event.
00:47:37This supermassive black hole not only eats on a schedule, it has a very healthy appetite.
00:47:44Each one of these meals that this black hole is consuming is the equivalent of four of our moons in a single bite.
00:47:57So what exactly is this supermassive black hole consuming?
00:48:03The most likely contender is a star.
00:48:06We think that the star has been ripped apart and spread throughout an accretion disk.
00:48:13And then slowly over the course of hours, an instability builds up and some material falls in.
00:48:20When the infalling material from the star hit the supermassive black hole, it triggered a burst of X-rays.
00:48:30Then the system stabilized.
00:48:32Then the system stabilized.
00:48:35Until it sparked up again, creating a nine-hour cycle of bursts of energy.
00:48:44Then, in 2020, new observations spawned a different theory.
00:48:50The star wasn't caught on the accretion disk.
00:48:53The supermassive black hole had instead pulled it into orbit.
00:48:58Its orbit takes it near that black hole every nine hours.
00:49:03And every time it encounters the black hole, some of its material gets sipped off.
00:49:11Eventually, the GSN-069 supermassive black hole will lose its meal ticket.
00:49:19But it's luckier than many other supermassive black holes.
00:49:23Sometimes black holes just take a little nibble on the surrounding material and just give a little burp of radiation in response.
00:49:33A black hole burp generates strong shock waves that radiate out across the universe.
00:49:43We detected two of these energy outbursts in Galaxy J 1354 plus 1327.
00:49:51Located 800 million light years away.
00:49:56The huge burps suggested that the supermassive black hole at the core of this galaxy was snacking.
00:50:05It ate a bunch of material one time. That caused a burst of energy flowing outward.
00:50:10Then it feasted again and that caused another burp.
00:50:14What caused these separate outbursts?
00:50:17The belching black hole galaxy has a smaller companion galaxy.
00:50:24A gas stream links the two galaxies supplying an intermittent on-off food supply.
00:50:31There's actually a smaller satellite galaxy going around the bigger galaxy.
00:50:35The black hole in the middle is pulling streams of material off this little galaxy.
00:50:40Clumps of material from the companion galaxy move towards the black hole.
00:50:45Clumps of material from the companion galaxy move toward the center of J 1354.
00:50:51Once there, the supermassive black hole grabs them.
00:50:56Some gas streaming from the neighboring galaxy reaches the center of the bigger galaxy when the black hole feeds and then ejects a jet.
00:51:07When supermassive black holes like the one in J 1354 receive an irregular supply of food, a cycle is established.
00:51:17A routine that scientists call feast, burp, nap.
00:51:28The supermassive black hole we're headed towards, M87 star, doesn't do burp and nap.
00:51:34It feasts all the time.
00:51:38Stars come in and get ripped apart maybe once every 10,000 or 100,000 years, whereas M87 has been shining brightly for millions of years.
00:51:48It clearly has a supply of gas other than ripped apart stars that's feeding the accretion disk.
00:51:56This helps explain how M87 star grew to 6.5 billion solar masses.
00:52:05But what about the future?
00:52:09Will this supermassive black hole continue to feast?
00:52:14Or will it starve?
00:52:17To find out, we have to move even closer, across the accretion disk, to discover just how M87 star satisfies its insatiable appetite.
00:52:35Our ship passes over the accretion disk of M87 star.
00:52:42A blazing ring of gas and dust hundreds of light years across.
00:52:48This is the supermassive black hole's grocery store.
00:52:53Black holes are known for sucking in everything, but is that really true?
00:52:58Black holes don't really suck. It's a popular misconception.
00:53:01They don't just pull anything in.
00:53:04In fact, if the sun just instantly turned into a black hole today, the Earth would happily continue on in its orbit,
00:53:10because all that gravity cares about is how massive and how far away something is.
00:53:15Supermassive black holes like M87 star are a lot more massive than a regular sun-sized black hole.
00:53:23This means their gravity is greater and extends much farther out into the galaxy.
00:53:28Allowing supermassive black holes to attract dust, gas clouds, and stars from billions of miles away.
00:53:36But they don't gulp down everything they pull in.
00:53:41The way black holes eat matter isn't as straightforward as you might imagine.
00:53:46Earth gains mass every day from objects falling to it from space.
00:53:51So you might imagine that matter falling onto a black hole,
00:53:55is like meteorites falling onto Earth. They can come in from any direction and land anywhere.
00:54:02That's not the case around a supermassive black hole.
00:54:06The most efficient way for a black hole to consume matter is for it to grow an accretion disk.
00:54:14Accretion disks grow when gas and dust, dragged in by the supermassive black hole's gravity,
00:54:20spirals inward and piles up in a ring.
00:54:24The ring starts to spin from the combination of gravity and the momentum of the gas and dust.
00:54:31The spinning material flattens into a disk.
00:54:35The material doesn't fall straight in, it orbits its way in.
00:54:40And so it gets accelerated to incredibly fast speeds.
00:54:45Sometimes the matter ends up inside the disk,
00:54:47sometimes the matter ends up getting kicked away from the black hole.
00:54:51As we traveled through M87, we witnessed jets and winds from the supermassive black hole
00:54:58blast this material out into the galaxy.
00:55:02But there may be other things that stop food from entering a black hole.
00:55:09The black hole at the center of our Milky Way galaxy, what we call Sagittarius,
00:55:13The black hole at the center of our Milky Way galaxy, what we call Sagittarius A-star,
00:55:18appears to be swallowing material or eating at an incredibly low rate.
00:55:23To discover what's stopping Sagittarius A-star, or Sag A-star for short, from feeding,
00:55:30scientists studied infrared light moving out from the supermassive black hole.
00:55:36To do that, they needed to fly high in Earth's atmosphere.
00:55:40The problem is, water vapor in our atmosphere prevents the infrared light from space from getting down to the ground.
00:55:46SOFIA is an infrared telescope built into the side of an airplane.
00:55:52As bizarre as that is, it's a very stable platform.
00:55:56SOFIA can look at these objects emitting infrared in space and get really good observations of them.
00:56:03SOFIA focuses on the structure of the gas in the strong magnetic field
00:56:07at the center of the Milky Way.
00:56:12This high-resolution telescope can track the finest grains of dust.
00:56:17When all the dust grains in a cloud are aligned by a magnetic field,
00:56:22they scatter the light coming at them in a certain way, and we call this polarized light.
00:56:27The dust grains can actually map out the magnetic field embedded in that dust cloud.
00:56:31The telescope picked out the grains arranged in a spiral pattern
00:56:36and revealed the direction the grains were moving.
00:56:41This movement reveals why Sag A-star is starving.
00:56:46The magnetic field is channeling them into orbit around the black hole,
00:56:51instead of allowing them to fall in.
00:56:55So it's literally keeping those dust grains away from the black hole.
00:56:59The magnetic fields also pushed clouds of gas, Sag A-star's food source,
00:57:04away from the supermassive black hole.
00:57:09This is the situation now, but that's not necessarily the way things are always going to be.
00:57:14Because magnetic fields can switch directions.
00:57:19There's a lot of other junk out there, dust and gas and other stars,
00:57:24that as they get close, they can change the magnetic field,
00:57:27and that might allow that dust to fall into the black hole.
00:57:32Magnetic fields changing direction offers hope for Sag A-star.
00:57:39And magnetic fields could help M87 star feed.
00:57:46Our mission continues, following this material plunging down into the supermassive black hole.
00:57:58We set a course towards the event horizon,
00:58:03the boundary between the known and the unknown universe,
00:58:08where the laws of physics no longer apply.
00:58:16Our ship crosses the accretion disk.
00:58:21Ahead, the absolute darkness of the supermassive black hole, M87 star.
00:58:31According to black hole legend, this is where we meet our end, torn to shreds by gravity.
00:58:40We have so much wonderful imagery of what would happen if you were to fall into a black hole from science fiction.
00:58:46One idea that has caught popular attention is the notion that you get spaghettified when you fall into a black hole.
00:58:54This is me, this is a black hole, which is pulling stronger on my feet than on my head.
00:59:02And if this black hole is a little bit heavier than our sun,
00:59:07this difference in pull is so strong that I would actually get spaghettified, torn apart.
00:59:12So, will M87 star spaghettify us?
00:59:17The answer depends on the black hole's mass and volume ratio.
00:59:22A stellar mass black hole, with the mass of 14 suns, is just 26 miles across.
00:59:28That's about the size of Oklahoma City.
00:59:32Such an enormous mass and a small volume creates a very sharp image of the black hole.
00:59:37Such an enormous mass and a small volume creates a very sharp increase in gravitational tidal forces as you approach the black hole.
00:59:46With a small black hole, the strength of gravity changes so rapidly with distance
00:59:52that your feet could be pulled a million times harder than your head.
00:59:56But with supermassive black holes, that doesn't happen.
01:00:00The mass of a stellar mass black hole is concentrated in a small area.
01:00:04A supermassive black hole's mass spreads much wider, over an area a billion times larger.
01:00:11So, its gravity increases gently as you get closer.
01:00:16This means approaching a supermassive black hole feels more like walking down a slope rather than jumping off a cliff.
01:00:23So it won't rip you to shreds.
01:00:26Supermassive black holes have a bad reputation.
01:00:29That bad reputation firmly belongs to stellar mass black holes that rips things to shreds.
01:00:35The nice thing about supermassive black holes is these so-called tidal forces are much weaker.
01:00:41So I would actually be just fine and be able to take in this really bizarre scenery around a black hole
01:00:47with light from distant objects being bent out of shape.
01:00:51So, we can approach M87 star safely.
01:00:54Once there, we are faced with an awe-inspiring sight.
01:01:00The supermassive black hole distorts the light around it.
01:01:05Far away from the black hole, that warping isn't very strong.
01:01:09But the closer the light gets to the black hole, the more severely its path is distorted.
01:01:15And the starlight around the black hole becomes really bizarre.
01:01:19They get stretched into rings and arcs.
01:01:21We can even see things hidden behind the supermassive black hole.
01:01:26I would see, for example, the galaxy behind here looking completely warped out of shape
01:01:31because light is bent around the black hole.
01:01:34Black holes can even bend light so it comes from my face,
01:01:38goes around and comes back on the other side.
01:01:41So I could, in principle, use the black hole, you know, as a mirror when shaving.
01:01:44To really understand what's happening around a black hole,
01:01:48we need to understand gravity.
01:01:51And the language of gravity is the language of spacetime.
01:01:56Spacetime binds the whole universe together.
01:02:00If we could put on special spacetime glasses,
01:02:04we'd see stars, planets and galaxies floating on a grid of spacetime.
01:02:09Many stars, planets and galaxies floating on a grid of spacetime.
01:02:15These objects have mass, and mass distorts and curves spacetime.
01:02:22Imagine a trapeze artist with a flat net underneath them.
01:02:26When they fall from the trapeze onto that net, the net distorts.
01:02:30It forms a dimple right where that trapeze artist is.
01:02:33The trapeze artist is like a black hole.
01:02:35The net is like the fabric of space and time, distorting because of the mass in it.
01:02:41This distortion of the spacetime net by objects with mass is called gravity.
01:02:48The more massive you are, the more gravity you have,
01:02:53because the more you bend and stretch spacetime.
01:02:56So one trapeze artist may bend the net a little bit,
01:02:59but a hundred trapeze artists will bend that net a lot.
01:03:03And good luck trying to walk across it.
01:03:07M87 stars' immense gravity bends space, forcing light to travel along the curves.
01:03:17But what does it do to the other half of the equation?
01:03:21Time.
01:03:23Einstein realized that time actually runs slower near a black hole than back on Earth.
01:03:29It's a process called gravitational time dilation.
01:03:33Viewed from a distance, our ship appears to move in slow motion.
01:03:38But what do we see on board the craft as we approach M87 star?
01:03:44You would perceive time to proceed on normally.
01:03:48You'd look at your watch and that second hand would be going around the dial just like normal.
01:03:52But to an outside observer, that apparent one minute on your watch
01:03:55could take millions to even billions of years.
01:03:59If I'm having a Zoom conversation with mommy back home,
01:04:03even though I'm feeling I'm speaking normally, she would hear me go,
01:04:07Hi, mommy.
01:04:10And this is not some sort of illusion.
01:04:13My time really is going slower, so when I come home, she'd be like,
01:04:16Hey Max, you look so good, you look so youthful.
01:04:19And I would actually have aged less because time ran slower over there.
01:04:23On our final approach into M87 star, we reach a crucial milestone.
01:04:30We are now at the innermost stable orbit.
01:04:33We go any further, we're not getting out ever.
01:04:36You have two choices.
01:04:38You either escape to safety or you fall into the black hole.
01:04:47Well, that's easy.
01:04:49We detach the probe to approach the black hole.
01:04:52You can think of the event horizon as being the surface of a black hole,
01:04:56but that's a little bit of a misconception.
01:04:58There's not actually anything there.
01:05:00That's just the distance from the center where the escape velocity is the speed of light.
01:05:07Because nothing can travel faster than light, nothing can escape a black hole.
01:05:14Think of the event horizon as a white hole.
01:05:17Think of the event horizon as a black hole.
01:05:19Think of the event horizon as a waterfall.
01:05:23If you imagine the flow of water over a waterfall,
01:05:27if you're a fish, you can swim up close to that edge and still escape.
01:05:32But if you go too far, you hit the point of no return and you're going over.
01:05:38At the event horizon, the water moves faster than the fish can swim or our probe can orbit.
01:05:44So the waterfall, or gravity, carries them over and into the black hole.
01:05:51But what about the light around them?
01:05:55Imagine that fish that's going over the waterfall is carrying a flashlight.
01:06:00Say it's an alien fish.
01:06:02At a black hole, if that fish goes over that event horizon,
01:06:07not only does the fish and the flashlight get sucked in,
01:06:10but the light of the flashlight gets sucked in.
01:06:15There's nothing that can turn around.
01:06:17Light, matter, cows, elephants that passes through the event horizon can never come back out.
01:06:23It is a one-way ticket.
01:06:25A one-way ticket through the event horizon.
01:06:28Back on the ship though, we don't see the probe enter the supermassive black hole.
01:06:35Instead, from our perspective, the probe just gets slower and slower and slower and slower.
01:06:45Until it appears that time simply stops for the probe, frozen by the enormous gravity of M87 star.
01:06:56The probe appears stuck, glued to the surface.
01:07:00But that's just our perspective.
01:07:02In reality, the probe has already crossed the event horizon and is inside the black hole.
01:07:11If only it was that simple.
01:07:12The two major theories that explain how the universe works don't work at the event horizon.
01:07:20General relativity says the probe enters the black hole.
01:07:24But quantum mechanics throws up some major hurdles.
01:07:29According to some ideas rooted in quantum mechanics, there may be something called a firewall.
01:07:36A wall of quantum energies that prevents material from actually reaching through the event horizon.
01:07:47Our probe is approaching the event horizon of M87 star.
01:07:53But there's a problem.
01:07:55The two major theories that explain how the universe works don't agree about what happens next.
01:08:02One says the probe passes through unscathed.
01:08:06The other theory says that's impossible.
01:08:10It suggests the probe hits an impenetrable barrier called a firewall.
01:08:16How can the same event have two different outcomes?
01:08:21There's a really interesting puzzle right now, which is where general relativity and quantum mechanics meet.
01:08:28And it's called the black hole information paradox.
01:08:32What we have is this very schizophrenic situation in physics, where we have two theories that just don't get along.
01:08:39Einstein's theory of gravity explains all the big stuff.
01:08:42Quantum field theory explains all the small stuff.
01:08:45So which one is right and which one is wrong?
01:08:48This is the mystery.
01:08:52General relativity says in theory, crossing the event horizon is no big deal.
01:08:58If you're passing through the event horizon, you wouldn't notice anything different.
01:09:04You can, in fact, cross the event horizon of a black hole like M87 star in your spaceship without even knowing that you have.
01:09:14Nothing would change. You just peacefully drift inside.
01:09:19According to general relativity, our probe crosses the event horizon and enters the black hole.
01:09:27Quantum mechanics sees it differently.
01:09:30When it looks at the probe, it doesn't see a robotic spacecraft.
01:09:35It sees information.
01:09:38Everything at a quantum mechanical level has information.
01:09:42You can think of things like a particle having a charge. Particles have spin, angular momentum.
01:09:46And that information, as far as we understand, can't be destroyed.
01:09:53What do we mean by destroyed?
01:09:56Well, think of burning a book.
01:09:59The words are information.
01:10:01As each page burns, the words disappear.
01:10:06The information's gone, but not really.
01:10:09If you could track every single thing that was happening, track each smoke particle, put everything back together again,
01:10:15in principle, that information is still there.
01:10:19Because information can't be destroyed.
01:10:22The probe's information, even if mangled, should be inside the supermassive black hole.
01:10:29If the information that fell into a black hole just stayed locked inside of a black hole, that'd be fine.
01:10:36That doesn't violate any physics.
01:10:38But Stephen Hawking threw a wrench in the works when he theorized that, over time, black holes evaporate,
01:10:46slowly shrinking, particle by particle, emitting heat, known as Hawking radiation.
01:10:55Hawking radiation itself doesn't carry any information out.
01:11:00And Hawking radiation eventually destroys a black hole.
01:11:04Eventually the black hole evaporates and disappears.
01:11:08As the black hole vanishes, so too does information about the probe.
01:11:12This is a big problem for quantum mechanics.
01:11:16Can black holes really destroy information, even though quantum physics suggests you cannot?
01:11:24So, is the foundation of quantum mechanics wrong?
01:11:28This is the quantum information paradox.
01:11:31To try to prevent this impossible situation, scientists came up with a workaround.
01:11:37Something that prevents the probe's information from ever entering the black hole.
01:11:42The firewall.
01:11:44Quantum mechanics says that there is this quantum fuzz causing there to be ridiculously high temperatures
01:11:53literally burning you up as soon as you enter.
01:11:56If the firewall incinerates the probe, then its information will stay in the ashes of the ship.
01:12:02Just like the words from the burning book.
01:12:07So, which theory is right?
01:12:10Does the probe safely enter the black hole?
01:12:14Or does the probe burn up?
01:12:18I've actually spent an afternoon at Caltech arguing with people about whether anything falls into a black hole or not.
01:12:23And the answer is we don't really know.
01:12:25To find an answer, scientists have come up with some crazy ideas.
01:12:31One, called quantum entanglement, suggests that the probe is both inside and outside the black hole.
01:12:39It's information carried by particles constantly popping up on either side of the event horizon.
01:12:46So, what's the problem?
01:12:48It's information carried by particles constantly popping up on either side of the event horizon.
01:12:57And Stephen Hawking, whose original idea that black holes lose information through heat, also came up with a solution.
01:13:06He suggested that black holes have soft hair.
01:13:11Traditional black hole science says they're bald.
01:13:14By which we mean that they have no features at all, except their mass and their charge and their spin, that you can measure from outside.
01:13:23Hawking's updated theory says that black hole hair is made from ghostly quantum particles, which store information.
01:13:32Thermal radiation from the evaporating black hole carries this information away from the event horizon.
01:13:40If Hawking is right, the probe's information will eventually escape into the universe.
01:13:48The concept of black hole hair would solve the black hole information paradox, if it exists.
01:13:57But we don't know if black holes have hair, or if they're, you know, bald.
01:14:02Until we can unite quantum mechanics and general relativity at the event horizon,
01:14:09the information paradox will remain a problem for physicists.
01:14:14It's one of the most embarrassing problems in physics, which is still unsolved.
01:14:19I hope one of you who watches this will become a physicist and solve it for us, because physics is far from done.
01:14:32The failure to solve the black hole information paradox throws up a major obstacle to our understanding of how our universe works.
01:14:43This is the point where physics hits a wall.
01:14:48While a search for a solution continues, let's assume our probe dodges its way past the information paradox.
01:14:55It sails across the event horizon, towards one of the most violent places in the universe, the core of M87 star.
01:15:07It's called the singularity, and there are no rules.
01:15:13Nothing makes sense, and nothing escapes.
01:15:26Our probe has crossed the event horizon.
01:15:30It's on a one-way trip to the heart of the supermassive black hole, M87 star.
01:15:37Anything that crosses the event horizon is not coming out.
01:15:42It's like Vegas. What goes in a black hole, stays in a black hole.
01:15:47The probe leaves the physics we understand, and enters the world of physics.
01:15:52We do not.
01:15:55This probe is now moving faster than light, or being carried by space itself faster than light.
01:16:02Once you cross the event horizon of a black hole, your future lies on the singularity in the center of the black hole.
01:16:10There's no escaping the fact that you will eventually join the singularity.
01:16:14The space inside of a black hole is like a 3D spinning vortex. The space in there is always moving.
01:16:22This is the nightmare version of the carousel ride.
01:16:26The whirling probe hurtles downwards, until it hits an even more bizarre region of the black hole, the inner event horizon.
01:16:38You thought the firewall was bad, but that's peanuts compared to the inner event horizon.
01:16:43Theoretical physicist Andrew Hamilton believes that all light and matter that's fallen into a black hole piles up in a tremendous collision at this location.
01:16:52The inner event horizon would be infinitely violent, because it's like the meeting point between two universes.
01:16:59This meeting point is like water falling and smashing into spray, shooting back up from the rocks at the base of the falls.
01:17:08Inside the supermassive black hole, space races in and crashes into rebounding space at the inner event horizon.
01:17:17This would be a place of death.
01:17:19Inside the supermassive black hole, space races in and crashes into rebounding space at the inner event horizon.
01:17:27This would be a place of infinite energy. It's a place where infalling material into the black hole meets outflowing material.
01:17:37Everything falling into M87 star smashes together in a monumental release of energy.
01:17:45This energy has got to go somewhere.
01:17:49It's possible that this inner event horizon is so energetic that brand new universes could be born in this space.
01:18:00But the question is, how do you actually sort of birth a new baby universe?
01:18:05The energy created at the inner event horizon could compress down into one tiny speck, which suddenly ignites.
01:18:14Sparking baby universes into life in their very own Big Bangs.
01:18:27We know that a long time ago our own universe was very small, very hot and very dense.
01:18:34It's possible that it could have been born in the inner event horizon of a spinning black hole.
01:18:40This is such a tantalizing and very hypothetical idea.
01:18:46But if it's correct, it gives us insights into the origins of our universe itself.
01:18:53Do we have strong evidence that black holes create baby universes?
01:18:58No.
01:19:00Do we have strong evidence that they don't?
01:19:03No.
01:19:04If the probe survives the inner event horizon, it then heads towards the strangest place in the universe.
01:19:13The core of a supermassive black hole.
01:19:17The singularity.
01:19:19As the probe gets closer and closer to the singularity, the probe gets further and further away from known physics.
01:19:27We don't know what the probe will encounter when it reaches the singularity.
01:19:32We don't know what it will find.
01:19:34We don't know what it will experience.
01:19:37We don't know.
01:19:40In other words, there's a lot we don't know.
01:19:43Like, what exactly is the singularity?
01:19:47It's a hard question to answer.
01:19:50Traditional science says it's an infinitely tiny point.
01:19:53Traditional science says it's an infinitely tiny point.
01:19:57But that's not the case with M87 star.
01:20:01What's interesting is that if your black hole is spinning, the singularity is not a point, but it's in fact a ring.
01:20:08Physics says the singularity is infinitely dense.
01:20:14A point of space and time that is collapsed as far as it will go.
01:20:18It basically has infinite density in zero size.
01:20:22For many scientists, that's a big problem.
01:20:27I do not like singularities.
01:20:32I feel that they sound really unphysical.
01:20:37The word singularity sounds so intimidating and scientific, but it's honestly just our physicists' code word for, uh, we have no clue what we're talking about.
01:20:47Where else in nature do we find infinities?
01:20:51We're talking about a region that would have infinite density and infinitely small volume.
01:20:58Basically, zero volume.
01:21:00How could that exist? I just don't see it.
01:21:02We just don't know. And frankly, we will never know for sure.
01:21:07Perhaps the probe breaks up and joins material consumed by M87 star over billions of years.
01:21:15Compressed down, not just to atoms, but to a sea of energy.
01:21:22Absorbed into a ring of zero volume and infinite density.
01:21:32Or there could be another possibility.
01:21:35Maybe the singularity doesn't destroy the probe at all.
01:21:39Maybe the probe travels straight on through and passes into another universe.
01:21:53Our voyage to the heart of M87 star has been a wild ride.
01:21:59We crossed the event horizon and fell towards the singularity.
01:22:03The core of the supermassive black hole.
01:22:08Is this the end of our journey, or just the beginning?
01:22:12It could be that the singularity isn't the end point of the probe's journey.
01:22:18It could be that the probe passes through the singularity and enters into a new universe.
01:22:27Our probe has been able to cross the event horizon.
01:22:31Our probe has another option.
01:22:34An escape route out of M87 star.
01:22:39In our universe, we have black holes.
01:22:42Objects where if you enter, you can't escape.
01:22:46It's also theoretically possible for there to be white holes.
01:22:50Objects that you can't enter, you can only escape from.
01:22:55A white hole is basically a black hole running backwards.
01:23:01Some physicists have theorized that white holes may link to the singularities of black holes.
01:23:07Connected by something called a wormhole.
01:23:12There have been interesting papers written suggesting that you can have a wormhole
01:23:17where something that falls into a black hole here comes out of a white hole somewhere else.
01:23:22It sounds like a great way for the probe to escape certain death.
01:23:27Theoretically.
01:23:29A wormhole is the bridge in space time between those two things.
01:23:33It's easy to create in mathematics.
01:23:36It very well might not exist in real life.
01:23:39And we'll almost certainly live out on our entire civilization and never know about it.
01:23:43That's because constructing a bridge between a black hole and a white hole creates a few issues.
01:23:50A, we don't know how to build them for sure.
01:23:53B, they might be unstable and collapse on themselves immediately
01:23:56unless you have some new weird sort of matter that can support them.
01:24:00The problem is that it's hard to maintain this bridge open.
01:24:05It's not likely that they would ever have any practical use because they're just not stable.
01:24:13But if M87STAR does have a stable wormhole linked to its singularity,
01:24:18where might our probe end up?
01:24:20It could be that this probe's journey doesn't end at the singularity.
01:24:25And all the information that it carries with it could be deposited in some distant corner of our own universe.
01:24:34Or perhaps in a different universe.
01:24:38One idea that sounded like science fiction decades ago is actually now considered potential reality.
01:24:45And that's the idea of parallel universes.
01:24:49If parallel universes exist, then some surmise that a black hole could be a gateway to a parallel universe.
01:25:03The concept of parallel universes comes from inflation theory.
01:25:07The model we use to explain the first moments of our universe.
01:25:14The most mainstream and accepted theory for how our Big Bang happened is inflation.
01:25:20A process whereby a tiny bit of space just keeps doubling, doubling, doubling, doubling.
01:25:25Giving us this.
01:25:27And the universe expanded so much, you could have created bubbles in a world
01:25:31It's almost like, you know, trying to boil water and you turn your burner on really high, right?
01:25:35You start to create these bubbles.
01:25:37And these bubbles could be these own island universes that are foaming up in this endless multiverse.
01:25:44If there are parallel universes, who knows which one our probe may end up in?
01:25:50This universe may be just like our own.
01:25:53Or it might be something entirely different.
01:25:56We'll never get to find out unless we follow in after it.
01:26:02It could all work out just fine.
01:26:05And that probe just sails on through and gets to explore new adventures.
01:26:10We don't know.
01:26:12Only the probe knows.
01:26:18So, what do you think?
01:26:20Only the probe knows.
01:26:26Supermassive black holes are some of the strangest and most fascinating objects in the universe.
01:26:33Ever since Einstein's theory of relativity predicted black holes a century ago,
01:26:40we've been trying to understand how they work.
01:26:43The photograph of M87 star confirmed many theories.
01:26:47But there's still much to learn about the birth, life and death of these remarkable objects.
01:26:55And even more to leave us fascinated.
01:27:00This is the ultimate unknown.
01:27:02This is the real Wild West.
01:27:04This is the frontier of human knowledge.
01:27:09I care about supermassive black holes first and foremost because they are awesome.
01:27:14They stimulate my childhood imagination and fascination.
01:27:21Supermassive black holes offer us a truly unique window into how the laws of physics work,
01:27:27especially the laws of gravity in extreme regimes far beyond anything that we can possibly imagine here on Earth.
01:27:34Supermassive black holes lurk at the heart of almost every large galaxy that we know of.
01:27:39So in some way, we're just sort of all along for the ride with the supermassive black holes.
01:27:44If I could make a request for one special favor I would get before I die,
01:27:52what I would like to do is to get to just spend a few hours orbiting the monster black hole in the middle of the galaxy.
01:28:01What a way to go.