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| The Riddle of Black Holes |
The notion of a black hole is a natural extension of the laws of gravity. The whole Earth is pulling on a rocket ship, and all it has to do is go 7 miles per second to escape from the Earth. And to get all the way to a black hole, you'd have to crunch down the entire sun to be less than a few kilometers across. Now it would take something traveling greater than the speed of light to escape, so nothing can escape, and the whole object goes dark. Christian Ott, an astrophysicist at the California institute of Technology, has been trying to understand how such strange entities as black holes might really form in the cosmos. But what interests black-hole researchers is not the explosion. It's what happens at the very center of the dying star. Modern astronomers have never witnessed a star in our own galaxy explode. But theoretical physics predicts that if a star is large enough, its collapsing core should shrink down to form a black hole.
And it will continue to collapse down until it forms a black hole. But do such strange crushed corpses of stars really exist out in the cosmos? Could they be lurking at the center of some of those clouds of gas and dust thrown off in a supernova? Christian Ott and his theoretical-astrophysicist group at caltech are trying to discover whether exploding stars really do form black holes. Well, I just generally you know, I'm really excited about stars that blow up, actually. First of all, to get a black hole, you need low, specific angular momentum. To have a critically spinning black hole, you need a lot of angular momentum. Simulating supernovae stellar collapse and black-hole formation is so hard because it brings together a lot of physics. It's general relativity for gravity. It's fluid dynamics for the gas that collapses. It's particle physics. Doing the simulations, it's like trying to do a really good weather forecast. So far, Christian has failed to make a virtual star explode in a way that looks like a real supernova. But after years of refining the physics and the math, he now thinks he may be the first to fully understand how a black hole is born. Man, that is an event horizon right there, and this black hole in the center. That's the first time that we do see this. What's surprising is that the most promising simulations don't actually explode. They simply collapse. It's not a bang but a whimper. Its name not supernova, but unnova. It's basically just everything eventually sinks into a black hole, and the star slowly but surely just disappears. It could be true that most stars, or a large fraction of stars, just disappear.
We don't have any data on that. We have never seen an unnova. If Christian is right and black holes form silently, then these cosmic cannibals could be hidden in plain sight all around us, and we might never know it. Finding black holes is terribly, terribly difficult. Even if it wasn't black and would be radiating energy, it would still be only, let's say, 20 miles across. And even, you know, at 10 light-years away, it would be impossible to find even with the best telescopes we have. But if black holes are almost completely elusive, no one told this man. He's spent the past 30 years hunting one, a giant one, right at the heart of our own Milky Way galaxy. Astronomers call it a supermassive black hole. But despite the enormity of this discovery, it would be just the first of many increasingly bizarre and disturbing findings. The next was to figure out what goes on inside a black hole. What happens to stars, planets, even people if they get too close to this cosmic sinkhole? No telescope can ever see inside black holes. To understand how they twist reality, we have to stop looking and learn how to listen. Lurking at the center of our galaxy is an object that's completely invisible but weighs as much as four million stars. Astronomers now believe almost every galaxy has a supermassive black hole at its core. So, what are they? Science fiction sees black holes as cosmic time machines or portals to a parallel universe. But real scientists are finding that truth is stranger than sci fi. You're about to enter a world where the very big and the very small are indistinguishable, where reality and illusion are one and the same.
The Riddle of Black Holes - picture Astronomer Julie Comerford has been studying the centers of dozens of distant galaxies, trying to find signs of black holes, hoping to learn more about these mind-bending objects. It turns out that in all or nearly all galaxies, wherever we look, they have a central supermassive black hole at their heart. Supermassive ones are the ones that have masses of anywhere from a million to a billion times the mass of the sun. You can see a supermassive black hole when gas is falling onto it. And sort of right before the gas falls into it, it gets heated up and emits a lot of energy and can appear really bright. But when Julie investigates the glowing gas surrounding these giant black holes, she finds something totally unexpected. There's a cosmic dance going on on a scale that's almost unimaginable. You saw two peaks in the light instead of just one. You'd expect one from one black hole that's just sitting at rest in its galaxy, but we saw two peaks with different velocities. And that immediately hit us, as this has got to be something interesting. Julie began thinking about what would happen when two galaxies collide. And if both had black holes at their centers, what would happen to those massive objects? So, when two galaxies collide, the black holes at their center instead of crashing in head-on, they begin this swirl, or dance. And the way that we can detect these waltzing black holes is by looking at the light that's emitted from them. So, for the black hole that's moving towards us, we detect light that is at smaller wavelengths, scrunched up together, so we see bluer light. And for the black hole that's moving away from us, we see stretched-out, longer-wavelength light that appears redder. So it's this redder and bluer light that is a telltale signature of a black-hole waltz. Every time we see it, we high-five in the observation room, and you just can't get over it. As Julie scans the universe, she finds the same remarkable dance happening time and time again.
In galaxy after galaxy, black holes are paired up and dancing the cosmic night away. So, we identified 90 galaxies from when the universe was half its present age, and we found that fully 32 of them, or about a third, had black holes that exhibited this blue-and-red signature. So that was really surprising that such a high fraction of the black holes were not stationary at the center of the galaxy at all, that they were undergoing this waltz with another black hole. Scientists like Janna Levin believe the discovery of waltzing black holes opens up a whole new way to learn what's inside them, because their dance might not only be visible. It could also be audible. The scientific visionary Albert Einstein saw space and time as a flexible material that could be distorted by gravity. A black hole is merely a very deep well in this material. When two black holes come close to one another, these two orbiting wells stir up space-time and send out ripples that can travel clear across the universe. And these waves will move out through the universe, traveling at the speed of light. So we can hope to not see black holes with light but maybe, in some sense, hear them if we can pick up the wobbling of the fabric of space-time itself. For the past several years, Janna and her colleagues have been trying to predict the sounds black holes make as they spin around one another. The calculations are not for the faint of heart. Modeling what happens when two giant objects create a storm in the sea of space-time takes some serious math and months of supercomputing. This is the orbit of a small black hole around a bigger black hole, and it's literally making a knocking sound on the drum, where the drum is space-time itself. Well, it really sounds like sounds like a knocking. It starts to get a higher frequency and happen faster, until it falls into the big black hole and goes down the throat. And then the two will ring out together and form one black hole at the end of the day. And then it just sort of, you know, "brr," chirps up. Because black holes stir up the space and time around them so much, the orbit of one black hole around another looks nothing like the orbit of Earth around the sun. An orbit can come in around a black hole and do an entire circle as it loops around before it moves out again. Black holes are like fundamental particles, and that's very surprising because they're huge, macroscopic objects. Right now, this idea is only a tantalizing hunch. But in just five years, super-sensitive detectors should be able to pick up the ripples in space created by two massive black holes spinning around one another. And they'll tell us whether they really do behave like tiny atoms. But this connection between the very big and the very small has already sparked a war between two of the greatest living physicists. One of them is Stephen Hawking. The other began life as a plumber in the South Bronx and is now using black holes to develop the most revolutionary idea in physics since Albert Einstein - an idea that literally turns reality inside out. Black holes are the most massive objects in the universe. Around a black hole, there is an invisible line in space called the event horizon. Outside that line, the hole's gravity is just too weak to trap light. Inside it, nothing can escape its pull. If a pair of virtual particles fmed just outside the event horizon, then one of the pair might travel across that point of no return before being able to recombine, falling into the black hole and leaving its partner to escape as real radiation Hawking radiation. If Hawking is right, black holes should not actually be black. They should shine ever so faintly. No one has ever detected Hawking radiation from the rim of a black hole. In fact, it's so faint, and black holes are so far away, that it will probably never be possible. But Jeff Steinhauer thinks he's found a way to test Hawking's theory and send shock waves through the world of physics. He's the only person on the planet who has seen a black hole from up close. In fact, he's learned how to create one. My black hole is in no way dangerous. It's a sonic black hole that can only absorb sound waves. It's only made of 100,000 atoms, which is very little matter. And I'm sure that my neighbors would love that I would put a sonic black hole around my apartment, but it's not gonna happen. When he's not jamming in the basement of the physics department at the Technion in Israel, he's upstairs in his lab. Jeff Steinhauer's recipe for making a sonic black hole begins with a tiny sample of rubidium atoms chilled down to minus 459 degrees fahrenheit. While I was working with these very cold atoms, I stumbled across a phenomenon. When the atoms are actually flowing faster than the speed of sound, then, if there are sound waves trying to travel against the flow, they can't go forward. And this is analogous to a real black hole, where light waves cannot escape due to the strong gravitation. Even though this black hole traps only sound, not light, the same laws of quantum mechanics apply to it as they do to its cosmic cousins. If Hawking's theory about black holes is correct, Jeff should be able to detect tiny sound waves escaping. The analogy that I've used over and over about black holes is water going down a drain. The invention of string theory, which has a lot to do with tubes - some people even say this must've been Susskind the plumber. Leonard Susskind's fascination with black holes began 30 years ago when he listened to a talk by Stephen Hawking - a talk that triggered a violent reaction. I first heard Stephen Hawking give a lecture up in San Francisco, in which he made this extraordinary claim that black holes seem to violate the very, very fundamental principle of physics called conservation of information. Seven years after his groundbreaking work on black-hole radiation, Hawking had taken the idea to its logical conclusion. For every ounce of material a black hole absorbed into its core, it would radiate away an equivalent amount of energy from its event horizon. But since there is no physical link between the center of a black hole and its event horizon, the two processes could not share any information. What happens when the information goes down the black hole? If what Hawking claimed was right, it would mean most of modern physics had to be seriously flawed. Black holes would spend their lives eating stars and leave no record of what they'd done. Nothing else in the universe does this. The fiery blast of a nuclear bomb might vaporize everything in sight, but all that information is still in this universe, no matter how scrambled. Black holes, according to Hawking, don't scramble information. They completely destroy it. That was 1981, and from that time forward, I was hooked. I could not let go of the question of black holes. This squabble soon grows beyond these two men and engulfs all of physics. At stake is more than just bragging rights for the winner. It turns out to affect the very way we perceive the universe. There may be 100 million black holes scattered across the Milky Way. Anything that strays too close to these dark remnants of burned-out stars will be pulled in by an intense gravitational field. But what actually happens to the stuff that falls into a black hole? Is it simply wiped out of existence, or do black holes remember? These are the battle lines of the black-hole war - a battle with repercussions that the men who started it could never have imagined. It's a war between two giant minds. On one side, the famous physicist Stephen Hawking, on the other, Leonard Susskind, one of the creators of string theory, a notoriously difficult branch of physics. Stephen Hawking argues black holes destroy what they swallow without a trace. Leonard Susskind passionately disagrees. But for 10 years, he struggled to find anything wrong with Hawking's concept of how black holes radiate away the matter they swallow. It was thought to be inconceivable that somehow the things which fell into the black hole could have anything to do with the Hawking radiation, which was coming out from very, very far, from where the particles fell in. In 2004 at a scientific conference in Dublin, Hawking conceded defeat. Black holes do not destroy information. Leonard Susskind had won the black-hole war. But he'd done much more than that because the theory does not merely apply to black holes. A black hole raises these challenges and really sharpens these challenges because it's practically a place where ordinary space doesn't exist anymore. So, if I'm asked questions about how space emerges, I will simply have to say, well, we're thinking about it. We don't understand it. Black holes have been a source of fascination for almost a century. We've thought of them as time machines, shortcuts to parallel universes, as monsters that will one day devour the Earth. Well, any of these ideas may turn out to be true one day. But right here, right now, black holes have a profound effect on you and me. Their shimmering, holographic surfaces seem to be telling us that everything we think is here is mirrored out there at the very edge of our mysterious universe.
Also you can watch online the others episodes of Through the Wormhole documentary movie film as Through The Wormhole: Is There A Creator?, Is Time Travel Possible?, What Happened Before the Beginning?, How Did We Get Here?, Are We Alone?, What Are We Made Of?, Beyond The Darkness.
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