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Monday, 15 February 2016

10 FASCINATING FACTS ABOUT BLACK HOLES


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10 Fascinating Facts About Black Holes
By Robert Grimminck,
Toptenz, 15 February 2016.

Black holes were first theorized by John Michell in 1783, and the theory was pushed forward in 1915 when Albert Einstein published his general theory of relativity, in which he theorized their formation. Their existence wasn’t confirmed until 1971. Since then, research has continued into these mysterious regions that are sprinkled throughout the known universe.

10. Three Types of Black Holes

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The first type of black holes is called stellar black holes (pictured above) and they are the smallest of the trio. They are created when a star that is larger than our sun collapses and continues to fall in on itself. While stellar black holes are relatively small, they are incredibly dense. For example, three times the mass of the sun can be packed into the area that is the size of a city on Earth. It is believed that there are a few hundred million stellar black holes in our galaxy.

On the other end of the size spectrum are supermassive black holes. Researchers aren’t sure how they are spawned, but their radius is about the size of the sun and their masses are billions of times greater than the sun. It is believed that they are at the center of galaxies, including our own.

Finally, intermediate black holes are mid-sized black holes. It is believed they are formed when there is a chain reaction collision of stars that are in a cluster. Researchers weren’t even sure that these existed until one was discovered in 2014.

9. What Do they Look Like?

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Black holes can’t be observed because nothing, not even light, can escape from their boundaries, known as the event horizon, because the gravity is so strong. What we could observe is gas when it falls into a black hole because it is heated up, which causes the gases to glow. If we had telescopes or satellites to see a black hole up close, it would look like a rotating disk with a black hole in the middle.

8. Colliding Black Holes


On September 14, 2015, twin Laser Interferometer Gravitational-wave Observatory (LIGO) detectors picked up a small chirp from space. It turns out that chirp was a collision 1.3 billion years ago between two black holes a billion light years away. The black holes were about 29 and 36 times the mass of our sun. Before colliding, they circled each other and then in a fifth of a second, they became one black hole with the mass of 62 of our suns. When they combined, some of the mass was converted to energy and the energy emitted was gravitational waves. Gravitational waves were first theorized by Einstein, and they are a disturbance in the cosmos that could cause space-time to stretch, jiggle, and collapse, which would produce ripples of gravity. The problem was that there was no way to detect these gravitational waves and physicists, including Einstein himself, were never really sure they existed.

The discovery has already been hailed as one of the biggest scientific breakthroughs of the past century and Stephen Hawking said it is a key scientific moment that could change how we look at the universe.

7. Time Slows Down Around it


If you’ve seen Interstellar, you’ll know what happens when you travel near a black hole; time slows down. What is incorrect about the film is that the time dilation would not be quite that extreme.

Time dilation is ultimately affected by gravity, the stronger the gravity, the stronger the time dilation. Also, time only slows down once you get near the black hole; once you pass the event horizon, time would stop.

6. What’s at the Center?

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It is believed that the very center of a black hole is a time space curvature called singularity. As you get closer to singularity, large amounts of matter are crushed and jammed into immensely small and dense space. In fact, in singularity, matter is crushed to the point where it doesn’t even have dimensions. Singularity also grows infinitely bigger the farther objects travel into it. But since the insides of black holes are impossible to observe, singularity is only a theory and some physicists even question if it exists at all.

5. Closest Black Holes


Since black holes are so hard to detect, we aren’t exactly sure where the closest one is. At first, researchers believed the closest one was at the center of the Milky Way, but currently it is believed that V616 Mon (A0620-00) in the Monoceros constellation, about 3,000 light years away, is the closest black hole.

4. Energy Source

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At first, it was believed that black holes were just energy drains because once something crosses the event horizon, it never leaves. But in the 1970s, Stephen Hawking showed that black holes should also emit power around the event horizon through a radiation, known as Hawking Radiation, and it is produced by quantum fluctuations of empty space. The obvious extension is: would we ever be able to harness that power? Well, some physicists believe that if we overcame the physical problems it would be possible to get energy from a black hole.

In 1983, a team of physicists suggested that an energy collecting device could be dropped in close to the event horizon and then we could simply pull it back up. It would be similar to getting water from a well with a rope and bucket. Obviously, you’d need a very strong bucket and rope to avoid being sucked in by the event horizon. Another way to collect energy would be to stick in “strings” and the radiation would run up it, the way oil runs up a wick in a gas lamp.

3. Could We Create One?


It goes without saying that black holes can be dangerous, so we definitely wouldn’t want to make one on Earth, right? Well, it turns out that we can theoretically make microscopic ones that are harmless. In 2014, using Hawking Radiation, researchers came close to mimicking a black hole in a lab. But at the time of this writing, one has not been created.

2. Evaporate Over Time


In the prior entries we talked about Hawking Radiation, which is energy found at the boundaries of the black hole. What is interesting is that this radiation also causes black holes to evaporate over long periods of time.

Why they evaporate comes down to quantum theory which suggests that virtual particles pop in and out of existence all the time. When they pop into existence, a particle and an antiparticle combine and then they disappear again. But when the two particles pop into existence near the event horizon, they don’t cancel each other out. Instead, one falls into the black hole and the other goes off into space. Over time, the escaping particles cause the black hole to deteriorate. That means black holes die, just like everything else in the known universe. Except for Keith Richards, of course.

1. What Happens When You Fall In

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If you were to dive into a black hole that was the size of the Earth, your body would look like “toothpaste” coming out of a tube. Your body would be stretched out in what British astrophysicist, Sir Martin Rees, called “spaghettification.” Eventually, you would become a stream of subatomic particles that would swirl into the black hole. But, if you were to dive into a larger black hole, say one that is the size of our solar system, then your body may be able to hold its structural integrity.

If you survive that, you’ll see the curvature of space-time and you will be able to see everything that fell into the black hole before you and at the same time you’ll be able to see everything that will ever fall into the black hole. This means that you’ll be able to see the entire history of the universe, from the Big Bang to the end of time, all at once.

Top image: Artist’s impression of a supermassive black hole at the centre of a galaxy. Credit: ESO/L. Cal├žada.

[Source: Toptenz. Edited. Top image added.]

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