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Black holes 2 (Click to select text)
Black Holes What are black holes? Black holes are the remains of a massive star that has collapsed and shrunk to a tiny point in space. They have all of the gravity of the star concentrated into a miniscule point many times smaller than the original. Black holes are difficult to see because they are spinning faster than the speed of light. This causes all light to be pulled to them leaving no refractions to be seen by the naked eye. The only way to actually “see” a black hole is through the clues they give off. Where do black holes come from? Black holes are formed when giant stars run out of fuel and are overwhelmed by their own gravity. When this happens they cannot keep from collapsing. After stars collapse, they start rotating and as they are spinning, their gravity becomes stronger causing them to shrink. As the object becomes smaller, it starts spinning faster and faster. Then the core compacts into a mathematical point with virtually zero volume, where it is said to have infinite density. This is referred to as a singularity. When this happens, escape would require a velocity greater than the speed of light. No object can reach the speed of light. The distance from the black hole at which the escape velocity is just equal to the speed of light is called the event horizon. Anything, including light, that passes across the event horizon toward the black hole is forever trapped. Using a small black marble as an example to represent the size that the Earth would become if it collapsed and became a black hole, Todd R. Lauer, of the National Optical Astronomy Observatories said, " Black holes are very messy eaters. If you took that marble to an 'all-you-can-eat buffet' allowing it to consume all the matter around it, the feeding frenzy would produce as much radiation as the Sun." Research indicates that black holes may have existed at the beginning of time. Black holes are so dense that not even light can escape. Looking towards a black hole, the stars behind it would appear out of place because black holes distort light. The immense gravitational pull of black holes is thought to be responsible for the swirling masses of stars in spiral galaxies throughout the universe. Gravity in a black hole should be able to pack stars in so tight that the intensity of the stars' light would drastically increase towards the center of gravity. Everything falling into a black hole loses its identity, you couldn't tell if it were a satellite or a T.V. set that fell in. If you were to enter a black hole, you would find you watch ticking along at the same rate as it always had (assuming both you and the watch survived the passage into the black hole). However, you would quickly fall toward the center where you would be killed by enormous tidal forces (e.g., the force of gravity at you feet, if you fell feet first, would be much larger than at you head, and you would be stretched apart). Although your watch as seen by you would not change its ticking rate, just as in special relativity (if you know anything about that), someone else would see a different ticking rate on your watch than the usual, and you would see their watch to be ticking at a different than normal rate. For example, if you were to station yourself just outside a black hole, while you would find your own watch ticking at the normal rate, you would see the watch of a friend at great distance from the hole to be ticking at a much faster rate than yours. That friend would see his own watch ticking at a normal rate, but see your watch to be ticking at a much slower rate. Thus if you stayed just outside the black hole for a while, then went back to join your friend, you would find that the friend had aged more than you had during your separation. Earth's escape velocity, the speed it takes to escape the pull of gravity, is 11 kilometers per second. The escape velocity of a black hole is 300,000 kilometers per second, which is faster than the speed of light. If Earth's diameter shrank to less than 1 centimeter, the escape velocity would exceed the sped of light, the escape velocity of a black hole. Anything can become a black hole if you compress it enough. Black holes technically can't be seen, but they give off many clues to their location. Signs of many black holes have been located during normal observation of other space objects. Abnormally high levels of X-rays and gamma rays are the most common clues, but other exotic energy sources are also good clues. Astronomers have also located black holes by studying the speeds of swirling galaxies. If large objects are moving at very high speeds astronomers usually try to track their orbits and try to locate a central object that could be the source of the gravity. Astronomers believe there may be thousands of black holes and other mysteries of space, and they hope to learn more about them in the future.
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