What has been determined is at the center of a celestial body such as a "black Hole"?
929295
It wasn't Hawking who came up with the theory, but at the core of a black hole is a body of super dense matter wherein even the space between the nucleus  of an atom and its electrons has been compressed into nothingness.\n\nImagine all the matter that composes a large cruise ship occupying a space less than the size of a tear-drop.\n\nAll still theory, though the evidence has gotten pretty convincing over the last 60 years.
573101
Small black holes will have larger tidal forces. They also have have a larger amount of Hawking radiation. The radius of a black hole is determined by the mass of the black hole. Larger black holes are typically at the centers of galaxies. Smaller black holes are more randomly positioned.
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The current scientific theory holds that black holes are formed when stars of sufficient mass (about 3x the mass of our Sun) reach the end of their life and collapse down into a singularity, which is, in essence, an infinitely small point with a huge amount of gravity - gravity so powerful that not even light can escape it's pull if it gets too close. It is also thought that black holes can be formed from smaller masses if external energy/pressure is exerted to squeeze the mass into a singularity.\nNot sure if there's any direct experimental evidence of creation, but there is evidence that they exist. Cosmologists use several different methods to detect blacks holes, such as by looking for light being bent and/or disappearing as it travels from remote stars towards us, and also by looking for bursts of x-rays that are given off as matter is sucked into the back hole and destroyed.\nFun fact: current evidence and theory suggests that the center of the Milky Way is a giant black hole that was formed as the densly packed stars in the center collapsed and sucked each other in.
724210
something like what we call a "black hole"
1062186
At the center of the universe is a giant black hole, or the remains of a singularity, or God. It is all a matter of perspective and personal beliefs.\n\nThe Big Bang theory states that all was created from a singularity, a dimensionless point of energy that burst forth in a huge explosion. As the energy dissipated it cooled and became particles which came together to create atoms, then clouds of atoms became stars, galaxies, planets and us. But did all of the energy expend itself from that singularity? Or does some of it still exist there?\n\nAstronomers now believe that every galaxy is formed around black holes. Extropolating, that would suggest that all matter is formed around a massive black hole.\n\nAnd the Creationists believe that everything was created by God and that of course God is the center of everything including the universe.\n\nBut now string theory in its latest form suggests that the universe was created by the collision of two extra-dimensional membranes. And that the comic book / science fiction concept of multiple universes may actually exist. So maybe Robert Heinlein was right all along. I wonder where the Gay Deceiver is parked now?\n\nTake your pick.
557703
Black holes are huge concentrations of mass in a very small area.  So small that it is too small to contain conventional matter as we understand it.  There is a perimeter around a black hole known as the event horizon.  Beyond this point, nothing, not even light can escape the gravitational pull of a black hole.  If you were to be able to stand on the event horizon and have telescopic vision like Superman, looking tangent to the event horizon, you would see the back of your head.
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The short answer is that whenever we take a good hard look at any given galaxy, we find good evidence that there is, or could be, a black hole at it's core.\n\nThe long answer is:\nIt is not so much a theory as something being increasingly noticed. Because black holes are the latest and coolest thing in astronomy (just look how many questions about them appear here!), everyone is always looking for them. They are not so easy to find because, well, they are black. You can't see one directly. One way to tell if there is a black hole there is by the effects of it's gravity on nearby matter. So far, the biggest effect observed on nearby matter has been high energy radiation caused by the rapid acceleration of that matter as it falls into the black hole. Some galaxies show that in their core, indicating a massive black hole there.\nAnother effect is that stars could orbit the black hole, just like the Earth orbits our Sun. We have known for a long time that all stars in a galaxy are orbiting around the center of that galaxy. IN the past it was assumed that there were enough regular stars and dust and gas in the center of the galaxy to make a mass big enough to orbit around. But recently observations with more powerful telescopes of stars closer and closer to the center of our Milky Way galaxy have shown stars VERY close to the center of the galaxy orbiting VERY fast. In that case it is easy to calculate the mass of whatever it is that they are orbiting, just like we can calculate the mass of the Sun by knowing how fast the Earth orbits it. Those calculations show the mass is millions of times more than the sun. Now we know all that mass has to be in an area smaller than the orbits of those stars, and the size of those orbits is measured as being quite small, so we know the volume far too small to be a big star cluster or other ordinary concentration of mass. The only known way to get so much mass in such a small volume is a black hole.\n\nI recall many years ago, when computers were just becoming powerful enough to do big simulations, that someone tried to simulate a globular star cluster by programming a few thousand stars to orbit in a big ball with no mass other than the stars themselves. It didn't work. The stars kind of just all dispersed at random and did not stay in a nice ball shaped globular cluster. Now it should be obvious that if there was a massive black hole in the center of the globular cluster, then all the stars could orbit it like the planets do the Sun, only not all in one plane like the planets do. And I believe some evidence of medium large black holes has been found in some globular clusters recently by the same method of using powerful telescopes to look at the orbits of stars very close to the core. And after all, what is a globular cluster but a really small galaxy.\n\nSo giant telescopes, some of them is space, are providing data never before available that just makes it more and more reasonable to assume that all galaxies have a massive black hole at the core.
1132943
a black hole is an infinitely dense point, called a singularity
23482
In astronomy, an object so massive that nothing, not even light, can escape its gravitation. Black holes were given their name because they absorb all the light that falls on them. The existence of black holes was first predicted by the general theory of relativity. Supermassive black holes have been found in the centers of many galaxies. Stellar black holes are thought to arise from the death of very massive stars. Astronomers expect to find many stellar black holes in the Milky Way. \n\n\nFiguratively, the term black hole is used to refer to a total disappearance: “They never saw the man again — he might as well have fallen into a black hole.”
958616
There appears to be a birth and death cycle within galaxies, evidenced by the black holes found in the center of many of them, including our own.
788553
The centre of mass of a system of particles (or a continuous body) is the unique point at which the entire mass of the system (or body) may be considered to be concentrated.  For many purposes the system behaves as though the mass were concentrated at the centre of mass.\n\nIn a uniform gravitational field, the centre of gravity is located at precisely the same point as the centre of mass.  So, in most everyday scenarios, the centre of gravity is the same as the centre of mass.  If, however, a system is sufficiently large that the non-uniformity of the gravitational field experienced by the system becomes significant, then the centre of gravity will be slightly displaced from the centre of mass.
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Nothing; the "hole" in space isn't like a hole in your shirt, but rather like a giant pit.  What falls in stays in (of course, this is a three-dimensional hole that sucks stuff in from all directions, but we'll stick with the hole-in-the-ground analogy for simplicity)\n\nWhat has been discovered mathematically by people like Hawking and Chandrasekhar is that black holes actually do give off radiation (so-called Hawking radiation) through its effects on local space-time right at the event horizon.  At this specific region of space, charged pairs of virtual particles appear, and every now and then, rather than rejoining and annihilating each other in a tiny flash of light, one particle escapes and goes flying off away from the black hole while the other gets drawn in.  The escaping particle is considered matter, while the one getting drawn in becomes antimatter.  As the antimatter reaches the center of the black hole, it cancels an equal mass of matter and the black hole gets infinitessimally smaller.  An old black hole (one that has consumed all the matter in its vicinity) therefore gradually "evaporates" over a VERY LONG TIME (about 10^61 times the age of the Universe for a 30 solar mass black hole!) until its mass is so small that its gravity is no longer strong enough to hold in light, and it may do any number of things -- explode, fade out and become a really big hunk of red-hot metallic stuff, sit and remain a giant, dark gravity well... depends on what kind of math you like and the current theories at the time you calculate it.
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A black hole is defined as a place where light can not escape due to the gravitational force.  The proof that they exist are the equations of gravity and experiments in labritories where miniture black holes have been created that evaporate in nanoseconds.
515493
The galaxy is everything you see at night when you look up in the sky. Stars, planets, moons, asteroids, meteors, comets, or any other terrestrial body. I think there's just one black hole at the middle of the galaxy.
429107
Our Galaxy has a bulge of stars at the center, wherein there may lie a giant black hole at the center. The galactic center lies in the direction of the constellation Sagittarius.\n\nRegular black holes are thought to form from heavy stars (perhaps those which start off with masses more than 20 or 25 times that of the Sun, but this is still an area of active research). When these stars end their lives in a supernova explosion, their cores collapse and gravity wins out over any other force that might be able to hold the star up.\n\nEventually, the star collapses so much that it is contained within its Schwarzschild radius, or event horizon, the boundary within which light cannot escape. At this point, the black hole is extremely tiny; a black hole with the mass of the Sun would fit in a small town, while one with the mass of the Earth would fit in the palm of your hand! The material inside the Schwarzschild radius will continue to collapse indefinitely, reaching the point where our understanding of the laws of physics breaks down. But no information from inside the Schwarzschild radius can escape to the outside world.\n\nSupermassive black holes, meanwhile, form differently - perhaps from the merger of many smaller black holes early in the universe's history - and grow over the years as they suck in gas from their surroundings. The formation of these objects and their relationship to the galaxy that harbors them is still an area of active research.\n\nWe have never sent anything to one.
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As moses said very well indeed, Nobody knows.\nThe major problem I have with a black hole is why it is called a black hole. If this thing is so dense and gravity is so powerful it would be bending light around at the event horizon so that you'd not even know the black hole is there. The other way to confirm this "black hole" would be to observe the planets remaining in the solar system still rotating around a sun which is not there any more. What you would actually confirm would be, according to the laws of gravitational attraction that two massive bodies are attracting each other. One is the planet you see and the other is the "black hole.\nWe know we can change things by sqeezing them, coal into diamonds etc, but there are some materials such as water that are supposed to be incompressible.\nWhat we are supposed to think is the acceleration gradient is so massive that atoms are stripped into their components.\nThe thing is, if the graviation is so massive beyond the event horizon that things are moving at the speed of light.\nThis is a contradiction according to the relativistic E=MC^2 equation.\nIn order for something to travel at the speed of light it must have no mass.\nWe know light has no rest mass.. I.e. stop some light and you get energy but nothing to look at.\nTherefore we are supposed to assume that a massive body changes into pure energy to reach the speed of light and then turn back to mass when it gets to the centre of the black hole.\nThe conclusion there is neither mass nor energy according to the laws of physics currently at the centre of a black hole.
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It is precisely that the density of a black hole is beyond the scope of reality that makes a black hole what it is - a singularity. In mathematics, a singularity is a point at which an equation cannot be solved. A simple example is 1/x, which is undefined at 0. In a black hole, the laws of physics have no solution.\n\nThe atomic bomb has nothing to do with this. Radioactive material like plutonium will explode in a runaway chain reaction if sufficient mass is brought together. (An explosive mass of radioactive material is called a prompt critical mass.) This only works with highly radioactive materials and involves no compression, whereas anything will form a black hole if sufficiently compressed. Compressing matter to this level is far beyond our current capabilities, however; it takes the collapse of a massive star to make a black hole.