Originally posted by Raithere
No need to take my word for it, here’s a very nice site that explains black-holes in plain English (I’ve included some snippets below too):
http://amazing-space.stsci.edu/reso...background.html
5. Is a black hole a giant cosmic vacuum cleaner?
The answer to this question is "not really." To understand this, first consider why the force of gravity is so strong close to a black hole. The gravity of a black hole is not special. It does not attract matter differently than any other object does. At a long distance from the black hole the force of gravity falls off as the inverse square of the distance, just as it does for normal objects.
Mathematically, the gravity of any spherical object behaves as if all the mass were concentrated at one central point. Since most ordinary objects have surfaces, you will feel the strongest gravity of an object when you are on its surface. This is as close to its total mass as you can get. If you penetrated the spherical object, getting closer to its core, you would feel the force of gravity get weaker, not stronger. The force of gravity you feel depends on the mass that is interior to you, because the gravity from the mass behind you is exactly canceled by the mass in the opposite direction. Therefore, you will feel the strongest force of gravity from an object, for example a planet, when you are standing on the planet's surface, because it is on the surface that you are closest to its total mass. Penetrating the surface of the planet does not expose you to more of the planet's total mass, but actually exposes you to less of its mass. Now remember the size of a black hole is infinitesimally small. Gravity near a black hole is very strong because objects can get extremely close to it and still be exposed to its total mass.
There is nothing special about the mass of a black hole. A black hole is different from our ordinary experience not because of its mass, but because its radius has vanished. Far away from the black hole, you would feel the same strength of gravity as if the black hole were a normal star. But the force of gravity close to a black hole is enormously strong because you can get so close to its total mass!
8. When were black holes first theorized?
Using Newton's Laws in the late 1790s, John Michell of England and Pierre LaPlace of France independently suggested the existence of an "invisible star." Michell and LaPlace calculated the mass and size — which is now called the "event horizon" — that an object needs in order to have an escape velocity greater than the speed of light. In 1967 John Wheeler, an American theoretical physicist, applied the term "black hole" to these collapsed objects.
9. What evidence do we have for the existence of black holes?
Astronomers have found convincing evidence for a supermassive black hole in the center of the giant elliptical galaxy M87, as well as in several other galaxies. The discovery is based on velocity measurements of a whirlpool of hot gas orbiting the black hole. Hubble Space Telescope data produced an unprecedented measurement of the mass of an unseen object at the center of the galaxy. Based on the kinetic energy of the material whirling about the center (as in Wheeler's dance, see Question 4 above), the object is about 3 billion times the mass of our Sun and appears to be concentrated into a space smaller than our solar system.
For many years x-ray emission from the double-star system Cygnus X-1 convinced many astronomers that the system contains a black hole. With more precise measurements available recently, the evidence for a black hole in Cygnus X-1 is very strong.
~Raithere [/B]
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