|MadSci Network: Astronomy|
When material from a star falls into a black hole, it gets torn apart by the immense gravitational forces exerted upon it. Some of the matter gets converted into energy and is emitted by the black hole as X-rays (high energy photons). This is why much of our observational evidence for stellar black holes is in the form of known X-ray binary systems like Cygnus X-1 in which a normal star is orbiting around an unseen X-ray source. There has been much debate on how to describe the properties of black holes given that so little is known and can BE known about them observationally. Much of what is discussed involves understanding black holes in relation to General Relativity (how matter interacts with space and time) and Quantum Mechanics (how matter behaves on small scales). Black holes have three observable properties: mass, angular momentum (their rotation) and charge (the amount of positive or negative particles they contain). However, in an attempt to understand them better, Physicists like Stephen Hawking applied the laws of thermodynamics to black holes. This along with the idea of Hawking radiation in which a particle and its anti-particle form spontaneously near a black hole and then one of them get sucked in while the other escapes lead Hawking and others to claim that black holes do have a finite temperature which is very, very near zero Kelvin. In general, it is assumed that only things which give off radiation (like the Sun) can have a temperature so Hawking radiation accounts for this. I am sure there are tons of books about black holes at your local bookstore since the public has always been facinated with them. I would suggest starting simple by looking at astronomy text books since the physics can get quite complicated quite quickly. Good luck! [Moderator's note: The Usenet Relativity FAQ has some useful information about black holes and Hawking radiation.]
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