What is Black Hole?

A black hole is an object with a gravitational field so powerful that a region of space becomes cut off from the rest of the universe – no matter or radiation, including visible light, that has entered the region can ever escape. The lack of escaping electromagnetic radiation renders the inside of black holes (beyond the event horizon) invisible, hence the name. However, black holes can be detectable if they interact with matter, e.g. by sucking in gas from an orbiting star. The gas spirals inward, heating up to very high temperatures and emitting large amounts of light, X-rays and Gamma rays in the process while still outside of the event horizon.[1][2][3] Black holes are also thought to emit a weak form of thermal energy called Hawking radiation.[4][5][6]

2007-06-08 11:47:18 補充：
A black hole is a region of spacetime from which nothing can escape, even light. http://www.damtp.cam.ac.uk/user/gr/public/bh_intro.html

n physics, Hawking radiation is thermal radiation thought to be emitted by black holes due to quantum effects. It is named after British physicist Stephen Hawking who worked out the theoretical argument for its existence in 1974. Hawking's discovery became the first convincing insight into quantum gravity. However, the existence of Hawking radiation remains controversial.


Black holes are sites of immense gravitational attraction into which surrounding matter is drawn by gravitational forces. Classically, the gravitation is so powerful that nothing, not even radiation, can escape from the black hole. However, by doing a calculation in the framework of quantum field theory in curved spacetimes, Hawking showed quantum effects allow black holes to emit radiation in a thermal spectrum.

Physical insight on the process may be gained by imagining that particle antiparticle radiation is emitted from just beyond the event horizon. This radiation does not come directly from the black hole itself, but rather is a result of virtual particles being "boosted" by the black hole's gravitation into becoming real particles.

A more precise, but still much simplified view of the process is that vacuum fluctuations cause a particle-antiparticle pair to appear close to the event horizon of a black hole. One of the pair falls into the black hole whilst the other escapes. In order to fill the energy 'hole' left by the pair's spontaneous creation, energy tunnels out of the black hole and across the event horizon. By this process the black hole loses mass, and to an outside observer it would appear that the black hole has just emitted a particle.


Black hole evaporation
When particles escape, the black hole loses a small amount of its energy and therefore of its mass (recall that mass and energy are related by Einstein's famous equation E = mc²).

2007-06-08 11:46:57 補充：
http://en.wikipedia.org/wiki/Black_holes