What is Black Hole?

A black hole is an object with a gravitational field so powerful that a region of space bees 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 electromagic 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 补充： A black hole is a region of spacetime from which nothing can escape
even light. damtp.cam.ac.uk/user/gr/public/bh_intro
参考: en. *** /wiki/Black_holes
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 e directly from the black hole itself
but rather is a result of virtual particles being "boosted" by the black hole's gravitation into being 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 *** all 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 补充： en. *** /wiki/Black_holes
参考: .knowledge.yahoo/question/?qid=7006072203168