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According to the general theory of [[relativity]], a '''black hole''' is a region of [[space]] from which nothing, including [[light]], can escape. It is the result of the deformation of [[spacetime]] caused by a very compact [[mass]]. Around a black hole there is an undetectable [[surface]] which marks the point of no return, called an [http://en.wikipedia.org/wiki/Event_horizon event horizon]. It is called "black" because it absorbs all the [[light]] that hits it, [[reflecting]] nothing, just like a perfect black [[body]] in [http://en.wikipedia.org/wiki/Thermodynamics thermodynamics]. Under the [[theory]] of [[quantum mechanics]] black holes [[possess]] a [[temperature]] and emit [http://en.wikipedia.org/wiki/Hawking_radiation Hawking radiation].
Despite its [[invisible]] interior, a black hole can be [[observed]] through its [[interaction]] with other [[matter]]. A black hole can be [[inferred]] by tracking the [[Motion|movement]] of a [[group]] of [[stars]] that [[orbit]] a region in [[space]]. Alternatively, when [[gas]] falls into a [http://en.wikipedia.org/wiki/Stellar_black_hole stellar black hole] from a [http://en.wikipedia.org/wiki/Binary_star companion star], the [[gas]] [[spiral]]s inward, heating to very high [[temperatures]] and emitting large amounts of [[radiation]] that can be detected from earthbound and [[Earth]]-orbiting [http://en.wikipedia.org/wiki/Telescope telescopes].
[[Astronomers]] have identified numerous stellar black hole [[candidates]], and have also found [[evidence]] of [http://en.wikipedia.org/wiki/Supermassive_black_hole supermassive black holes] at the [[center]] of [[galaxies]]. After [[observing]] the [[motion]] of nearby stars for 16 years, in 2008 astronomers found compelling [[evidence]] that a [http://en.wikipedia.org/wiki/Supermassive_black_hole supermassive black hole] of more than 4 million solar masses is located near the [http://en.wikipedia.org/wiki/Sagittarius_A* Sagittarius A*] region in the center of the [[Milky Way]] [[galaxy]].[http://en.wikipedia.org/wiki/Black_hole]
[[Category: Astronomy]]
According to the general theory of [[relativity]], a '''black hole''' is a region of [[space]] from which nothing, including [[light]], can escape. It is the result of the deformation of [[spacetime]] caused by a very compact [[mass]]. Around a black hole there is an undetectable [[surface]] which marks the point of no return, called an [http://en.wikipedia.org/wiki/Event_horizon event horizon]. It is called "black" because it absorbs all the [[light]] that hits it, [[reflecting]] nothing, just like a perfect black [[body]] in [http://en.wikipedia.org/wiki/Thermodynamics thermodynamics]. Under the [[theory]] of [[quantum mechanics]] black holes [[possess]] a [[temperature]] and emit [http://en.wikipedia.org/wiki/Hawking_radiation Hawking radiation].
Despite its [[invisible]] interior, a black hole can be [[observed]] through its [[interaction]] with other [[matter]]. A black hole can be [[inferred]] by tracking the [[Motion|movement]] of a [[group]] of [[stars]] that [[orbit]] a region in [[space]]. Alternatively, when [[gas]] falls into a [http://en.wikipedia.org/wiki/Stellar_black_hole stellar black hole] from a [http://en.wikipedia.org/wiki/Binary_star companion star], the [[gas]] [[spiral]]s inward, heating to very high [[temperatures]] and emitting large amounts of [[radiation]] that can be detected from earthbound and [[Earth]]-orbiting [http://en.wikipedia.org/wiki/Telescope telescopes].
[[Astronomers]] have identified numerous stellar black hole [[candidates]], and have also found [[evidence]] of [http://en.wikipedia.org/wiki/Supermassive_black_hole supermassive black holes] at the [[center]] of [[galaxies]]. After [[observing]] the [[motion]] of nearby stars for 16 years, in 2008 astronomers found compelling [[evidence]] that a [http://en.wikipedia.org/wiki/Supermassive_black_hole supermassive black hole] of more than 4 million solar masses is located near the [http://en.wikipedia.org/wiki/Sagittarius_A* Sagittarius A*] region in the center of the [[Milky Way]] [[galaxy]].[http://en.wikipedia.org/wiki/Black_hole]
[[Category: Astronomy]]
