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[[Image:Iu8969hu.jpg|right|thumb|300px|Artist's conception of a binary system consisting of a black hole and a main sequence star.  The black hole is drawing matter from the main sequence star via an accretion disk around it, and some of this matter forms a gas jet.]]

[[Image:Iu8969hu.jpg|right|thumb|300px|Artist's conception of a binary system consisting of a black hole and a main sequence star.  The black hole is drawing matter from the main sequence star via an [[accretion disk]] around it, and some of this matter forms a gas jet.]]

A '''black hole''' is a mass with an [[escape velocity]] greater than the speed of light. While matter and energy, even light, may not escape a black hole, [[Stephen Hawking]] has shown that they should emit [[Hawking radiation]], which absent an influx of mass-energy would lead to the evaporation of the black hole.  The outer surface of a black hole is an [[event horizon]], a non-material dimensional boundary, beyond which nothing can escape.

A '''black hole''' is a mass with an [[escape velocity]] greater than the speed of light. While matter and energy, even light, may not escape a black hole, [[Stephen Hawking]] has shown that they should emit [[Hawking radiation]], which absent an influx of mass-energy would lead to the evaporation of the black hole.  The outer surface of a black hole is an [[event horizon]], a non-material dimensional boundary, beyond which nothing can escape.