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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 theoretical mass with an [[escape velocity]] greater than the speed of light.  They cannot be observed directly, but several have been identified via indirect observation<ref>http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/971124b.html</ref> <ref>http://dsc.discovery.com/news/2008/04/01/smallest-black-hole.html</ref>.  While matter and energy, even light, may not escape a black hole, [[Stephen Hawking]] has shown that they should emit [[Hawking radiation]], which absent of an influx of mass-energy would lead to the evaporation of the black hole. This theory however is unable to be tested.

A '''black hole''' is a theoretical mass with an [[escape velocity]] greater than the speed of light.  They cannot be observed directly. Several have been identified by [[Big Science]] via indirect observation<ref>http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/971124b.html</ref> <ref>http://dsc.discovery.com/news/2008/04/01/smallest-black-hole.html</ref>.  While matter and energy, even light, may not escape a black hole, [[Stephen Hawking]] has shown that they should emit [[Hawking radiation]], which absent of an influx of mass-energy would lead to the evaporation of the black hole. This theory however is unable to be tested.

The outer surface of a black hole is an [[event horizon]], a non-material dimensional boundary, beyond which nothing can escape.

The outer surface of a black hole would be an [[event horizon]], a non-material dimensional boundary, beyond which nothing can escape.

Black holes are thought to form when supermassive stars more than ten times the mass of the Sun run out of hydrogen fuel and die.  When this happens, the iron core at the center of the star implodes under its own gravity in a supernova.  The outer layers of the star are blasted into space in one of the most energetic events in the universe.  Not all supernovae result in black holes though.  If the mass of the core is large enough, [[Chandrasekhar limit|about 1.2 times the mass of the Sun]], the leftover gravity of the shrinking core stalls the outward rush of the initial blast, and crushes the core into a point of infinite gravity: a black hole.  This rare event is known as a hypernova and is even more energetic than a supernova.

Black holes are thought to form when supermassive stars more than ten times the mass of the Sun run out of hydrogen fuel and die.  When this happens, the iron core at the center of the star implodes under its own gravity in a supernova.  The outer layers of the star are blasted into space in one of the most energetic events in the universe.  Not all supernovae result in black holes though.  If the mass of the core is large enough, [[Chandrasekhar limit|about 1.2 times the mass of the Sun]], the leftover gravity of the shrinking core stalls the outward rush of the initial blast, and crushes the core into a point of infinite gravity: a black hole.  This rare event is known as a hypernova and is even more energetic than a supernova.