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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 collapsed object, usually a [[star]], which has become so [[dense]] that within a certain radius its [[escape velocity]] exceeds the [[speed of light]]. Thus, it absorbs all matter and energy within that radius.  Light and matter can enter, but nothing can ever escape.

'''Black holes''' are theoretical entities which are suggested by the controversial [[theory of relativity]]. They are postulated to be collapsed objects, usually [[stars]], which have become so [[dense]] that within a certain radius their [[escape velocity]] exceeds the [[speed of light]]. Thus, they absorb all matter and energy within that radius.  Light and matter can enter, but nothing can ever escape.

Black holes were first predicted by the [[theory of relativity]].  They have become an increasingly popular topic for magazines, the science page of the [[New York Times]], and science fiction, but whether they really exist remains uncertain.  As with the related theoretical concept of a "[[wormhole]]",<ref>The prediction of the existence of wormholes, and its naming in 1957, predates the prediction and naming (1967) of a black hole.[http://www.nytimes.com/2008/04/14/science/14wheeler.html?pagewanted=print]</ref> it is impossible to prove that no black hole exists anywhere, and thus they fail the [[falsifiability]] requirement of science.   

Black holes have become an increasingly popular topic for magazines, the science page of the [[New York Times]], and science fiction, but whether they really exist remains uncertain.  As with the related theoretical concept of a "[[wormhole]]",<ref>The prediction of the existence of wormholes, and its naming in 1957, predates the prediction and naming (1967) of a black hole.[http://www.nytimes.com/2008/04/14/science/14wheeler.html?pagewanted=print]</ref> it is impossible to prove that no black hole exists anywhere, and thus they fail the [[falsifiability]] requirement of science.