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[[Image:Iu8969hu.jpg|right|thumb|300px|Artist's conception of a binary system consisting of a black hole (upper left) and a main sequence star (lower right). The black hole is drawing matter from the star via an ''accretion disk'' (blue) around it, and some of this matter forms a gas jet (also blue).]]
[[Image:Iu8969hu.jpg|right|thumb|300px|Artist's conception of a binary system consisting of a black hole (upper left) and a main sequence star (lower right). The black hole is drawing matter from the star via an ''accretion disk'' (blue) around it, and some of this matter forms a gas jet (also blue).]]
Black holes are increasingly promoted by [[liberal]] publications, such as the science page of the ''[[New York Times]]'', glossy magazines, and the movies the ''Event Horizon'' (1997), ''The Black Hole'' (TV, 2006), and ''Interstellar'' (2014). 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.
Because of [[quantum mechanics|quantum-mechanical]] phenomena involving Hawking Radiation, discussed later in the article, black holes must emit radiation and thus are a logical contradiction at the microscopic level.
Black holes have never been directly observed, and there is no direct evidence for their existence. Even believers in black holes should admit that there are far fewer than predicted by theory, and they lose credibility when they fail to address that undisputed truth. They will cite evidence of observations of radiation from accretion disks, motion of stars near the center of the galaxy, and "gravitational lensing", having all the properties that relativity predicts, around places where there are no visible objects. Like positrons, their existence was predicted (in both cases based on relativity) before there was any actual evidence of their existence.
Black holes are assumed to come into existence from extremely large stars that collapse into a state of high density when they run out of fusion fuel. An object becomes a black hole when it lies entirely inside the Schwarzschild radius (see below) determined by its mass. For most objects, the Schwarzschild radius is very tiny compared with its size (for Earth it is about 1 centimeter), so the object does not lie inside that radius.
Black holes are conceptually associated with "[[wormhole]]s",<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> which never caught on with the public, perhaps due to its poor terminology.
==Mathematical description==
A '''black hole''' is any object that lies entirely inside its own Schwarzschild radius, given by
A '''black hole''' is any object that lies entirely inside its own Schwarzschild radius, given by
:<math>r=\frac{2G}{c^2}\ m</math>
:<math>r=\frac{2G}{c^2}\ m</math>