<span class="SFPTagline"> From SCIFIPEDIA </span>

A black hole is a concept predicted by Einstein's General Theory of Relativity, describing a region of space where the gravitational force cannot be countered. A black hole is surrounded by an event horizon, a region through which neither light nor any other form of information can pass; hence, the interior of a black hole can never be seen from the outside, and any traveller who passes through the event horizon can neither escape nor pass along information about what is inside.

The word "black hole" was coined by John Archibald Wheeler. Earlier words for the concept included the Russian term "frozen star" or the astrophysical term "collapsar," short for collapsed star.

A closely related term is singularity, the point where the equations describing gravitation and the curvature of space-time reach infinity. A singularity is hypothesized to exist at the center of a black hole. (Note that the words singularity and black hole are not interchangeable; a singularity lies inside the black hole]. Any spaceship crossing the event horizon of a (nonrotating) black hole must inevitably be drawn to the infinitely dense singularity at the center. The nature and behavior of the phenomena associated with the singularity vary greatly from story to story.

In principle, a black hole would be invisible, since light cannot escape. Such a black hole could be detected by the bending of starlight light around it by the intense gravitational fields. In the real world, however, space is not completely empty, and black holes are often surrounded by a brightly glowing accretion disk of dust and gas orbiting and being swallowed by the black hole.

Stories may focus on the gravitational aspects of a black hole (see Larry Niven's short story "The Hole Man" in A Hole in Space or the use of a black hole for space travel beyond the reach of sub-light speeds (see Joe Haldeman's The Forever War. Associated fictional devices are wormholes in space-time, which may or may not be attributable to the presence of a singularity in the story.

Time travel in some way connected with the distortion of space-time near a black hole is another fictional device seen in genre literature. Sometimes undesired time travel as predicted by special relativity is a theme (as in Niven's World Out of Time about a corpsicle revived and sent on a ramjet mission, who returns to an Earth even more distant in time).

Sometimes a black hole may be employed as a power source, such as in the short story "Killing Vector" in Charles Sheffield's collection The MacAndrew Chronicles. The very real dangers of using such a powerful object as a power source is one of the points used to underscore the environmental themes in David Brin's novel Earth.

Unusually intense gravitational phenomena that do not necessarily approach the rapacious power of black holes nonetheless make for some very interesting storytelling in hard science fiction ("hard sf"). Particularly good examples of this include Niven's eponymous short story in Neutron Star and Hal Clement's novel Mission of Gravity.