A dungeon or dark cell in a prison; a military lock-up or guardroom; -- now commonly with allusion to the cell (the Black Hole) in a fort at Calcutta (called the Black Hole of Calcutta), into which 146 English prisoners were thrust by the nabob Suraja Dowla on the night of June 20, 1765, and in which 123 of the prisoners died before morning from lack of air.
An astronomical object whose mass is so condensed that the gravitational force does not allow anything, even light, to escape from its outer limit (the event horizon). The existence of such objects was first proposed from theoretical considerations. Because light cannot escape from such objects, they have not yet been detected with certainty (1998), but several "candidates" have been observed whose properties strongly suggest that they are black holes. Some theorists suggest that the centers of many galaxies may have large black holes at their cores. See also escape velocity.
A region of space where the density of matter is so great, and the pull of gravity so strong, that not even light can escape. Black holes are thought to be the end point in the evolution of some stars. Massive black holes may be located at the centers of some active galaxies.