| Astronomy. a theoretical massive object, formed at the beginning of the universe or by the gravitational collapse of a star exploding as a supernova, whose gravitational field is so intense that no electromagnetic radiation can escape. |
| 1. | Also called Black Hole of Cal⋅cut⋅ta. a small prison cell in Fort William, Calcutta, in which, in 1756, Indians are said to have imprisoned 146 Europeans, only 23 of whom were alive the following morning. |
| 2. | (lowercase ) any usually wretched place of imprisonment or confinement. |
| black hole n.
|
In astronomy, an object so massive that nothing, not even light, can escape its gravitation. Black holes were given their name because they absorb all the light that falls on them. The existence of black holes was first predicted by the general theory of relativity. Supermassive black holes have been found in the centers of many galaxies. Stellar black holes are thought to arise from the death of very massive stars. Astronomers expect to find many stellar black holes in the Milky Way.
Note: Figuratively, the term black hole is used to refer to a total disappearance: “They never saw the man again — he might as well have fallen into a black hole.”
black hole
1. An expression which depends on its own value or a technique to detect such expressions. In graph reduction, when the reduction of an expression is begun, the root of the expression can be overwritten with a black hole. If the expression depends on its own value, e.g.
x = x + 1
then it will try to evaluate the black hole which will usually print an error message and abort the program. A secondary effect is that, once the root of the expression has been black-holed, parts of the expression which are no longer required may be freed for garbage collection.
Without black holes the usual result of attempting to evaluate an expression which depends on itself would be a stack overflow. If the expression is evaluated successfully then the black hole will be updated with the value.
Expressions such as
ones = 1 : ones
are not black holes because the list constructor, : is lazy so the reference to ones is not evaluated when evaluating ones to WHNF.
2. Where an electronic mail message or news aritcle has gone if it disappears mysteriously between its origin and destination sites without returning a bounce message. Compare bit bucket.
[The Jargon File]
black hole
A wretched prison cell or other place of confinement. For example, The punishment is solitary confinement, known as the black hole. This term acquired its meaning in 1756 with the event known as the Black Hole of Calcutta. On the night of June 20, the ruler of Bengal confined 146 Europeans in a prison space of only 14 by 18 feet. By morning all but 23 of them had suffocated to death. Although historians since have questioned the truth of the story, it survives in this usage.
A great void or abyss. For example, Running a single small newspaper ad to launch a major campaign is useless; it amounts to throwing our money into a black hole. This usage alludes to a region, so named by astronomers, whose gravitational field is so intense that no electromagnetic radiation can escape from it. [Late 1970s]