What is "black hole of calcutta"

black hole \black" hole`\ 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.

A discipline of unlimited autocracy, upheld by rods, and ferules, and the black hole.
--H. Spencer.

2. (Physics, Astron.) 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.

3. [from the astronomical black hole.] a place into which things may enter, but can never emerge. [Fig., Jocose] "He was so disorganized his office was a black hole."

The Black Hole of Calcutta was a small dungeon in Fort William in Calcutta, India where troops of Siraj ud-Daulah, the Nawab of Bengal, held British prisoners of war after the Bengali army captured the fort on 20 June 1756.

John Zephaniah Holwell, one of the British prisoners and an employee of the East India Company, said that, after the fall of Fort William, the surviving British soldiers and persons, Anglo-Indian soldiers, and Indian civilians were imprisoned overnight in conditions so cramped that many people died from suffocation and heat exhaustion, and that 123 of 146 prisoners of war died.