Black holes, sometimes called "collapsars," are a class of astronomical object which has attracted great attention both from astrophysicists and the general public in the past two decades. According to theory, if an astronomical body is large or dense enough, its gravitational escape velocity will exceed the velocity of light: thus no radiation from it can escape to the outside Universe. It disappears within an "event horizon." Such an object, from which not even light can escape, would seem to be undetectable, yet black holes are of great interest to astronomers and physicists. A number of indirect methods of detecting black holes have been proposed, and indeed a number of black hole "candidates" have been identified. However, black holes remain a theoretical construct, since no persuasive indirect observational evidence has been found that would rule out alternative explanations for these "candidate" objects (1: 321-23). In the body of this study, the conditions under which black holes could form will be outlined, possible classes of black holes surveyed, and the current state of observation reviewed.
The general concept behind black holes is a surprisingly old one. In 1796, the French mathematician Pierre Simon, better known as the Marquis de Laplace, applied Newton's theory of gravitation to the problem of light, which was already known to have a finite velocity. Laplace argued that if a star were large enough, or dense enough, to have a surface escape velocity greater than the velocity of light, its light would be trapped, and it would be undetectable by any telescope (4: 65). However, Laplace's idea was ignored and forgotten. It seemed to have no practical application to astronomical research. The nature and composition of stars were still unknown, and no stellar distance had yet been measured.
By the early twentieth century, the scope of both physics and astronomy had vastly expanded. Shortly before his death ...