An Etymological Dictionary of Astronomy and Astrophysics

The mathematical expression giving the → entropy, S, of a → black hole as a function of the area of its → event horizon, A: S = (kc³A)/(4Għ), where k is → Boltzmann’s constant, ħ is the → reduced Planck’s constant, and G the → gravitational constant. It can also be expressed by S = (kA)/(4l_P²), where l_P is the → Planck length. The existence of this entropy led to the prediction of the → Hawking radiation, because an entropy is associated with a temperature
and a temperature to a → thermal radiation. The entropy of a black hole increases continuously because the fall of material into it increases its area.

See also: For Jacob D. Bekenstein (1947-), an Israeli theoretical physicist, who contributed to the foundation of black hole thermodynamics; → formula.