Thermodynamic light on black holes.
Abstract
Some thermodynamic properties of black holes are discussed. Hawking (1974) showed that the entropy of a black hole is proportional to the surface area of the event horizon, which is the outer boundary of the region from which no light or information can escape. If the entropy of the surrounding area is allowed to rise, the black hole may lose energy and shrink, possibly evaporating away completely in an explosion. The energy radiation does not come from within the black hole but from the region just outside the event horizon  as energy flows away, a compensatory flux of negative energy streams into the black hole. Nonrotating black holes have a negative specific heat, that is, their temperature increases as they lose heat. Highly rotating or charged holes have positive specific heat, which leads to speculation as to the properties of black holes in the vicinity of the sign change of the specific heat. Penrose (1969) suggested a mechanism for extracting energy from a rotating black hole, and some theoretical procedures for achieving energy extraction are considered.
 Publication:

New Scientist
 Pub Date:
 July 1977
 Bibcode:
 1977NewSc..75..238D
 Keywords:

 Black Holes (Astronomy);
 Radiative Heat Transfer;
 Thermodynamic Properties;
 Entropy;
 Relativity;
 Singularity (Mathematics);
 SpaceTime Functions;
 Specific Heat;
 Astrophysics;
 Black Holes:Thermodynamics