Black Holes in String Theory

Abstract

A black hole is a region of space time exhibiting such strong gravitational effects that nothing not even particles and electromagnetic radiation such as light can escape from inside it. From the theoretical point of view, black holes provide an intriguing arena in which to explore the challenges posed by the reconciliation of general relativity and quantum mechanics. Since string theory purports to provide a consistent quantum theory of gravity, it should be able to address these challenges. In fact, some of the most fascinating developments in string theory concern quantum-mechanical aspects of black hole physics. These are the subject of this paper. This paper is devoted to trying to find a microscopic quantum description of black holes. One of the most important achievements of string theory in recent times is the construction of examples that provide an affirmative the thermodynamic description of black holes. The thermodynamics of strings is governed largely by the exponential growth of the number of quantum states accessible to a string, as a function of its energy. The behavior of the entropy indicates that at high energies the temperature approaches a finite constant, the Hagedorn temperature. We explain how the counting of string states can be used to give a statistical mechanics derivation of the entropy of black holes. The calculations give results in qualitative agreement with the entropy of Schwarzschild black holes and in quantitative agreement with the entropy of certain charged black holes.