Entropy of extremal black holes

TL;DR

This paper reviews black hole thermodynamics, introduces a microscopic model supporting the Bekenstein-Hawking entropy for extremal black holes, and discusses how topology summation reconciles semiclassical discontinuities.

Contribution

It presents a microscopic model that confirms the Bekenstein-Hawking entropy formula applies to extremal black holes, resolving previous semiclassical discontinuity issues.

Findings

Bekenstein-Hawking formula holds for extremal black holes

Summing over topologies reconciles semiclassical discontinuities

Microscopic model supports thermodynamic consistency

Abstract

After summarizing the development of black hole thermodynamics in the seventies, we describe a recent microscopic model. This model suggests that the Bekenstein-Hawking area formula holds for extremal black holes as well as for ordinary (non-extremal) ones. On the other hand, semiclassical studies have suggested a discontinuity between non-extremal and extremal cases. We indicate how a reconciliation has been brought about by summing over topologies.