Thermodynamics sheds light on black hole dynamics

TL;DR

This paper explores the connection between black hole thermodynamics and their effective dynamics by using Einstein-Maxwell-dilaton theory to show that black holes can be represented as point particles with conserved entropy.

Contribution

It demonstrates that black hole thermodynamics can be incorporated into effective point-particle descriptions, linking entropy to the scalar-field-dependent mass in a unified framework.

Findings

Black holes satisfy the first law of thermodynamics when reduced to point particles.

The scalar-field-dependent mass of a black hole encodes its entropy.

Global charges and entropy remain constant in the effective description.

Abstract

We propose to unify two a priori distinct aspects of black hole physics : their thermodynamics, and their effective dynamics when they are "skeletonized" as point particles (a useful procedure when tackling, for example, their motion in a coalescing binary system). For that purpose, the Einstein- Maxwell-dilaton (EMD) theory, which contains simple examples of asympotically flat, hairy black hole solutions, will serve as a laboratory. We will find that, when reducing a black hole to a point particle endowed with its specific, scalar-field-sensitive, effective mass, one in fact describes a black hole satisfying the first law of thermodynamics, such that its global charges, and hence its entropy, remain constant. This shows that the integration constant entering the scalar-field dependent mass is its entropy.