Black hole interiors in the thermal view of scalar-tensor gravity

TL;DR

This paper extends the thermal analogy of scalar-tensor gravity to black hole interiors, revealing how the singularity exhibits 'hot' behavior and diverges from Einstein gravity, influenced by surrounding matter content.

Contribution

It introduces a thermal perspective to black hole interiors in scalar-tensor gravity and explores how matter affects the approach to Einstein gravity near singularities.

Findings

Black hole singularities are 'hot' and diverge from Einstein gravity.

The thermal analogy applies to interior regions near singularities.

Matter content influences the approach to Einstein gravity.

Abstract

The thermal view of scalar-tensor gravity is an analogy with a dissipative fluid. The scalar degree of freedom excites gravity to a positive ``temperature'', while Einstein gravity is the ``zero-temperature'' equilibrium state. We extend this thermal analogy to the interior region near the singularity of spherical, vacuum, uncharged black holes by using the universality of the Kasner behaviour near spacelike singularities. The singularity is ``hot'', meaning that gravity diverges from general relativity. The discussion is then extended to black holes in the presence of perfect or imperfect fluids with constant equation of state -- the latter determines whether Einstein gravity is approached or not.