Naked and Thunderbolt Singularities in Black Hole Evaporation

TL;DR

This paper explores the end stages of black hole evaporation, suggesting that semi classical models predict singularities called thunderbolts, which imply a breakdown of classical theory and the need for full quantum descriptions.

Contribution

It compares different semi classical models, showing that more general equations predict thunderbolts, indicating a breakdown of semi classical approximation at black hole evaporation's end.

Findings

Semi classical models with extra symmetry predict naked singularities.

More general semi classical equations predict thunderbolts.

Thunderbolts imply the breakdown of semi classical approximation.

Abstract

If an evaporating black hole does not settle down to a non radiating remnant, a description by a semi classical Lorentz metric must contain either a naked singularity or what we call a thunderbolt, a singularity that spreads out to infinity on a spacelike or null path. We investigate this question in the context of various two dimensional models that have been proposed. We find that if the semi classical equations have an extra symmetry that make them solvable in closed form, they seem to predict naked singularities but numerical calculations indicate that more general semi classical equations, such as the original CGHS ones give rise to thunderbolts. We therefore expect that the semi classical approximation in four dimensions will lead to thunderbolts. We interpret the prediction of thunderbolts as indicating that the semi classical approximation breaks down at the end point of black hole evaporation, and we would expect that a full quantum treatment would replace the thunderbolt with a burst of high energy particles. The energy in such a burst would be too small to account for the observed gamma ray bursts.