On the viability of regular black holes

TL;DR

This paper critically examines regular black hole models, revealing their instabilities and limitations in describing black hole evaporation, especially near the end stages, and discusses potential ways to address these issues.

Contribution

It identifies fundamental instabilities in existing regular black hole models and argues that these models cannot fully describe the evaporation process without losing predictive power.

Findings

Regular black hole cores are exponentially unstable.

Evaporation time is infinite, conflicting with stability timescales.

Models cannot be fully predictive of final evaporation stages.

Abstract

The evaporation of black holes raises a number of conceptual issues, most of them related to the final stages of evaporation, where the interplay between the central singularity and Hawking radiation cannot be ignored. Regular models of black holes replace the central singularity with a nonsingular spacetime region, in which an effective classical geometric description is available. It has been argued that these models provide an effective, but complete, description of the evaporation of black holes at all times up to their eventual disappearance. However, here we point out that known models fail to be self-consistent: the regular core is exponentially unstable against perturbations with a finite timescale, while the evaporation time is infinite, therefore making the instability impossible to prevent. We also discuss how to overcome these difficulties, highlighting that this can be done only at the price of accepting that these models cannot be fully predictive regarding the final stages of evaporation.