The causal structure of dynamical charged black holes

TL;DR

This paper investigates the causal structure of dynamical charged black holes through numerical simulations, revealing how inner horizons evolve with Hawking radiation and potential implications for cosmic censorship and black hole complementarity.

Contribution

The study provides new insights into the evolution of inner horizons in charged black holes, especially under Hawking radiation and large numbers of scalar fields, challenging existing notions of singularity and cosmic censorship.

Findings

Inner horizon is a null Cauchy horizon without Hawking radiation.

Hawking radiation makes the inner horizon space-like and separates it from the Cauchy horizon.

Large number of scalar fields can extend results beyond the inner horizon, potentially violating cosmic censorship.

Abstract

We study the causal structure of dynamical charged black holes, with a sufficient number of massless fields, using numerical simulations. Neglecting Hawking radiation, the inner horizon is a null Cauchy horizon and a curvature singularity due to mass inflation. When we include Hawking radiation, the inner horizon becomes space-like and is separated from the Cauchy horizon, which is parallel to the out-going null direction. Since a charged black hole must eventually transit to a neutral black hole, we studied the neutralization of the black hole and observed that the inner horizon evolves into a space-like singularity, generating a Cauchy horizon which is parallel to the in-going null direction. Since the mass function is finite around the inner horizon, the inner horizon is regular and penetrable in a general relativistic sense. However, since the curvature functions become trans-Planckian, we cannot saymore about the region beyond the inner horizon, and it is natural to say that there is a 'physical' space-like singularity. However, if we assume an exponentially large number of massless scalar fields, our results can be extended beyond the inner horizon. In this case, strong cosmic censorship and black hole complementarity can be violated.