Inside an Asymptotically Flat Hairy Black Hole

TL;DR

This paper investigates the interior structure of charged, asymptotically flat black holes with scalar hair, revealing complex interior dynamics and arguing against the existence of Cauchy horizons in such configurations.

Contribution

It introduces a new family of black hole solutions with scalar hair and analyzes their interior, including oscillatory behavior and singularity structure, with a general argument against Cauchy horizons.

Findings

Interior resembles holographic superconductor

Scalar field exhibits Josephson oscillations

Final singularity depends on black hole parameters

Abstract

We study the interior of a recently constructed family of asymptotically flat, charged black holes that develop (charged) scalar hair as one increases their charge at fixed mass. Inside the horizon, these black holes resemble the interior of a holographic superconductor. There are analogs of the Josephson oscillations of the scalar field, and the final Kasner singularity depends very sensitively on the black hole parameters near the onset of the instability. In an Appendix, we give a general argument that Cauchy horizons cannot exist in a large class of stationary black holes with scalar hair.