Mass Inflation in Brans-Dicke gravity

TL;DR

This paper investigates the internal structure of charged black holes in Brans-Dicke gravity, demonstrating that mass inflation occurs and stabilizes scalar variations, through both analytical and numerical methods.

Contribution

It provides the first detailed non-linear analysis of mass inflation in Brans-Dicke gravity using adaptive mesh refinement simulations.

Findings

Mass inflation occurs inside charged black holes in Brans-Dicke gravity.

Scalar field variations are suppressed during mass inflation.

Numerical results confirm homogeneous approximation predictions.

Abstract

A detailed non-linear analysis of the internal structure of spherical, charged black holes that are accreting scalar matter is performed in the framework of the Brans-Dicke theory of gravity. We choose the lowest value of the Brans-Dicke parameter that is compatible with observational constraints. First, the homogeneous approximation is used. It indicates that mass inflation occurs and that the variations of the Brans-Dicke scalar inside the black hole, which could in principle be large in the absence of mass inflation, become small when mass inflation does occur. Then, a full non-linear numerical study of the black hole interior perturbed by a self-gravitating massless uncharged scalar-field is performed. We use an algorithm with adaptive mesh refinement capabilities. In this way, the changes in the internal structure of the black hole caused by mass inflation are determined, as well as the induced variations of the Brans-Dicke scalar, confirming, qualitatively, the indications given by the homogeneous approximation.