Inside charged black holes II. Baryons plus dark matter

TL;DR

This paper investigates the interior structure of self-similar charged black holes accreting baryons and dark matter, revealing how relativistic streaming induces mass inflation and affects singularity formation.

Contribution

It extends previous models by including dark matter accretion, analyzing its impact on mass inflation and the nature of singularities inside charged black holes.

Findings

Mass inflation occurs due to relativistic streaming between baryons and dark matter.

The presence of dark matter influences the extent and nature of mass inflation.

Under certain conditions, the baryonic fluid can pass through the Cauchy horizon without forming a null singularity.

Abstract

(Abridged) This is the second of two companion papers on the interior structure of self-similar accreting charged black holes. In the first paper, the black hole was allowed to accrete only a single fluid of charged baryons. In this second paper, the black hole is allowed to accrete in addition a neutral fluid of almost non-interacting dark matter. Relativistic streaming between outgoing baryons and ingoing dark matter leads to mass inflation near the inner horizon. When enough dark matter has been accreted that the center of mass frame near the inner horizon is ingoing, then mass inflation ceases and the fluid collapses to a central singularity. A null singularity does not form on the Cauchy horizon. Although the simultaneous presence of ingoing and outgoing fluids near the inner horizon is essential to mass inflation, reducing one or other of the ingoing dark matter or outgoing baryonic streams to a trace relative to the other stream makes mass inflation more extreme, not the other way round as one might naively have expected. Consequently, if the dark matter has a finite cross-section for being absorbed into the baryonic fluid, then the reduction of the amount of ingoing dark matter merely makes inflation more extreme, the interior mass exponentiating more rapidly and to a larger value before mass inflation ceases. However, if the dark matter absorption cross-section is effectively infinite at high collision energy, so that the ingoing dark matter stream disappears completely, then the outgoing baryonic fluid can drop through the Cauchy horizon. In all cases, the solutions do not depend on what happens in the infinite past or future. We discuss in some detail the physical mechanism that drives mass inflation.