Black hole in asymmetric cosmological bounce

TL;DR

This paper analyzes the causal structure of a McVittie spacetime in an asymmetric cosmological bounce, revealing the transient nature of black holes during cosmic contraction and expansion phases.

Contribution

It provides a detailed analysis of trapping horizons and null geodesics in an asymmetric bounce scenario, highlighting the temporary existence of black holes.

Findings

A trapped region exists from the start of contraction until just before the bounce.

Trapping horizons disappear at the minimum scale, exposing a naked singularity.

Black holes cannot persist throughout both contracting and expanding phases.

Abstract

We determine the causal structure of the McVittie spacetime for a cosmological model with an asymmetric bounce. The analysis includes the computation of trapping horizons, regular, trapped, and anti-trapped regions, and the integration of the trajectories of radial null geodesics before, during, and after the bounce. We find a trapped region since the beginning of the contracting phase up to shortly before the bounce, thus showing the existence of a black hole. When the universe reaches a certain minimum scale in the contracting phase, the trapping horizons disappear and the central singularity becomes naked. These results suggest that neither a contracting nor an expanding universe can accommodate a black hole at all times.