Dynamical black hole in a bouncing universe

TL;DR

This paper investigates the evolution of black holes within a bouncing universe model, revealing that black holes form and disappear dynamically around the bounce, challenging the notion of their eternal existence in such cosmologies.

Contribution

It provides a detailed analysis of the causal structure and trapping horizons in a bouncing universe, showing the transient nature of black holes during cosmic evolution.

Findings

Dynamical black holes exist only during certain phases of the bounce.

Black holes disappear at the minimum scale of the universe.

Post-bounce, the central singularity becomes naked.

Abstract

We analyze the causal structure of McVittie spacetime for a classical bouncing cosmological model. In particular, we compute the trapping horizons of the metric and integrate the trajectories of radial null geodesics before, during, and after the bounce takes place. In the contracting phase up to the occurrence of the bounce, a dynamical black hole is present. When the universe reaches a certain minimum scale, the trapping horizons disappear and the black hole ceases to exist. After the bounce, the central weak singularity becomes naked. In the expanding phase, for large positive values of the cosmic time, the behaviour of null geodesics indicates that the solution contains a black hole. These results suggest that neither a contracting nor an expanding universe can accommodate a black hole at all times.