Role of evaporation in gravitational collapse

TL;DR

This paper explores how quantum effects during gravitational collapse prevent horizon crossing, leading to a scenario where collapsing matter remains just outside the horizon and experiences high-energy phenomena.

Contribution

It introduces a modified collapse model incorporating evaporation effects, showing matter never crosses the horizon and encounters firewall-like conditions.

Findings

Collapse accelerates due to evaporation but does not cross the horizon.

Collapsing matter remains at a sub-Planckian distance from the horizon.

Observers detect firewall-like energy densities and fluxes.

Abstract

We investigate the possibility that quantum effects responsible for black hole radiation do not allow for hori- zon crossing of gravitationally collapsing matter in a finite time as seen by distant observers. We consider this in the context of the collapse of evaporating massive thin dust shells using two families of metrics to describe the exterior geometry: the outgoing Vaidya metric and the retarded Schwarzschild metric. We describe how this hypothesis results in a modified equation of motion for the shell. In each case the collapse is accelerated due to evaporation, but the Schwarzschild radius is not crossed. Instead the shell is always at a certain sub-Planckian distance from this would-be horizon that depends only on the mass and evaporation rate, while a comoving observer encounters firewall-like energy density and flux with a natural cutoff.