Semiclassical environment of collapsing shells

TL;DR

This paper analyzes the semiclassical radiation environment of collapsing shells, both forming and not forming horizons, revealing complex flux behaviors and potential implications for black hole thermodynamics and entropy.

Contribution

It provides detailed calculations of semiclassical fluxes for various observer positions around collapsing shells, including non-horizon forming cases, advancing understanding of black hole thermodynamics.

Findings

Observers detect nontrivial flux patterns during collapse.

Shells not forming horizons emit a pulse of radiation that becomes thermalized.

Results suggest implications for black hole entropy and backreaction effects.

Abstract

We explore in detail the semiclassical environment of collapsing shells of matter, and determine the semiclassical flux measured by a variety of observers. This study is a preliminary step in a broader investigation of thermodynamic properties of the geometry of collapsing objects. Specifically, in this paper we consider spherically symmetric null and timelike collapsing shells which form an event horizon, and calculate the flux measured by observers both inside and outside the shell, and both inside and outside the event horizon, and find nontrivial results in most of the cases. Additionally, we also investigate the environment of a shell which collapses but \emph{does not} form a horizon, halting at some radius larger than the Schwarzschild radius, and find that such an object generically gives rise to a pulse of radiation which is sharply peaked as it travels inwards and is reflected at the origin, and eventually emerges from the shell in a "thermalized" form. Our results have potential consequences in addressing questions pertaining, e.g. to black hole entropy and backreaction.