Pre-Hawking radiation may allow for reconstruction of the mass distribution of the collapsing object

TL;DR

This paper suggests that pre-Hawking radiation emitted during gravitational collapse contains information about the initial mass distribution of the collapsing object, challenging the notion that only total mass is encoded in black hole radiation.

Contribution

It demonstrates that the flux of pre-Hawking radiation varies with the mass distribution during collapse, enabling potential reconstruction of the initial mass profile.

Findings

Flux differs between single and concentric shell collapses

Fluxes become indistinguishable after black hole formation

Initial mass distribution influences pre-Hawking radiation

Abstract

Hawking radiation explicitly depends only on the black hole's total mass, charge and angular momentum. It is therefore generally believed that one cannot reconstruct the information about the initial mass distribution of an object that made the black hole. However, instead of looking at radiation from a static black hole, we can study the whole time-dependent process of the gravitational collapse, and pre-Hawking radiation which is excited because of the time-dependent metric. We compare radiation emitted by a single collapsing shell with that emitted by two concentric shells of the equivalent total mass. We calculate the gravitational trajectory and the momentum energy tensor. We show that the flux of energy emitted during the collapse by a single shell is significantly different from the flux emitted by two concentric shells of the equivalent total mass. When the static black hole is formed, the fluxes become indistinguishable. This implies that an observer studying the flux of particles from a collapsing object could in principle reconstruct information not only about the total mass of the collapsing object, but also about the mass distribution.