Cosmic Matter Flux May Turn Hawking Radiation Off

TL;DR

This paper argues that matter flux from cosmic backgrounds can suppress Hawking radiation from black holes, implying that black hole evaporation may not occur as previously thought during certain cosmological conditions.

Contribution

It introduces a new perspective on black hole radiation suppression due to cosmic matter flux, challenging standard evaporation models in cosmological contexts.

Findings

Matter flux causes the apparent horizon to become spacelike, preventing Hawking radiation.

Black hole radiation is suppressed when the adiabatic condition is violated by matter influx.

Black hole evaporation may only occur after the cosmic background radiation decays.

Abstract

An astrophysical (cosmological) black hole forming in a cosmological context will be subject to a flux of infalling matter and radiation, which will cause the outer apparent horizon (a marginal trapping surface) to be spacelike \cite{ellisetal14}. As a consequence the radiation emitted close to the apparent horizon no longer arrives at infinity with a diverging redshift. Standard calculations of the emission of Hawking radiation then indicate that no blackbody radiation is emitted to infinity by the black hole in these circumstances, hence there will also then be no black hole evaporation process due to emission of such radiation as long as the matter flux is significant. The essential adiabatic condition (eikonal approximation) for black hole radiation gives a strong limit to the black holes that can emit Hawking radiation. We give the mass range for the black holes that can radiate, according to their cosmological redshift, for the special case of the cosmic blackbody radiation (CBR) influx (which exists everywhere in the universe). At a very late stage of black hole formation when the CBR influx decays away, the black hole horizon becomes first a slowly evolving horizon and then an isolated horizon; at that stage, black hole radiation will start. This study suggests that the primordial black hole evaporation scenario should be revised to take these considerations into account.