The evaporation of charged black holes

TL;DR

This paper investigates the quantum gravitational effects on the evaporation process of charged black holes, revealing significant deviations from semiclassical predictions and providing a detailed corrected evaporation history.

Contribution

It introduces a quantum gravity-based framework to compute Hawking radiation spectra, including backreaction and metric fluctuations, for near-extremal charged black holes.

Findings

Neutral emission is suppressed near extremality due to large metric fluctuations.

Black holes close to extremality emit entangled photon pairs rather than individual photons.

Semiclassical Schwinger emission rate remains valid despite large geometric changes.

Abstract

Charged particle emission from black holes with sufficiently large charge is exponentially suppressed. As a result, such black holes are driven towards extremality by the emission of neutral Hawking radiation. Eventually, an isolated black hole gets close enough to extremality that the gravitational backreaction of a single Hawking photon becomes important, and the QFT in curved spacetime approximation breaks down. To proceed further, we need to use a quantum theory of gravity. We make use of recent progress in our understanding of the quantum-gravitational thermodynamics of near-extremal black holes to compute the corrected spectrum for both neutral and charged Hawking radiation, including the effects of backreaction, greybody factors, and metric fluctuations. At low temperatures, large fluctuations in a set of light modes of the metric lead to drastic modifications to neutral particle emission that -- in contrast to the semiclassical prediction -- ensure the black hole remains subextremal. Relatedly, angular momentum constraints mean that, close enough to extremality, black holes with zero angular momentum no longer emit individual photons and gravitons; the dominant radiation channel consists of entangled pairs of photons in angular-momentum singlet states. We also compute the effects of backreaction and metric fluctuations on the emission of charged particles. Somewhat surprisingly, we find that the semiclassical Schwinger emission rate is essentially unchanged despite the fact that the emission process leads to large changes in the geometry and thermodynamics of the throat. We present, for the first time, the full history of the evaporation of a large charged black hole. This corrects the semiclassical calculation, which gives completely wrong predictions for almost the entire evaporation history, even for the crudest observables like the temperature seen by a thermometer.