The evaporation of charged black holes

A bstract 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 quantum field theory 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, as well as greybody factors and metric fluctuations. At low temperatures, large fluctuations in a set of quantum-gravitational (almost) zero modes 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 can no longer emit individual photons and gravitons; instead, the dominant radiation channel consists of entangled pairs of photons in angular-momentum singlet states. This causes a sudden slowdown in the evaporation rate by a factor of at least 10 700 . 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. Our results allow us to present, for the first time, the full history of the evaporation of a large charged black hole. A notable feature of this history is that the black hole alternates between exponentially long epochs of integer and half-integer spin that have radically different cooling rates. 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.