Challenging the cosmic censorship in Einstein-Maxwell-scalar theory with numerically simulated gedankenexperiments

TL;DR

This paper uses numerical simulations to test cosmic censorship in Einstein-Maxwell and Einstein-Maxwell-scalar theories, confirming no naked singularities form and exploring scalarization and descalarization effects on black holes.

Contribution

It provides the first comprehensive numerical analysis of cosmic censorship and scalarization phenomena in these theories, including superradiance effects.

Findings

Black holes cannot be overcharged past extremality.

Naked singularities do not form in these theories.

Scalarized black holes can exceed Reissner-Nordström charge bounds.

Abstract

We perform extensive nonlinear numerical simulations of the spherical collapse of (charged) wavepackets onto a charged black hole within Einstein-Maxwell theory and in Einstein-Maxwell-scalar theory featuring nonminimal couplings and a spontaneous scalarization mechanism. We confirm that black holes in full-fledged Einstein-Maxwell theory cannot be overcharged past extremality and no naked singularities form, in agreement with the cosmic censorship conjecture. We show that naked singularities do not form even in Einstein-Maxwell-scalar theory, although it is possible to form scalarized black holes with charge above the Reissner-Nordstr\"om bound. We argue that charge and mass extraction due to superradiance at fully nonlinear level is crucial to bound the charge-to-mass ratio of the final black hole below extremality. We also discuss some "descalarization" mechanisms for scalarized black holes induced either by superradiance or by absorption of an opposite-charged wavepacket; in all cases the final state after descalarization is a subextremal Reissner-Nordstr\"om black hole.