Black hole formation from a null fluid in extended Palatini gravity

TL;DR

This paper derives an exact analytical solution describing black hole formation from null matter flux in an extended Palatini gravity theory, revealing a Reissner-Nordstrom-like spacetime with an unconventional charge term.

Contribution

It provides the first exact solution for black hole formation in Palatini quadratic gravity, extending Vaidya solutions and analyzing the effects of null fluxes on black hole spacetimes.

Findings

Black hole formation modeled by null fluxes in Palatini gravity.

Resulting spacetime resembles Reissner-Nordstrom with an effective, sign-inverted charge.

The solution reduces to Schwarzschild when flux vanishes.

Abstract

We study the formation and perturbation of black holes by null fluxes of neutral matter in a quadratic extension of General Relativity formulated a la Palatini. Working in a spherically symmetric space-time, we obtain an exact analytical solution for the metric that extends the usual Vaidya-type solution to this type of theories. We find that the resulting space-time is formally that of a Reissner-Nordstrom black hole but with an effective charge term carrying the wrong sign in front of it. This effective charge is directly related to the luminosity function of the radiation stream. When the ingoing flux vanishes, the charge term disappears and the space-time relaxes to that of a Schwarzschild black hole. We provide two examples that illustrate the formation of a black hole from Minkowski space and the perturbation by a finite pulse of radiation of an existing Schwarzschild black hole.