Regular black holes as an alternative to black bounce

Abstract

The so-called black bounce mechanism of singularity suppression, proposed by Simpson and Visser, consists in replacing the spherical radius $r$ in the metric tensor with $\sqrt{r^2 + a^2}$, $a = \rm const >0$. This removes a singularity at $r=0$ and its neighborhood from space-time, and there emerges a regular minimum of the spherical radius that can be a wormhole throat or a regular bounce (if located inside a black hole). Instead, it is proposed here to make $r=0$ a regular center by proper (Bardeen type) replacements in the metric, preserving its form at large $r$. Such replacements are applied to a class of metrics satisfying the condition $R^t_t = R^r_r$ for their Ricci tensor, in particular, to the Schwarzschild, Reissner-Nordström and Einstein-Born-Infeld solutions. A simpler version of nonlinear electrodynamics (NED) is proposed, for which a black hole solution is similar to the Einstein-Born-Infeld one but is simpler expressed analytically. All new regular metrics can be presented as solutions to NED-Einstein equations with radial magnetic fields.