Imaging a non-singular rotating black hole at the center of the Galaxy

TL;DR

This paper explores a non-singular rotating black hole model at the Galactic center, analyzing its properties, potential observational signatures, and implications for distinguishing it from classical Kerr black holes.

Contribution

It introduces a new extension of Hayward's non-singular black hole that avoids singularities and examines its observational signatures, including images and orbital frequencies.

Findings

The extended metric can describe both black holes and naked wormholes.

Images of accretion tori around the object resemble Kerr black hole shadows.

Innermost stable circular orbit frequencies differ from Kerr predictions.

Abstract

We show that the rotating generalization of Hayward's non-singular black hole previously studied in the literature is geodesically incomplete, and that its straightforward extension leads to a singular spacetime. We present another extension, which is devoid of any curvature singularity. The obtained metric depends on three parameters and, depending on their values, yields an event horizon or not. These two regimes, named respectively regular rotating Hayward black hole and naked rotating wormhole, are studied both numerically and analytically. In preparation for the upcoming results of the Event Horizon Telescope, the images of an accretion torus around Sgr A*, the supermassive object at the center of the Galaxy, are computed. These images contain, even in the absence of a horizon, a central faint region which bears a resemblance to the shadow of Kerr black holes and emphasizes the difficulty of claiming the existence of an event horizon from the analysis of strong-field images. The frequencies of the co- and contra-rotating orbits at the innermost stable circular orbit (ISCO) in this geometry are also computed, in the hope that quasi-periodic oscillations may permit to compare this model with Kerr's black hole on observational grounds.