Shapes of rotating nonsingular black hole shadows

TL;DR

This paper investigates how the shadow shapes of nonsingular black holes, characterized by mass, spin, and deviation parameters, differ from Kerr black holes, revealing that the deviation parameter influences shadow size and distortion.

Contribution

It introduces a model of nonsingular black holes extending Kerr black holes and analyzes how the deviation parameter affects their shadow shapes and ergoregions.

Findings

Shadow size decreases with increasing deviation parameter k.

Shadow distortion increases as k increases.

Ergoregion structure is altered by the deviation parameter.

Abstract

It is believed that curvature singularities are a creation of general relativity and hence, in the absence of a quantum gravity, models of nonsingular black holes have received significant attention. We study the shadow (apparent shape), an optical appearance because of its strong gravitational field, cast by a nonsingular black hole which is characterized by three parameters, i.e., mass ($M$), spin ($a$), and a deviation parameter ($k$). The nonsingular black hole under consideration, is a generalization of the Kerr black hole {that} can be recognized asymptotically ($r>>k, k>0$) explicitly as the Kerr-Newman black hole, and in the limit $k \rightarrow 0$ as the Kerr black hole. It turns out that the shadow of a nonsingular black hole is a dark zone covered by {a} deformed circle. Interestingly, it is seen that the shadow of a black hole is affected due to the parameter $k$. Indeed, for a given $a$, the size of a shadow reduces as the parameter $k$ increases and the shadow becomes more distorted as we increase the value of the parameter $k$ when compared with the analogous Kerr black hole shadow. We also investigate, in detail, how the ergoregion of a black hole is changed due to the deviation parameter $k$.