Testing regularity of black holes with X-rays and Gravitational Waves

Physically relevant solutions in general relativity often contain spacetime singularities, which are typically interpreted as a sign of breakdown of the theory at high densities/curvatures. Hence, there has been a growing interest in exploring phenomenological scenarios that describe singularity-free black holes, gravitational collapses, and cosmological models. We examine the metric put forth by Mazza, Franzin & Liberati for a rotating regular black hole and estimate the regularization parameter $l$ based on existing X-ray and gravitational wave data for black holes. When $l=0$, the solution corresponds to the singular Kerr solution of general relativity, while a non-zero value of $l$ yields a regular black hole or a regular wormhole. The analysis reveals that the available data support a value of $l$ that is close to zero.