Observational and theoretical aspects of superspinars

Abstract

This article delves into the observational signatures and theoretical underpinnings of rotating astrophysical objects, with a particular focus on superspinars -exotic objects characterized by preventing the formation of event horizons due to their high angular momentum. While solutions within General Relativity (Kerr superspinars) predict such objects, their classical forms harbor naked singularities, violate causality, and exhibit problematic repulsive gravitational effects. These characteristics render classical superspinars theoretically objectionable, leading to the consideration of them as physically implausible. On the other hand, the incompatibility between General Relativity and Quantum Mechanics suggests the exploration of alternative models, particularly those in which Quantum Gravity dominates the core and prevents the formation of scalar curvature singularities. This work demonstrates that superspinars without scalar curvature singularities can avoid all the complications associated with Kerr superspinars. Moreover, from a phenomenological standpoint, it is shown that the silhouettes of these superspinars could be markedly distinct from those of black holes and classical Kerr superspinars. To substantiate these differences, we perform a comprehensive analysis of inner null geodesics and investigate the structure of the Planckian region within superspinars without scalar curvature singularities. Our study reveals that only these superspinars provide the potential for distant observers to directly observe the extremely high curvature regions within their interiors.