Circular Orbits Structure and Thin Accretion Disks around Kerr Black Holes with Scalar Hair

TL;DR

This study explores the structure of equatorial circular orbits and thin accretion disks around Kerr black holes with scalar hair, revealing unique features and potential observational signatures that distinguish them from standard Kerr black holes.

Contribution

It provides a detailed analysis of orbit structures and accretion disk properties around Kerr black holes with scalar hair, highlighting features that could help identify such objects observationally.

Findings

Distinct orbit structures compared to bald Kerr black holes

Diverse luminosity profiles depending on scalar charge and spin

Potential to constrain scalar charge through observational data

Abstract

In this paper we first investigate the equatorial circular orbit structure of Kerr black holes with scalar hair (KBHsSH) and highlight their most prominent features which are quite distinct from the exterior region of ordinary bald Kerr black holes, i.e. peculiarities that arise from the combined bound system of a hole with an off-center, self-gravitating distribution of scalar matter. Some of these traits are incompatible with the thin disk approach, thus we identify and map out various regions in the parameter space respectively. All the solutions for which the stable circular orbital velocity (and angular momentum) curve is continuous are used for building thin and optically thick disks around them, from which we extract the radiant energy fluxes, luminosities and efficiencies. We compare the results in batches with the same spin parameter $j$ but different normalized charges, and the profiles are richly diverse. Because of the existence of a conserved scalar charge, $Q$, these solutions are non-unique in the $(M, J)$ parameter space. Furthermore, $Q$ cannot be extracted asymptotically from the metric functions. Nevertheless, by constraining the parameters through different observations, the luminosity profile could in turn be used to constrain the Noether charge and characterize the spacetime, should KBHsSH exist.