Accretion disk luminosity around rotating naked singularities

Abstract

We explore circular geodesics of neutral test particles in the gravitational field of a rotating deformed mass. The geometry around this source is described by the Quevedo–Mashhoon solution, which corresponds to a naked singularity. To this end, we compute the orbital parameters of test particles in the equatorial plane, such as the angular velocity $\Omega$, energy $E$ and angular momentum $L$, per unit mass. We also numerically estimate the radius of the innermost stable circular orbit $r_{ISCO}$. In addition, we consider a simple model for the disk’s radiative flux, differential luminosity, and spectral luminosity, employing the well-known Novikov–Page–Thorne model. We mainly focus on the flux of the accretion disk around several rotating naked singularities possessing the same mass and quadrupole moment but different rotation and deformation parameters. We analyze the possibility of distinguishing Kerr black holes from rotating naked singularities. The astrophysical implications of the results obtained are discussed.