Surface temperature of an accretion disk around a wormhole Kerr-mimicker

Abstract

It has been suggested that spinning wormholes may mimic Kerr black holes in astronomical sources such as X-ray binaries and supermassive compact objects in centers of galaxies. With recent advances in instrumentation this could be tested if clear differences between wormhole and black hole accretion were identified. We aim to quantitatively determine the extent to which the orbital properties of test particles in the gravity of a spinning wormhole may differ from those of a Kerr black hole. We seek to find an observable related to disk accretion that would be clearly different for Kerr black holes and Kerr-like wormholes. We use the standard Lagrangian approach to derive the orbital properties of test particles from an effective potential. We use standard thin disk theory to infer the disk surface temperature. We find that at a given circumferential radius the physical quantities relating to circular orbits in the equatorial plane are exactly the same for the spinning wormhole and a black hole of the same mass and angular momentum, if only the two space-time metrics differ in the g_rr component alone. However, for a wormhole there are no orbits of radius less than that of its throat. Non-circular orbits, bound or unbound, are affected by the radial distance function; in particular, the angle of apsidal precession in Kerr-like wormholes will differ from that in Kerr black holes. A Kerr-like wormhole is a perfect black hole mimicker in relation to the orbital properties in the equatorial plane. The angular velocity, specific energy, specific angular momentum, and Lense-Thirring precession rate are the same for a Kerr black hole and a Kerr-like wormhole in circular orbits of the same circumference. We find that the area of the (geometrically thin) accretion disk is different, and this yields a visibly suppressed disk temperature for traversable wormholes with a sufficiently wide throat.