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GR: Fachverband Gravitation und Relativitätstheorie

GR 12: Relativistic Astrophysics and Scalar Fields

GR 12.4: Talk

Thursday, March 23, 2023, 15:00–15:20, ZEU/0260

Image of the thin accretion disk in gravity with a minimally coupled scalar field — •Galin Gyulchev — Faculty of Physics, Sofia University, James Bourchier Boulevard, Sofia 1164, Bulgaria

We study possible observable images of a black hole and naked singularity described by rotating geometry in Einstein gravity, minimally coupled to a scalar field. We consider a Kerr-like (KL) alternative to the rotating Fisher-Janis-Newman-Winicour solution. Our study includes analytical and numerical calculations of equatorial circular orbits, shadow images, and radiation from thin accretion disks for various values of the object's angular momentum and scalar charge. The KL solution cannot be ruled out by the observations for small values of the scalar charge either. As the scalar charge increases, the optical properties change dramatically. The photon region does not hide the singularity, so it should be classified as a strong singularity. The shadow of the compact object can become multiply connected and strongly oblate. This new qualitative feature can be used to distinguish observationally black holes from naked singularities via the contemporary Very Long Baseline Interferometry experiments at short wavelengths.