Optical Characteristics of the Kerr-Bertotti-Robinson Black Hole

TL;DR

This paper studies the optical images of Kerr-Bertotti-Robinson black holes, revealing how magnetic fields and rotation influence their shadows and rings, and discusses potential observational constraints using real black hole data.

Contribution

It provides the first detailed analysis of the optical characteristics of Kerr-BR black holes, highlighting the effects of magnetic fields and rotation on observable features.

Findings

Magnetic field increases the size of the black hole shadow and Einstein ring.

Rotation parameter affects the optical image differently than magnetic field.

Data from M87* and Sgr A* can constrain the magnetic field around black holes.

Abstract

The Kerr-Bertotti-Robinson (Kerr-BR) black hole, a theoretical model of a rotating black hole immersed in a uniform magnetic field, has been proposed recently by Podolsky and Ovcharenko. This study investigates the optical characteristics of the Kerr-BR black hole based on the exact solution. We analyze the optical image under two illumination models: a celestial light source and a geometrically thin accretion disk. We reveal distinct roles for the fundamental parameters in the model. Specifically, it is found that under both illumination models, the effect of the rotation parameter on the optical image of the Kerr-BR black hole is significantly different from that of the magnetic field. As the magnetic field increases, the radii of both the shadow and the Einstein ring enlarge. We also attempt to use the data from M87* and Sgr A* to constrain the magnetic field. These results enhance our understanding of the optical characteristics of the Kerr-BR black hole and establish a theoretical foundation for interpreting future observations on the optical image of the black hole immersed in a uniform magnetic field. Finally, we point out that with advances in the resolution of black hole images, it is possible to detect potential BR-like magnetic fields around black holes.