Optical characteristics of the Kerr–Bertotti–Robinson black hole

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 black hole shadow and 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 influence of the rotation parameter on the optical image of the Kerr–BR black hole is significant 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 BR-like magnetic fields surrounding them. 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 the black hole image, it is possible to detect the BR-like magnetic fields surrounding black holes.