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Strong gravitational lensing by Kerr and Kerr-Newman black holes
Phys. Rev. D 103, 104063 – Published 28 May, 2021
DOI: https://doi.org/10.1103/PhysRevD.103.104063
Abstract
We study the strong gravitational lensing due to the Kerr black holes with angular momentum and the Kerr-Newman black holes with additional charge . We first derive the analytical expressions of the deflection angles of light rays that particularly diverge as they travel near the photon sphere. In this strong deflection limit, the light rays can circle around the black hole multiple times before reaching the observer, giving relativistic images. The obtained analytical expressions are then applied to compute the angular positions of relativistic images due to the supermassive galactic black holes. In this work, we focus on the outermost image with reference to the optical axis. We find that its angular separation from the one closest to the optical axis increases with the increase of angular momentum of the black holes for light rays in direct orbits. Additionally, the effects of the charge of black holes also increase the angular separation of the outermost image from the others for both direct and retrograde orbits. The potentially increasing observability of the relativistic images from the effects of angular momentum and charge of the black holes will be discussed.
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