Multi-level images around Kerr-Newman black holes

TL;DR

This paper analyzes gravitational lensing and multi-level images around Kerr-Newman black holes, deriving analytic lens equations and exploring how black hole charge influences higher-order images.

Contribution

It provides new analytic forms of lens equations in Kerr-Newman spacetime and examines the impact of black hole charge on multiple image formations.

Findings

Charge significantly affects higher-order images.

Derived approximate forms of lens equations near photon orbits.

Analyzed images of spherical and disk-like luminous sources.

Abstract

We study the lensing effects of Kerr-Newman (KN) black holes and the multi-level images of luminous sources around the black holes. We obtain the analytic forms of the lens equations in KN spacetime and derive approximately their limiting forms for photon emissions near the bounded photon orbits. After deriving the expressions of three key parameters $\gamma$, $\delta$ and $\tau$, we investigate the primary, the secondary and the higher-order images of spherical sources and equatorial disk-like sources. In particular, we find that the charge of KN black hole has a significant effect on the higher-order images.