Spinning generalizations of Majumdar-Papapetrou multi-black hole spacetimes: light rings, lensing and shadows

TL;DR

This paper investigates the null geodesic dynamics, light rings, and gravitational lensing of a generalized multi-black hole spacetime with spinning, charged extremal black holes, revealing complex light ring configurations and shadow features.

Contribution

It extends the Majumdar-Papapetrou solution to include spinning black holes and analyzes their light rings and lensing effects using topological charge formalism and ray-tracing.

Findings

Multiple light ring configurations depending on angular momenta

Light rings with opposite topological charges can merge and annihilate

Shadow and lensing patterns resemble those of the double-Kerr spacetime

Abstract

A generalization of the Majumdar-Papapetrou multi-black hole spacetime was recently constructed by Teo and Wan [1], describing charged and spinning (extremal) balanced black holes in asymptotically flat spacetime. We explore the dynamics of null geodesics on this geometry, focusing on the two-center solution. Using the topological charge formalism, we show that various light ring arrangements arise from different choices of individual angular momenta: light rings with opposite topological charges can merge and annihilate each other, resulting in configurations with a total of 4, 6, or 8 light rings. Using backward ray-tracing, we obtained the shadow and lensing of these spacetimes. The former, in particular, closely resembles those for the double-Kerr metric.