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

A generalization of the Majumdar-Papapetrou multi-black-hole spacetime was recently constructed by Teo and Wan [Phys. Rev. D 109, 044054 (2024)], 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.