Trapped photon region in the phase space of sub-extremal Kerr-Newman and Kerr-Sen spacetimes

TL;DR

This paper investigates the geometric structure of trapped photon regions in sub-extremal Kerr-Newman and Kerr-Sen spacetimes, revealing their topology and adapting existing methods to these specific black hole models.

Contribution

It extends the understanding of photon trapping regions by analyzing their topology in Kerr-Newman and Kerr-Sen spacetimes, adapting methods from Kerr spacetime analysis.

Findings

The trapped photon region projects to a 5D submanifold with topology SO(3)×R^2.

The analysis applies to sub-extremal Kerr-Newman and Kerr-Sen black holes.

The method adapts the approach used for Kerr spacetime to these more general cases.

Abstract

We analyse the geometry and topology of the trapped photon region in the domain of outer communication of sub-extremal Kerr-Newman and Kerr-Sen spacetimes. Specifically, we show that its projection to the (co-)tangent bundle forms a five-dimensional submanifold with topology $SO(3)\times \mathbb{R}^2$ in each setup. The proof adapts the method of Cederbaum and Jahns for sub-extremal Kerr spacetime.