Smoothness of the future and past trapped sets in Kerr-Newman-Taub-NUT spacetimes

TL;DR

This paper analyzes the structure of trapped null geodesics in Kerr-Newman-Taub-NUT spacetimes, revealing that from an observer's perspective, trapping corresponds to two smooth sets of spacelike directions on their celestial sphere.

Contribution

It demonstrates that the future and past trapped null geodesics form two smooth sets of directions on the celestial sphere for observers outside the black hole.

Findings

Trapped null geodesics form smooth sets of directions.

Trapping can be characterized geometrically on the celestial sphere.

The analysis applies to sub-extremal Kerr-Newman-Taub-NUT spacetimes.

Abstract

We consider the sets of future/past trapped null geodesics in the exterior region of a sub-extremal Kerr-Newman-Taub-NUT spacetime. We show that, from the point of view of any timelike observer outside of such a black hole, trapping can be understood as two smooth sets of spacelike directions on the celestial sphere of the observer.