# Observability of spherical photon orbits in near-extremal Kerr black holes

## TL;DR

This paper studies spherical photon orbits in near-extremal Kerr black holes, showing their convergence on the horizon and the potential observability of multiple images due to light orbiting near the horizon.

## Contribution

It reveals the behavior of photon orbits in near-extremal Kerr spacetimes and their implications for observable black hole images.

## Key findings

- Photon orbits with certain impact parameters converge on the horizon.
- Weyl curvature near the horizon does not induce shear in these light rays.
- Multiple images from light orbiting near the horizon can be observable.

## Abstract

We investigate the spherical photon orbits in near-extremal Kerr spacetimes. We show that the spherical photon orbits with impact parameters in a finite range converge on the event horizon. Furthermore, we demonstrate that the Weyl curvature near the horizon does not generate the shear of a congruence of such light rays. Because of this property, a series of images produced by the light orbiting around a near-extremal Kerr black hole several times can be observable.