Light rings and light points of boson stars

TL;DR

This paper investigates photon trajectories around rotating boson stars, revealing unique light rings and points, and explores their relation to the stars' high compactness and ergoregions.

Contribution

It introduces the concept of light points—stable photon orbits at rest—specific to boson stars and analyzes their connection to ergoregions.

Findings

Identification of stable light rings and light points around boson stars

Link between light points and the presence of ergoregions

High compactness of boson stars allows for relativistic photon orbits

Abstract

This work is devoted to the study of photon trajectories around rotating boson stars. The basic properties of boson star models are given with a particular emphasis on the high compactness those objects can have. Using an effective potential method, circular orbits of photons around rotating boson stars are then obtained, at least for relativistic enough configurations. A particular class of light rings, in which the photons are at rest on a stable orbit, is exhibited. By this one means that the associated worldline is collinear to the Killing vector corresponding to the asymptotic time translation symmetry. It is proposed to call those orbits light points. Their existence is very specific to boson stars and the link between light points and ergoregions is investigated.