Light Rings, Accretion Disks and Shadows of Hayward Boson Stars

TL;DR

This study constructs Hayward boson star solutions using Einstein-Hayward gravity coupled with a complex scalar field, analyzing their optical features and the impact of quasi-horizon and light rings on their shadows.

Contribution

It introduces a numerical construction of Hayward boson stars and explores their optical appearance, highlighting differences caused by quasi-horizon presence.

Findings

Quasi-horizon radius and light ring radii increase with magnetic monopole charge.

Non-frozen states lack quasi-horizon, showing multiple photon rings in shadows.

Frozen states with quasi-horizon resemble Schwarzschild black holes with no extra photon rings.

Abstract

In this paper, we investigate the Einstein-Hayward gravity coupled to a complex scalar field without self-interaction. Using numerical methods, we construct a class of Hayward boson star solutions and examine their fundamental properties as well as the optical appearance of the accretion disk. Our results show that in the frozen state, both the quasi-horizon radius and the light ring radii increase with the magnetic monopole charge. Furthermore, using ray-tracing method, we find that for non-frozen states, the absence of an quasi-horizon results in the appearance of multiple photon rings within the shadow region of the accretion disks. In contrast, for frozen states, the presence of a quasi-horizon causes their images to resemble those of Schwarzschild black holes, with no additional photon rings appearing.