Formation of photon spheres in boson stars with a nonminimally coupled field

TL;DR

This paper demonstrates that photon spheres can form in certain boson star configurations with a nonminimally coupled scalar field, impacting gravitational lensing and photon flux in the star's core.

Contribution

It reveals the conditions under which photon spheres form in boson stars with nonminimal coupling, linking these structures to observable lensing phenomena.

Findings

Photon spheres can exist in boson stars with nonminimal coupling.

Presence of photon spheres affects gravitational lensing and photon flux.

Photon flux in the star's center can be significantly increased.

Abstract

A static, spherically symmetric, asymptotically flat spacetime may allow for circular, closed null-geodesics which are said to belong to a photon sphere. In the context of gravitational lensing in the strong deflection regime, the presence of a photon sphere leads to an unbounded angle of deflection of light (multiple turns) and formation of relativistic images. In this paper, we show that photon spheres may form in some configurations of boson stars constructed with a free massive complex scalar field nonminimally coupled to gravity. Assuming that the boson star is transparent to light, photon spheres would give raise not only to phenomena in the realm of strong gravitational lensing, but also to considerably increased photon flux in the central region of the star, relative to the flux in its surroundings.