Light rings and light points of boson stars

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.

Testing the nature of dark compact objects: a status report

“…5. Once spin [189] or nonlinear interactions [86,187,188] are added, boson star spacetimes can have light rings and ergoregions. The stressenergy tensor of a self-interacting bosonic field contains anisotropies, which in principle allow to evade naturally Buchdahl's theorem.…”

Shadows and strong gravitational lensing: a brief review

“…Any null vector tangent to a LR is spanned by a combination of ζ, ξ, and it thus geometrically anchored to these symmetries. As a curious particular case, static LRs are possible in some spacetimes; an example occurs at the onset of formation of an ergotorus [23]. For a static LR ζ alone is always tangent to the LR orbit.…”

“…For a continuous family of spacetimes with the Killing vectors ζ,ξ, such as e.g. Boson or Proca stars [34][35][36], the number of LRs is not a constant (see [23,24]). However there is still a LR related topological quantity that is preserved [17].…”

“…Several spacetimes in the literature also feature LRs of the second category (b), with Proca/Boson stars [23][24][25] or the Majumdar-Papapetrou di-hole system [33] as possible examples. As was previously discussed, these LRs are expected to operate as a radiation trap, leading to a pile up of energy and to an eventual backreaction on the spacetime, possibly triggering a non-linear instability [26].…”

Static Orbits in Rotating Spacetimes

“…Orbits in boson star spacetimes have been considered e.g. in [4][5][6][7][8][9].) For the particular example, we choose a boson star without self-interaction with a boson mass m b = √ 1.1, a boson frequency ω s = 0.84, and a rotational quantum number m = 1.…”