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

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. *

Imaging a boson star at the Galactic center

“…We plan to develop similar simulations as presented in this paper for self-interacting boson stars that would allow modeling supermassive compact objects with a much higher boson mass. We also note that Horvat et al (2013) studied boson stars non-minimally coupled to gravity. This is another direction of generalization for the present work.…”

Spinning boson stars and hairy black holes with nonminimal coupling

“…The transformation given by eqs. (34,35) therefore maps a solution of the field equations (2), (3) to a solution that extremizes (36). The transformation is independent of any assumption of symmetry and, in this sense, it is covariant; one can easily infer that the transformation is one-to-one in general.…”

“…We start by supposing the existence of a static BH solution in the original Jordan frame. Since the transformation (34,35) preserves symmetries and the structure of the light cone, this results in a BH solution in the Einstein frame. However, this contradicts a well known no-hair theorem, 49 that applies for a scalar field minimally coupled with gravity.…”

“…The spherically symmetric asymptotically flat BHs with generic ξ cannot support nonminimally coupled spatially regular neutral scalar fields. [21][22][23][24] investigated, 30,33,34 in which case only solitonic solutions are possible. In this paper we report spinning BHs and BH solutions with synchronised hair of the Einstein-(complex, massive) Klein-Gordon equations with a nonminimal coupling ξΨ * ΨR, extending previous results 12,35 to this case.…”

Retrolensing by a charged black hole

“…Since Darwin pointed out that faint images near the circular orbit of a light ray called light sphere or photon sphere [7,8] appear in the Schwarzschild spacetime in 1959 [9], the study of the gravitational lensing phenomena was revived several times [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24]. The gravitational lensing by the light sphere in various black hole spacetimes [17,, naked singularity spacetimes [17,[54][55][56], boson star spacetimes [57][58][59], and wormhole spacetimes [18,56,[60][61][62][63][64], was also investigated.Recently, LIGO reported a gravitational-wave event GW150914 [65] and showed the existence of heavy stellar-mass black holes with the mass M ≥ 25M ⊙ in nature [66]. Black holes become an important subject in astronomy and astrophysics, and gravitational lensing by black holes will be an important tool to study dim and isolated black holes.Holz and Wheeler [67] proposed to survey retrolensing caused by sun lights which were reflected by the light sphere of stellar-mass black holes near the solar system in 2002.…”