Dark matter effect on the weak deflection angle by black holes at the center of Milky Way and M87 galaxies

Abstract

In this paper, we investigated the effect of dark matter on the weak deflection angle by black holes at the galactic center. We consider three known dark matter density profiles such as the Cold Dark Matter, Scalar Field Dark Matter, and the Universal Rotation Curve from the Burkert profile. To achieve this goal, we used how the positional angles are measured by the Ishihara et al. method based on the Gauss–Bonnet theorem on the optical metric. With the help of the non-asymptotic form of the Gauss-Bonnet theorem, the longitudinal angle difference is also calculated. First, we find the emergence of apparent divergent terms on the said profiles, which indicates that the spacetime describing the black hole-dark matter combination is non-asymptotic. We showed that these apparent divergent terms vanish when the distance of the source and receiver are astronomically distant from the black hole. Using the current observational data in the Milky Way and M87 galaxies, we find interesting behaviors of how the weak deflection angle varies with the impact parameter, which gives us some hint on how dark matter interacts with the null particles for each dark matter density profile. We conclude that since these deviations are evident near the dark matter core radius, the weak deflection angle offers a better alternative for dark matter detection than using the deviation from the black hole shadow. With the dark matter profiles explored in this study, we find that the variation of the values for weak deflection angle strongly depends on the dark matter mass on a particular profile.

Testing Symmergent gravity through the shadow image and weak field photon deflection by a rotating black hole using the M87$^*$ and Sgr. A$^*$ results

“…In 2008, Gibbons and Werner used the Gauss-Bonnet theorem (GBT) on the optical geometries in asymptotically flat spacetimes and calculated the weak deflection angle first time in literature [26]. Afterwards, this method has been applied to various related phenomena [27][28][29][30][31][32][33][34][35][36][37][38][39][40][41]. One of the aims of this paper is to probe Symmergent gravity through the black hole's weak deflection angle using GBT and also shadow silhouette as perceived by a static remote observer.…”

Testing dynamical torsion effects on the charged black hole's shadow, deflection angle and greybody with M87* and Sgr A* from EHT

“…Since then, the formalism was applied to a number of static and spherically symmetric black hole spacetime models to explore how certain parameters induce deviations from the known black hole shadow size . Pantig et al [72,73] have studied the possible effects of dark matter on a Schwarzschild black hole with the correction of extended uncertainty principle on black hole shadow and also effect of dark matter on the weak deflection angle by black holes at the galactic center. Övgün has showed [74] that a confining charge gives a significant contribution to the shadow of the black hole with confining electric potential in scalar-tensor description of regularized 4dimensional Einstein-Gauss-Bonnet gravity.…”

Quasinormal modes of Kerr-like black bounce spacetime

“…Alternative theories of gravity are extension of the form of Einstein's GR through various methods, has output of different field equations, hence different black hole solutions and cosmological models. Nowadays, alternative theories of gravity and their applications are a playground of physicist, provide a basis for the now-known understanding of physical phenomena of the universe [26][27][28][29][30][31][32][33][34][35][36][37][38]. The spectrum of known stationary black hole solutions in modified gravity theories has dramatically in-creased, sometimes in unexpected ways.…”