Imprints of dark matter on black hole shadows using spherical accretions

Abstract

We study the possibility of identifying dark matter in the galactic center from the physical properties of the electromagnetic radiation emitted from an optically-thin disk region around a static and spherically symmetric black hole. In particular, we consider two specific models for the optical-thin disk region: a gas at rest and a gas in a radial free fall. Due to the effect of dark matter on the spacetime geometry, we find that the dark matter can increase or decrease the intensity of the electromagnetic flux radiation depending on the dark matter model. To this end, we analyze two simple dark matter models having different mass functions {mathcal {M}}(r), with a matter mass M, thickness Delta r_s along with a dark matter core radius surrounding the black hole. In addition to that, we explore the scenario of a perfect fluid dark matter surrounding the black hole. We show that in order to have significant effect of dark matter on the intensity of the electromagnetic flux radiation, a high energy density of dark matter near the black hole is needed. We also find that the surrounding dark matter distribution plays a key role on the shadow radius and the intensity of the electromagnetic flux radiation, respectively. Finally we have used the relation between the shadow radius and the quasinormal modes (QNMs) to compute the real part of QNM frequencies.