Optical Appearance of Kerr Black Hole Surrounded by Cold Dark Matter

Abstract

In this work, we provide graphical representation of shadow images of Kerr-like black hole (BH) in the presence of cold dark matter (CDM) halo illuminated with two different accre- tion flow models. The impact of spin parameter a, critical density ρc and the scale radius Rs on the observed images of BHs is carefully addressed. The results indicate that as a in- creases, the circular orbits shifted towards the right, while the larger values of both ρc and Rs caused to enhance the radius of circular orbits of BH shadow. In the case of background light source, the impact of parameter ρc on shadow distortion is extremely negligible, but this influence is relatively small and becomes appreciable when the parameter Rs has larger values. Next, we expand the interior region of accretion disk to the BH event horizon, and consider the motion of particles inside and outside the regions of inner stable circular or- bit (ISCO). The results exhibit that the intensity as well as the radius of BH shadow are gradually increasing with the increase of both ρc and Rs. On the other hand, in the case of retrograde flow, the intensity of the shadow images significantly decreases and a crescent moon emerges in the top of the observer’s frame. Subsequently, we discuss the distinctive features of red-shift configurations for both prograde and retrograde flows. The obtained results interpret that the configuration of red-shifts and the visual signatures is associated to the behaviour of accreting flow as well as with relevant parameters. Finally, using the recent observational data of EHT results, we found the shadow radius of Sgr A∗ provides the best-fit parameter constraints as compared to M87∗.