Shadow of Rotating Black Hole Immersed in Dark Matter Halo

Abstract

The recent black hole shadow observations by the Event Horizon Telescope provide a unique opportunity to probe both the strong gravity regime and the environment surrounding supermassive black holes. Since dark matter halos are expected to exist around galactic-center black holes, they may leave observable signatures on black hole shadows. In this work, we investigate the spacetime structure, photon dynamics, and shadow properties of a rotating black hole immersed in a generalized double power law dark matter halo. Starting from a static dark matter black hole solution, we employ the Newman--Janis algorithm to construct its rotating counterpart and obtain a Kerr-like metric with a dark matter-modified mass function. We analyze the horizon structure, ergosphere, and unstable spherical photon orbits, and find that the dark matter halo generally enlarges the horizon, shifts the photon shell outward, and modifies the black hole shadow. The effects become more pronounced for rapidly rotating black holes. Using the shadow observation of Sgr A*, we further constrain the dark matter halo parameter space and identify correlations among the halo parameters, black hole spin, and observer inclination angle. Our results suggest that black hole shadow observations provide a promising probe of dark matter distributions near supermassive black holes.