Observational signatures of thin accretion disks around rotating black holes embedded in dark matter halos

Abstract Black holes embedded in a dark matter background represent an important candidate model that extends the standard vacuum case, characterizing the strong gravitational environments at galactic centers and the gravitational influence of dark matter. This study focuses on dark matter halo-modified Kerr black holes and systematically investigates the observational characteristics of their surrounding thin accretion disks. Starting from static black hole solutions with dark matter halos, we employ the Newman–Janis algorithm to construct its rotating counterpart. The dark matter halo is modeled by a general double power-law density profile, whose integrated mass $$M_D(r)$$ M D ( r ) modifies the radial mass function of Kerr metric to $$m(r) = M + M_D(r)$$ m ( r ) = M + M D ( r ) . Based on this spacetime, we analyze the observational properties of their thin accretion disk, including the radiative flux, temperature, differential luminosity, and spectral luminosity as a function of radius, with respect to the black hole spin and dark matter halo parameters. Furthermore, by combining ray-tracing methods, we simulate the bolometric image of the thin accretion disk under different black hole spins, dark matter halo parameters, and viewing inclinations. The dark matter halo enhances the gravitational potential, shifting the event horizon, innermost stable circular orbit, and photon shell outward, suppressing the peak radiative flux, and producing a fainter image, thereby generating signatures that are possibly observational distinguishable from standard vacuum Kerr black holes.