Simulations of images of accretion discs around Kerr black holes relevant to M87*

ABSTRACT Supermassive black holes (SMBHs) like M87* and Sgr A* have been observed with the Event Horizon Telescope (EHT), facilitating the investigation of null geodesics near a black hole. The null geodesic around black holes and relevant features such as photon ring, lensing ring and black hole shadow, have been modelled analytically. The emission and absorption of plasmas surrounding a black hole is highly related to the physical quantities such as mass density, momentum, internal energy, magnetic field, black hole spin, and angular momentum. The images of accretion discs around black holes are affected by Doppler shift, gravitational redshift, and frequency-dependent emissivity and absorption coefficient, which can be assessed by numerical simulations. In this work, a numerical ray-tracing scheme and a covariant radiative transfer scheme are proposed to simulate the photon trajectories emitting from the accretion discs around Kerr black holes, hence to reconstruct their images. A set of magnetized, geometrically thick accretion discs are adopted to compute the emissivity and absorption coefficient, which are then used to reconstruct the images of the subject accretion discs. The effects of magnetization, black hole spin, angular momentum and geometry of the discs are studied. The effects of Doppler shift, gravitational lensing, and frequency-dependent emissivity and absorption coefficient are investigated by simulations.