Princeton University 2020 Summer Colloquium Series

Recent radio observations of emission from infalling and outflowing plasma in the vicinity of supermassive black holes is linked to simple phenomenological models via general relativistic magnetohydrodynamic simulations and related analytic models. For Sagittarius A* in our Galactic Center, movies simulating hourly timescales show that these models aggregate into at least four morphological types: 1.) thin, asymmetric photon ring; 2.) coronal boundary layer with thin photon ring; 3.) thick photon ring; and 4.) extended outflow. For M87, further models are input into a jet simulation and compared with Very Long Baseline Array (43 GHz) observations. A self-similar, stationary, axisymmetric model based on a force-free flow in the jet simulation is then used to generate Stokes maps at Global mm-VLBI Array (86 GHz) and Event Horizon Telescope (230 GHz) scales. This model varies plasma content from ionic (e-p) to pair (e-e+). Emission at the observed frequency is assumed to be synchrotron radiation from electrons and positrons, whose pressure is set to be constant fractions of the local magnetic pressure. The cleanest observational signature in the Stokes maps is the vanishing of circular polarization for increasing positron content.