The interplay of reconnection and turbulence in relativistic plasmas: the case of black hole accretion flows and coronae

Massive black holes provide a unique environment for studying physical processes that cannot be investigated in the laboratory. A novel view of the black hole surroundings has recently been made available by the Event Horizon Telescope (EHT). EHT has provided images of the immediate vicinity of the supermassive black hole of the galaxy M87 and soon will deliver observations of Sagittarius A* at the center of our Milky Way galaxy. A large number of general relativistic magnetohydrodynamic (MHD) simulations have been performed to model the EHT data with different (but arbitrary) assumptions for the properties of the emitting electrons. Even though these models are very elaborate, they are unable to probe the physics of the emitting particles from the first principle. This is the realm of particle-in-cell (PIC) simulations. The planned research project will deploy PIC simulations and analytical tools to study the role of two fundamental plasma physical processes: (i) magnetic reconnection - the annihilation of oppositely directed magnetic fields, and (ii) turbulence which is responsible for powering the emission from the accretion flows feeding massive black holes. This research plan will tackle two aspects of the physics of plasmas near black holes: (i) determine the origin of the observed hard X-ray emission and test whether coronae are likely sources of Ultra High Energy Cosmic Rays (UHECRs), the most energetic particles in the Universe. This will be done by studying the self-consistent interplay of reconnection and radiation in the most magnetized regions ('coronae') around a luminous black hole; (2) study the development of turbulence and reconnection in low-luminosity accretion flows feeding a supermassive black hole. The project is expected to help better understand the properties of ions and electrons. Since electrons dominate the emission, this will be of paramount importance to produce more accurate models to compare with EHT observations.