Ultra-high-resolution imaging breakthroughs are revolutionizing our understanding of how black holes interact with their environments. The iconic image by the Event Horizon Telescope shows the “shadow” of the M87 black hole, silhouetted against the glowing plasma swirling around it. The basic dynamics of these accretion flows has been studied in general-relativistic magnetohydrodynamic (GRMHD) simulations that show the development of turbulence driven by the magnetorotational instability (MRI) and intermittent large magnetic structures.

However, in isolation such studies are inadequate because radiation is emitted by the electrons alone and we do not understand the electron kinetics. The only way to connect observations of accreting black holes to the physical nature of accretion flows, as revealed by the GRMHD simulations, is with detailed study of electron (and ion) kinetics. Using petascale 3D particle-in-cell simulations, this project investigates electron versus ion energization; nonthermal particle acceleration; and self-consistent synchrotron radiation, for three processes characteristic of black-hole accretion: MRI-driven turbulence, externally driven turbulence, and collisionless magnetic reconnection. These studies will be done in the relativistic or “semi-relativistic” (relativistic electrons but non-relativistic ions) regimes relevant to black-hole accretion flows.

This work takes a critical step toward understanding the behavior of black holes in the universe. Moreover, these simulations of 3D electron-ion MRI turbulence and reconnection have the potential to significantly advance computational plasma physics.