Black holes are among the most remarkable predictions of Einstein's theory of gravity. Radio observations by the Event Horizon Telescope now resolve the gas flowing nearby the event horizon of the supermassive black hole at the center of our galaxy, SgrA*, and the black hole in the M87 galaxy. These spectacular observations revolutionize our understanding of the nature of extreme gravity, and the physics of supermassive black holes in the centers of galaxies. The difficulty in understanding the observed emission, however, lies not in the understanding black holes themselves, but rather the physics of plasmas that produce the radiation we observe. Progress in understanding plasma behavior is essential not only for interpreting observations, but also to test Einstein's theory of gravity in the extreme regime. The latter tests can only be carried out if uncertainties in understanding the nonlinear behavior of collisionless plasma are illuminated.

Our research uses accurate numerical models to explore plasma dynamics in the vicinity of a black hole and the radiation produced by energetic charged particles. Recent work includes first-principles models of reconnection-powered flares produced by accretion flows around SgrA* and M87* (paper 1, paper 2), pair-production discharges near the event horizon (paper 3), black hole magnetic ``balding’’ (paper 4) and first kinetic model of the black hole accretion (paper 5). Some of these investigations became possible with the first General-Relativistic Particle-in-cell code Sasha Philippov co-developed with Kyle Parfrey (PPPL) and Benoit Cerutti (Grenoble).