A variety of astrophysical phenomena can only be explained as being powered by black holes. In particular, accreting supermassive black holes are responsible for launching relativistic plasma jets and for accelerating ultra energetic particles. The mechanism that channels energy from the black hole to the particles remains a mystery.
Observations have come to help lately. The Event Horizon Telescope collaboration has been able to image the shadow of the supermassive black hole M87*, suggesting that it might be spinning. The GRAVITY collaboration detected a hot spot in infrared orbiting Sgr A*, indicating the presence of a large scale poloidal magnetic field. These observations give new clues to constrain theoretical models that are able to explain jets and particle acceleration.
This problem involves complex interactions between collisionless plasma dynamics in high gravitational field, and pair creation due to the interaction of energetic particles with surrounding photons from the accretion flow. Only kinetic simulations can capture all these effects.
In this talk, I will present General Relativistic Radiative Particle-in-Cell (GRRPIC) simulations of an axisymmetric black hole magnetosphere possessing a monopolar magnetic field, embedded in a soft background radiation field. These simulations use newly developed radiative transfer techniques. They show for the first time the development of a time-dependent electromagnetic cascade, which could explain the high variability of high-energy emission from Sgr A* and M87*, and plasma loading at the base of relativistic jets.