How do black holes shine: Multiwavelength emission in the high-energy Universe

Astrophysical black holes are surrounded by accretion disks, jets, and coronae consisting of magnetized, (near)-collisionless relativistic plasma. They produce observable high-energy radiation in the form of flares and it is currently unclear where and how this emission is exactly produced. The radiation typically has a non-thermal component, implying a power-law distribution of emitting relativistic electrons. Magnetic reconnection is a viable mechanism to tap the large reservoir of magnetic energy in these systems and accelerate electrons to extreme energies. The accelerated electrons can then emit high-energy photons that themselves may strongly interact with the plasma, rendering a highly nonlinear system. Modeling these systems necessitates a combination of magnetohydrodynamic models to capture the global dynamics of the formation of dissipation regions, and a kinetic treatment of plasma processes that are responsible for particle acceleration, pair creation and annihilation, and radiation. I will present novel studies of accreting black holes and how they radiate in regions close to black hole event horizon, using both first-principles general relativistic kinetic particle-in-cell simulations and global large-scale three-dimensional magnetohydrodynamics models. I will answer the question of how well fluid-type models like magnetohydrodynamics can capture magnetic reconnection in collisionless plasmas around black holes. With a combination of models, I determine where and how dissipation of magnetic energy occurs, and what kind of emission signatures are typically produced.