High-Energy Plasma Phenomena in Astrophysics

19 - 30 July 2021

Elena Amato, Andrei Beloborodov, Frank Jenko, Anatoly Spitkovsky

The topic of this MIAPP program is dissipative processes in astrophysical plasmas that generate energetic particles and nonthermal emission. The most powerful sources of nonthermal emission are compact objects: neutron stars and black holes, which produce relativistic jets and energetic explosions. These objects involve physics at its extreme and continue to surprise us. Recent remarkable discoveries include observations of mergers of neutron stars, cosmological fast radio bursts (FRBs), and the first image of a supermassive black hole in nearby galaxy M87.

The ultimate energy source for compact objects is gravity. Typically, the released gravitational energy is first transformed into kinetic energy (a rotating accretion disk, a spinning neutron star, a relativistic jet) and also stored in a generated magnetic field. Then the energy is dissipated through processes that will be discussed at the program: shocks, electric discharge, magnetic reconnection, and turbulent cascades, energizing plasma particles. Dissipation of magnetic energy is particularly intriguing; it plays a key role in high-energy astrophysics and yet so far is poorly understood. The role of plasma instabilities is especially prominent in transient phenomena, and strong connections are emerging between plasma physics and time-domain astronomy, a quickly developing observational field. Plasma physics also plays an increasing role in multi-messenger astronomy where main targets are energetic compact objects capable of producing neutrinos, gravitational waves, and nonthermal radiation.

Current efforts to understand plasma behavior lay the foundations for the future of high-energy astrophysics, and the program will facilitate progress in this direction. The program will focus on numerical simulations and analytic models that shed light on plasma instabilities and dissipation mechanisms in high-energy phenomena, in particular in compact objects but also on large scales up to galaxy clusters. The program will bring together experts in different simulation methods and foster exchange of ideas. The methods include relativistic MHD simulations, kinetic plasma codes using particle-in-cell (PIC) or grid-based (Vlasov) techniques, and hybrid plasma simulations (fluid plasma + kinetic energetic particles). An important new direction is techniques to incorporate radiative processes and creation of electron-positron pairs in simulations of shocks and magnetic reconnection. This advance is essential for the studies of energy release around compact objects and high-power explosive phenomena, where radiative losses influence the plasma behavior.