Multiscale Phenomena in Plasma Astrophysics

Coordinators: Eliot Quataert, Christopher Reynolds, Anatoly Spitkovsky, and Ellen Zweibel

Scientific Advisors: James Drake and Alexander Schekochihin

Most of the observable matter in the Universe is in the form of plasma, or tenuous ionized gas, and the complicated behaviors of plasmas underlie many astrophysical processes. Kinetic instabilities and collective effects in plasmas are responsible for particle acceleration, heating, and dissipation of free energy. These intrinsically microscopic processes affect the appearance of macroscopic astrophysical systems such as supernova remnants or accretion disk coronae, and must be included in large-scale models. The macroscopic evolution can also affect the small-scale physics, necessitating the solution of coupled multiscale problems that go beyond the simple parameterization of microphysics.

This program will facilitate progress on astrophysical problems that involve the coupling between microscopic plasma scales and macroscopic observables. We will focus on three areas where recent progress in the understanding of microphysics allows the study of new macroscale astrophysical connections: 1) acceleration and dynamics of galactic cosmic rays and their role in cosmic ray-driven galactic winds; 2) collisionless accretion flows around black holes and the emission signatures of disks, jets and coronae; and 3) the transport properties of magnetized turbulent plasmas and their effect on the structure of intracluster medium in galaxy clusters. Despite large differences in astrophysical context, these areas are surprisingly similar in the plasma processes involved, and researchers working in these subfields will strongly benefit from extended dialog. Computational tools that have been developed to study microphysical plasma processes are also broadly similar across these subfields. The program will devote special attention to developing and comparing new numerical techniques for bridging the multiscale divide between the kinetic plasma models and global simulations of astrophysical systems.