Collisionless accretion disks: a particle-in-cell simulation study of the magnetorotational instability (Mario Riquelme, University of California, Berkeley)

The accretion of gas in astrophysical disks requires outward transport of angular momentum, understood to be provided by the magnetorotational instability (MRI), as suggested by a number of numerical MHD studies. However, when the time scale for Coulomb collisions of the particles is longer than the inflow time of the gas, ions and electrons become thermally decoupled and the standard MHD approach is not directly applicable. These 'collisionless' disks are ubiquitous, occurring, for example, in low-hard state of X-ray binaries, and around supermassive black holes in the center of nearby galaxies and the Milky Way (Sgr A*). I will present my study of the MRI in collisionless accretion disks, using first-principles particle-in-cell (PIC) simulations. I will compare my results with the standard fluid approach, and will explain its consequences for the MRI dynamics and for the physics of particle heating and acceleration in collisionless disks.