PIC simulations of the magnetorotational instability (MRI) in stratified, collisionless accretion disks

The magnetorotational instability (MRI) is an MHD instability essential for outward transport of angular momentum in various astrophysical accretion disks. In very low-luminosity disks around black holes, such as in Sagittarius A* and M87, particle-particle Coulomb collisions occur very infrequently, which makes these accreting systems effectively "collisionless''. This characteristic gives rise to several kinetic plasma effects that could modify the MRI evolution and generate particle acceleration. We present results of 2D and 3D fully kinetic, particle-in-cell (PIC) plasma simulations of the collisionless MRI. Our simulations are local and stratified, which means that we use the local, shearing box approximation and self-consistently include the vertical structure of the disk. We concentrate on the sub-relativistic plasma regime, relevant at tens of gravitational radii from the central black hole, and quantify the ability of the MRI turbulence to transport angular momentum and to accelerate particles. We find that both angular momentum transport as well as particle acceleration in our stratified simulations are, on average, significantly more efficient than in the case where disk stratification is not included.