Simulations of high-Mach-number collisionless perpendicular shocks in astrophysical plasmas.

A problem of critical importance to space physics and astrophysics is the existence and properties of high--Mach-number shocks. In this Letter we present the preliminary results of a simulation of a perpendicular shock with Alfven Mach number 22. We show that for sufficiently small electron resistivity the dissipation for this shock is provided by a periodic, rather than time-stationary, reflection of ions. We discuss the problem of electron heating and the extension to higher Mach numbers.