Collisionless ion-electron energy exchange in magnetized astrophysical shocks

Magnetized collisionless shocks are ubiquitous in the universe, and energy partition in these shocks has long been an open question. Independent thermalization would predict a largely uneven energy partition because of the large ion-electron mass ratio, contradicting astronomical observations. Our kinetic simulations of low Mach number magnetized collisionless shocks show a significant energy exchange between ions and electrons in the downstream of the shocks, which implies a collisionless electron heating mechanism. A multi-fluid model indicates a resonance between electron whistler and ion magnetohydrodynamic waves may provide new mechanisms that account for the energy transfer from ions to electrons.