Non-radial instability of stalled accretion shocks: advective-acoustic cycle

Abstract

The linear stability of stalled accretion shocks is investigated in the context of core collapse of type II supernovae. We focus on a particular instability mechanism based on the coupling of acoustic perturbations with advected ones (vorticity, entropy). This advective-acoustic cycle takes place between the shock and the nascent neutron star. Both adiabatic and non-adiabatic processes may contribute to this coupling, but only adiabatic ones are considered in this first approach. The growth time of the adiabatic instability scales like the advection time, and is dominated by low degree modes l=0,1,2. Non radial modes (l=1,2) found unstable by Blondin et al. (2003) can be related to this mechanism.