Stability of planar accretion shock fronts*

Accretion shocks accompany stagnation, propagating into a fluid incident at an obstacle at supersonic velocity. Examples are the impacts of laser-driven foils (M. Karasik et al., Phys. Plasmas 17, 056317, 2010) or inverse z-pinch plasma flows (S. Merlini et al., arXiv:2306.01847v1) on stationary obstacles. Accretion shocks are not isolated, maintaining a causal contact between the obstacle and the shock front. Hence, the results of the planar shock-front linear stability analysis pioneered in the 1950s by D’yakov and Kontorovich (DK) for isolated shock waves are not directly applicable to the accretion shocks. We report theoretical and numerical analysis of the planar accretion shock front stability problem that puts to rest some long-standing controversies. We have found new eigenmodes of the spontaneous acoustic emission accompanying the DK instability and calculated the growth rate of 1D instability associated with normally incident sound-wave amplification at the shock front.