Thierry Foglizzo (Laboratoire de Modélisation des Plasmas Astrophysiques, CEA-Saclay). From the dynamics of a hydraulic jump to the supernova explosion of massive stars.

The explosion mechanism of massive stars is a challenging problem where multidimensional instabilities seem to play a central role. Non axisymmetric instabilities such as the Standing Accretion Shock Instability and neutrino-driven convection are able to break the spherical symmetry and impact the birth condition of pulsars. Surprisingly, the SASI instability can be illustrated with a simple experiment based on a shallow water analogy. The SWASI fountain involves a circular hydraulic jump in a radial converging flow, which becomes oscillatory and turns into a self sustained rotating pattern. Numerical simulations and a perturbative analysis suggest that this unstable dynamics is due to the interaction of vorticity and surface gravity waves. Our experimental setup uses the global rotation of the fountain to study the redistribution of angular momentum in the collapsing stellar core. Differential rotation feeds a m=1 spiral wave reminiscent of the corotation instability. A new experiment 6 times larger challenges our theoretical understanding of this system.