Experiment on the Mass Stripping of an Interstellar Cloud Following Shock Passage

The interaction of supernova shocks and interstellar clouds is an important astrophysical phenomenon which can lead to mass stripping (transfer of material from cloud to surrounding flow, "mass loading" the flow) and possibly increase the compression in the cloud to high enough densities to trigger star formation. Our experiments attempt to simulate and quantify the mass stripping as it occurs when a shock passes through interstellar clouds. We drive a strong shock (and blast wave) using 5 kJ of the 30 kJ Omega laser into a cylinder filled with low-density foam with an embedded 120 μm Al sphere simulating an interstellar cloud. The density ratio between Al and foam is ~9. Time-resolved X-ray radiographs show the cloud getting compressed by the shock (t ≈ 5 ns), undergoing a classical Kelvin-Helmholtz roll-up (12 ns) followed by a Widnall instability (30 ns), an inherently three-dimensional effect that breaks the two-dimensional symmetry of the experiment. Material is continuously being stripped from the cloud at a rate which is shown to be considerably larger than what is predicted by laminar models for mass stripping; the cloud is fully stripped by 80-100 ns, 10 times faster than the laminar model. We present a new model for turbulent mass stripping that agrees with the observed rate and that should scale to astrophysical conditions, which occur at even higher Reynolds numbers than the current experiment.