Experiment on the mass-stripping of an interstellar cloud in a high Mach number post-shock flow

The high Mach number flow that follows an astrophysical shock can strip mass from interstellar clouds located in the flow. Eventually, the mass-stripping may fully strip the cloud, dispersing the entire cloud mass into the flow, and incidentally ending the cloud’s star formation. Experiments have been carried out at the Omega laser [T. R. Boehly, D. L. Brown, R. S. Craxton et al., Opt. Commun. 133, 495 (1997)], attempting to simulate and quantify the mass-stripping as it occurs when a shock passes through interstellar clouds. Ten laser beams with 5kJ of energy drive a strong shock into a cylinder filled with low-density foam with an embedded 120μm 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≈5ns), undergoing a classical Kelvin-Helmholtz roll-up (12ns) followed by a Widnall instability (30ns), an inherently 3D effect that breaks the 2D symmetry of the experiment. Material is continuously being stripped from the cloud at a rate that is shown to be inconsistent with laminar models for mass-stripping (the cloud is fully stripped by 80−100ns, ten times faster than the laminar model). A new model for turbulent mass-stripping is presented that agrees with the observed rate. The model should scale to astrophysical conditions and may also be used as a benchmark for hydrodynamic computer codes.