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Radiative shocks are relatively common in astrophysics, occuring in accretion flows, stellar winds, stellar jets, supernovae, star formation, and perhaps galaxy formation. In some cases the cooled gas downstream of the radiative shock forms an isolated slab of dense gas. If this slab is bounded on the other side by a radiative shock as well, it is susceptible to a nonlinear dynamic instability (Vishniac, ApJ 428, 186). We have studied such shock-bounded slabs using numerical hydrodynamics. Sinusoidal perturbations were added to planar slabs to determine the characteristics of the dynamical evolution as a function of the wavelength and amplitude of the perturbation relative to the width of the slab. We confirm Vishniac's claim that perturbations with amplitudes larger than the width of the slab are dynamically unstable: the so-called "Nonlinear Thin Shell Instability" (NTSI). Given a suitable initial perturbation and a sufficiently large Mach number, the perturbation will grow unbounded. However, in many cases our results show that the breathing mode of the perturbed slab can "outrun" the shredding motion of the NTSI, causing the perturbations to pinch off and form a relatively flat, albeit thick, slab that remains confined in space. We have also investigated perturbations due to dense clouds advected into an unperturbed planar slab. These perturbations often lead to the NTSI effects as well.
This research was supported by an AAS REU award to North Carolina State University.
