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[42.15] Interfacial Instabilities Driven by Self-Gravity in the ISM: Onset and Evolution

R.M. Hueckstaedt, J.H. Hunter, Jr. (University of Florida)

As the sites of all present day star formation within the Milky Way, cold molecular clouds are a vital link in the evolution of tenuous interstellar gas into stars. Any comprehensive theory of star formation must include a study of the hydrodynamic processes that effect molecular cloud morphology. In the ISM, hydrodynamic instabilities and turbulence play large roles in shaping clouds and creating regions capable of gravitational collapse. One of the key forces in the interstellar environment is self-gravity. Regardless of the mechanism initially responsible for creating density enhancements, self-gravity must ultimately drive the final collapse. A recent study has shown that self-gravity also gives rise to an interfacial instability that persists in the static limit when a density discontinuity exists (Hunter, Whitaker & Lovelace 1997). This instability also persists in the absence of a constant gravitational acceleration, unlike the familiar Rayleigh-Taylor instability. Analytic studies in Cartesian geometry predict that for perturbations proportional to exp(-i{\omega}t), the instability has an incompressible growth rate {\omega}²=-2{\pi}G(\rho₁-\rho₂)²/(\rho₁+\rho₂). The growth rate is independent of the perturbation wavelength. Studies have also included cases in cylindrical geometry in which a static density interface has proven stable to kink modes but unstable to sausage modes. In the case of sausage modes, (perturbations in the radial direction), there exists a critical wavelength below which the instability does not appear. In this paper, we present two-dimensional numerical models designed to examine this self-gravity driven instability. A hydrodynamic code with self-gravity is used to test the analytic predictions in Cartesian and cylindrical geometries and to follow the instability into the nonlinear regime. We consider how the growth of hydrodynamic instabilities, including self-gravity driven instabilities, can have a role in shaping the ISM. We discuss implications for molecular cloud structure and core collapse.

The author(s) of this abstract have provided an email address for comments about the abstract: hueckst@astro.ufl.edu

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