Highly Compressible MHD Turbulence and Gravitational Collapse

Abstract

We investigate the properties of highly compressible turbulence and its ability to produce self-gravitating structures. The compressibility is parameterized by an effective polytropic exponent gama-eff. In the limit of small gama-eff, the density jump at shocks is shown to be of the order of e^{M^2}, and the production of vorticity by the nonlinear terms appears to be negligible. In the presence of self-gravity, we suggest that turbulence can produce bound structures for gama-eff < 2(1-1/n), where 'n' is the typical dimensionality of the turbulent compressions. We show, by means of numerical simulations, that, for sufficiently small gama-eff, small-scale turbulent density fluctuations eventually collapse even though the medium is globally stable. This result is preserved in the presence of a magnetic field for supercritical mass-to-flux ratios.