We present two-dimensional numerical simulations of an isothermal turbulent gas undergoing gravitational collapse, aimed at testing for the presence of ``logatropic'' behavior, as indicated by the evolution of the turbulent velocity dispersion as the density increases during the collapse. A logatropic behavior would require that Delta v ~ rho (-1/2) , which, however, is not verified in the simulations. Instead, the velocity dispersion increases with the density, in a process reminiscent of the temperature increase upon compression of an ideal gas, although in the present case the change in the ``internal energy'' of the turbulent gas is due to an increase of both the density and the speed of the fluid parcels. We thus suggest that the logatropic ``equation of state'' represents only the statistically most probable state of an ensemble of virialized clouds, but does not adequately represent the behavior of the ``turbulent pressure'' within a single cloud undergoing a thermodynamic process.
American Astronomical Society Meeting Abstracts
- Pub Date:
- December 1996