KELVIN-HELMHOLTZ AND THERMAL-DYNAMIC INSTABILITIES WITH SELF-GRAVITY - A NEW GRAVITATIONAL INTERFACE INSTABILITY

In the vortex sheet limit, we generalize our previous work on compress ible, anisentropic Kelvin-Helmholtz, and related instabilities by incl uding self-gravity in the calculations. In addition to significantly m odifying the Kelvin-Helmholtz modes, if the background media are of un equal density, self-gravity gives rise to a new instability that persi sts in the static limit. If the media have significant density contras t (rho(1)/rho(2)=1/2, say), the growth rate of this new gravitational interface instability is of the order of the free-fall time in the den ser medium, and, unlike a Jeans instability, it depends only weakly on the perturbation wavelength. Such instabilities may initiate star for mation near the boundaries of molecular clouds in the ISM on timescale s of similar to 10(6)-10(7) yr.