Rayleigh Taylor instabilities in the interstellar medium

The authors describe a new approach to the problem of instabilities in the interstellar medium and try to answer the questions which remained open from previous proposals. In this perspective, they built a tool to test the stability of any 2 dimensional equilibrium configurations able to represent the interstellar medium. They adapted the energy principle used by Bernstein et al. (1958) to test hydromagnetic configurations. They developed it for the composite interstellar medium made of interstellar gas and cosmic rays gas, immersed in the galactic magnetic field and in the gravitational field of the galactic stars. (Auth.)