Self‐gravity driven instabilities of interfaces in the interstellar medium

In order to understand star formation it is important to understand the dynamics of atomic and molecular clouds in the interstellar medium (ISM). Non‐linear hydrodynamic flows are a key component to the ISM. One route by which non‐linear flows arise is the onset and evolution of interfacial instabilities. Interfacial instabilities act to modify the interface between gas components at different densities and temperatures. Such an interface may be subject to a host of instabilities, including the Rayleigh–Taylor, Kelvin–Helmholtz, and Richtmyer–Meshkov instabilities. Recently, a new density interface instability was identified. This self‐gravity interfacial instability (SGI) causes any displacement of the interface to grow on roughly a free‐fall time‐scale, even when the perturbation wavelength is much less than the Jeans length. In previous work, we used numerical simulations to confirm the expectations of linear theory and examine the non‐linear evolution of the SGI. We now continue our study by generalizing our initial conditions to allow the acceleration due to self‐gravity to be non‐zero across the interface. We also consider the behaviour of the SGI for perturbation wavelengths near the Jeans wavelength. We conclude that the action of self‐gravity across a density interface may play a significant role in the ISM either by fuelling the growth of new instabilities or modifying the evolution of existing instabilities.