Many astrophysical objects result from the gravitational collapse of gaseous objects (for example, star formation occurs when molecular clouds collapse under gravity), and thus the stability of gaseous systems is of great interest. In general, a physical system is 'stable' if: 1) It is in equilibrium (there is a balance of forces such that the system is static), and 2) small deviations from equilibrium will tend to damp out, so that the system tends to return to equilibrium.