Instability of the stochastic galactic magnetic field

We examine the effects of the stochastic galactic magnetic field on the dynamical instability of the interstellar gas and magnetic field. The large-scale random walk, or meandering, of the magnetic field exerts stresses across the average magnetic field direction, which suppress the growth of perturbations having a small wavelength normal to the field. The result is that, compared with a nonstochastic initial magnetic field, those perturbations, which grow, are significantly broadened in the direction normal to the field. Hence, the instability in a stochastic magnetic field, such as that observed in our Galaxy, should evolve into clouds that are more similar to those that are observed than are those found in the absence of the stochastic field.