Occurrence of thermal instability in molecular clouds

Abstract

Linear perturbation is used on the complete MHD equations of the magnetic molecular clouds. We carry out a comparison of characteristic time-scales, and find conditions which linear thermal instability causes to form the small-scale condensations in the local expanding/contracting medium of a molecular cloud. We consider the ambipolar diffusion, or ion-neutral friction on the perturbed states. In this way, we obtain a non-dimensional characteristic equation that reduces to the prior characteristic equation in the non-gravitating stationary background. By manipulation of this characteristic equation, we conclude that there are, not only oblate formation regions, but also prolate condensation forming solutions, according to expansion or contraction of the background. Some typical data that correspond to the real observed magnetic molecular clouds is presented