Thermal instability in the presence of the cosmic ray and ambipolar diffusion

Abstract

ABSTRACT The aim of this study is to investigate the impact of the cosmic ray (CR) and ambipolar diffusion (AD) on the thermal instability in a weakly ionized gas. The CR propagates along the magnetic-field line, where the AD is present. The weakly ionized gas and the CR are considered as two different interacting fluids. Using the linear perturbation analysis, we consider the occurrence of the thermal instability to obtain a dispersion relation in the presence of both phenomena. This equation describes the stable and unstable modes in the terms of some parameters, which depend on the CR and AD. The results show that the angle between the direction of the perturbation propagation and the magnetic-field lines plays an important role on the domains of stability and instability. Furthermore, we found that there is a characteristic wavelength related to the ambipolar diffusivity that explains whether the AD increases the magnetic support of the cloud against the collapse, or decreases it against the collapse. Finally, the results address some new points in the study of the structure formation within the clumpy molecular clouds, as well as the formation of the low-mass stars in the interstellar medium.