Dusty Molecular Cloud Collapse in the Presence of Alfvén Waves

Abstract

It has been shown that magnetic fields play an important role in the stability of molecular clouds, mainly perpendicularly to the field direction. However, in the parallel direction the stability is a serious problem still to be explained. Interstellar turbulence may allow the generation of Alfvén waves that propagate through the clouds in the magnetic field direction. These regions also present great amounts of dust particles which can give rise to new wave modes, or modify the pre-existing ones. The dust-cyclotron damping affects the Alfvén wave propagation near the dust- cyclotron frequency. On the other hand, the clouds present different grain sizes, which carry different charges. In this sense, a dust particle distribution has several dust-cyclotron frequencies and it will affect a broad band of wave frequencies. In this case, the energy transfer to the gas is more efficient than in the case where the ion-cyclotron damping is considered alone. This effect becomes more important if a power law spectrum is considered for the wave energy flux, since the major part of the energy is concentrated in low-frequency waves. In this work we calculate the dust- cyclotron damping in a dusty and magnetized dwarf molecular cloud, as well as determine the changes in the Alfvén wave flux. Then, we use these results to study the gravitational stability of the cloud. We show that, considering the presence of charged dust particles, the wave flux is rapidly damped due to dust-cyclotron damping. Then the wave pressure acts in a small length scale, and cannot explain the observable cloud sizes, but can explain the existence of small and dense cores.