Instabilities in a Nonuniform Partially Ionized Isothermal Magnetoplasma

Abstract

Electromagnetic modes and associated instabilities in a partially ionized, self-gravitating, nonuniform, isothermal, initially static magnetoplasma are theoretically investigated. The effects of the neutral fluid dynamics, the inhomogeneities in the external magnetic field and the background plasma number density, the self-gravitational field, the drag forces, the ionization and recombination, etc., on the dispersion properties of electromagnetic waves for different frequency regimes of interest are examined. It is shown that new types of instabilities, the first type of which is due to the combined effects of the self-gravitational and the drag forces, the second type of which is due to the combined effects of the plasma and the neutral fluid dynamics, and the third type of which is due to the drifting of electrons, exist in such a magnetoplasma. Furthermore, the effects of the external magnetic field and its inhomogeneity, the neutral fluid temperature, collisions of electrons or ions with neutrals, and the ionization play the stabilizing role, whereas the effects of the neutral fluid mass density, the plasma number density inhomogeneity, collisions of neutrals with electrons or ions, and the recombination play the destabilizing role. It is suggested that such instabilities could be responsible for the fragmentation of molecular clouds into substructures that in turn may fail to be supported against the self-gravity and may collapse to form the stars.