JEANS STABILITY OF DUSTY SPACE PLASMAS

The Jeans stability of dusty plasmas is re-considered. In contrast to a gas, a dusty plasma can support a plethora of wave modes each potent ially able to impart to the dust particles the randomising energy nece ssary to avoid Jeans collapse on some length scale, Consequently, the analysis of the stability to Jeans collapse is many-fold more complex in a dusty plasma than it is for a charge-neutral gas. After recalling some of the fundamental ideas related to the ordinary Jeans instabili ty in neutral gases, we extend the discussion to plasmas containing ch arged dust grains, Besides the usual Jeans criterion based upon therma l agitation, we consider two other ways of countering the gravitationa l collapse: (i) via the excitation of dust-acoustic modes and (ii) via a novel Alfven-Jeans instability, where perturbations of the dust mas s-loaded magnetic field counter the effects of self-gravitation. These two mechanisms yield different minimum threshold length scales for th e onset of instability/condensation. It is pointed out that for the st udy of the Jeans instability produced by density enhancements induced in the plasma by the presence of normal wave modes, even more prohibit ive plasma size constraints must necessarily be satisfied. (C) 1998 Pu blished by Elsevier Science B.V.