Convective and rotational stability of a dilute plasma

The stability of a dilute plasma to local convective and rotational disturb ances is examined. A subthermal magnetic field and finite thermal conductiv ity along the field lines are included in the analysis. Stability criteria similar in form to the classical inequalities are found, but with angular v elocity Hoiland gradients replacing angular momentum gradients, and tempera ture gradients replacing entropy gradients. These criteria are indifferent to the properties of the magnetic field and to the magnitude of the thermal conductivity. Angular velocity gradients and temperature gradients are bot h free energy sources; it is not surprising that they are directly relevant to the stability of the gas. Magnetic fields and thermal conductivity prov ide the means by which these sources can be tapped. Previous studies have g enerally been based upon the classical criteria, which are inappropriate fo r magnetized, dilute astrophysical Hoiland plasmas. In sharp contrast to re cent claims in the literature, the new stability criteria demonstrate that marginal flow stability is not a fundamental property of accreting plasmas thought to be associated with low-luminosity X-ray sources.