Local Dynamic Thermal Instability
Abstract
A very simple but general criterion for local thermal instability in dynamical sytems is derived. The background flow may be timedependent. The instability criterion is very similar to the classical Field result, except that the cooling function L is replace by L/T, whre T is the temperature. Previous results in the literature are special cases of our result. A thirdorder differential equation for the evolution of smallwavelength radial perturbations in spherical systems is derived. With selfgravity, it is the exact equation that would result for the evolution of perturbations in simple matterdominated Friedmann cosmologies (or any homogeneous volume change) subject to external heating and cooling. The scale factor is determined by the unperturbed velocity flow. The equation is solved by WKBJ techniques, allowing acoustical and condensational modes to be treated on an equal footing. Transport processes are not considered here. Selfgravity and fragmentation are briefly discussed.
 Publication:

The Astrophysical Journal
 Pub Date:
 April 1986
 DOI:
 10.1086/184657
 Bibcode:
 1986ApJ...303L..79B
 Keywords:

 Astrophysics;
 Hydrodynamics;
 Thermal Instability;
 Flow Equations;
 Gravitation;
 Perturbation Theory;
 Time Dependence;
 Astrophysics;
 HYDRODYNAMICS;
 INSTABILITIES