Dynamic Stability

Abstract

Processes underlying the stellar evolution are characterized by a wide variety of time scales, such as hydrodynamical (т _h ), thermal (т _th ) and nuclear (т _n ) times and a time characterizing the weak interaction rate (т _β ). Throughout most of the evolution, from the phase of the young contracting star to the late evolutionary phases, T _h remains the smallest of all the time scales. In massive presupernova models, under conditions of nuclear equilibrium, the time scale T _n is the smallest one (see Sect. 10.1). In an ordinary star there is a rough equilibrium with respect to rapid processes (static equilibrium, for example), while the evolutionary lifetime is determined by one of the slower processes, as follows