Instability in Massive Stars: An Overview

Abstract

Dynamical, vibrational, and thermal instabilities of massive blue stars are discussed as possible mechanisms for the observed brightness variations of such objects. Relaxation oscillations (on local thermal time scales) due to dynamical instabilities of the stellar wind flows appear to be the most likely mechanism, at least for the S Dor variables. Very massive main-sequence stars with M > 10³ M_⊙ should be violently vibrationally unstable and therefore should differ significantly from stable main-sequence stars of lower mass.