Evolution of massive stars

Summary

Abstract

Recent results of the theory of massive star evolution are discussed. We divide the regime of massive stars in a “low” mass and a high mass part, and show that the evolution, the basic theoretical problems in their modeling, and the display of circuinstellar matter are quite different for stars from both parts.

For stars in the lower considered mass regime, it is shown that our ignorance about, internal mixing processes is the main source of uncertainty in stellar model calculations. Mixing processes related to thermal convection are discussed, and their effect on the observable stellar parameters and presupernova structure are sketched. The role of mixing induced by differential rotation is also briefly described. We argue that the supernova stage is a good possibility to investigate the circumstellar material of these objects and describe its high diagnostic potential for the whole presupernova evolution.

Our understanding of stars in the upper mass range, i.e. the most massive stars, also suffers from uncertainties related to internal mixing. However, we argue that it is the mass loss process which dominates their global evolution. The evidence that those objects do lose the major part of their initial mass before they collapse is discussed, together with the possibility of the display of circumstellar nebulae during their hydrostatic evolution. Finally, the fate of very massive stars is discussed.