The evolution of rotating stars. II - Calculations with time-dependent redistribution of angular momentum for 7- and 10-solar-mass stars

Abstract

Calculations have been performed for the evolution of rotating stars with realistic time-dependent redistribution of angular momentum and chemical composition due to gas-dynamical instabilities. Convection and Eddington circulation are found to be the most important mechanisms for changing the angular-momentum distribution, while the dynamical shear and Solberg-Hoiland instabilities produce chemical mixing in regions which remain unmixed in nonrotating calculations. The calculations indicate that ignoring the finite time scales associated with angular-momentum redistribution is a poor and often misleading approximation. The primary results are: (1) evolved stellar cores develop nonaxisymmetric instabilities corresponding to the bifurcation of the Maclaurin sequence before they reach critical (Keplerian) rotational velocities; (2) for the 7-solar-mass star, the instability point is reached prior to carbon ignition, indicating that catastrophic carbon detonation may be avoided by rotating stars; and (3) the hydrodynamic events associated with violent stellar death will generally involve rapidly rotating, triaxial, or fissioning cores. In addition to radically altering the nature of these events, this indicates that stellar collapse may be a strong source of gravitational-wave radiation.