Stellar tides

Abstract

To a first approximation, a binary star behaves as a closed system; therefore it conserves its angular momentum while evolving to its state of minimum kinetic energy, where the orbits are circular, all spins are aligned, and the components rotate in synchronism with the orbital motion. The pace at which this final state is reached depends on the physical processes responsible for the dissipation of the tidal kinetic energy. For stars with an outer convection zone, the dominant mechanism is presumably the turbulent dissipation acting on the equilibrium tide. For stars with an outer radiation zone, the major dissipative process is radiative damping operating on the dynamical tide. I shall review these physical processes, discuss uncertainties in their present treatment, describe the latest developments, and compare the theoretical predictions with the observed properties concerning the orbital circularization of close binaries. © Springer-Verlag 2013.