Binary Evolution

Abstract

Stars in binary systems do not evolve in isolation. If the orbital separation is small enough, the tidal perturbations due to the companion can break the spherical symmetry that was assumed in the development of the evolution equations in Chap. 4 and then used in later chapters. For the most part, these additional considerations do not significantly alter the evolution of the components of a binary since the orbital periods are generally greater than dynamical timescales, yet much shorter than thermal timescales. However, if the stars begin to directly interact through mass transfer and mass loss, then the bulk properties of the components can change in mid-evolution, resulting in a dramatically different outcome in the evolution compared to isolated stars with the same properties. In this chapter, we will look at the physics of mass transfer and the consequences of mass transfer and mass loss on the evolution of the components of a binary as well as the binary system itself.