Mechanism for inducing synchronous rotation and small eccentricity in close binary systems

Abstract

Rotation through a tidal bulge generates a fluid shear which, in stars, implies a very high Reynolds number; fully developed turbulence might result. Turbulent viscosities, synchronization, and circularization time scales are computed. The calculation contains no adjustable dimensional parameters. It explains the observed fact of synchronous rotation for orbital periods not exceeding about 4 days and of nonsynchronous rotation for larger periods. The observed small eccentricity of some short-period binary X-ray sources is also an immediate consequence.