Quasi-stationary tidal evolution with arbitrarily misaligned orbital and stellar angular momenta with a preliminary numerical investigation in the non-dissipative limit

TL;DR

This paper develops first-principles equations for the tidal evolution of misaligned binary systems, revealing phenomena like inclination flips, libration, and eccentricity variations, even without dissipation, with potential observational implications.

Contribution

It introduces a novel set of evolution equations derived from first principles that include all relevant precession effects and applies them to study complex dynamical behaviors.

Findings

Periodic inclination and precession rate changes observed.

Possibility of flips between prograde and retrograde rotation.

Significant eccentricity variations when spin exceeds orbital angular momentum.

Abstract

(Abbreviated) We extend the results of our 2021 paper concerning the problem of tidal evolution of a binary system with a rotating primary component with rotation axis arbitrarily inclined with respect to the orbital plane. Only the contribution of quasi-stationary tides is discussed. Unlike previous studies in this field we present evolution equations derived 'from first principles'. The governing equations contain two groups of terms. The first group of terms determines the evolution of orbital parameters and inclination angles a 'viscous' time scale. The second group of terms is due to stellar rotation. These terms are present even when dissipation in the star is neglected. Unlike in our 2021 paper we consider all potentially important sources of apsidal precession in an isolated binary, namely precession arising from the tidal distortion and rotation of the primary as well as Einstein precession. We solve these equations numerically for a sample of input parameters, leaving a complete analysis to an accompanying paper. Periodic changes to both the inclination of the rotational axis and its precession rate are found. For a particular binary parameters periodic flips between prograde and retrograde rotation are possible. Also, when the inclination angle is allowed to vary, libration of the apsidal angle becomes possible. Furthermore, when the spin angular momentum is larger than the orbital angular momentum there is a possibility of a significant periodic eccentricity changes. These phenomena could, in principle, be observed in systems with relatively large inclinations and eccentricities such as e.g. those containing a compact object. In such systems both large inclinations and eccentricities could be generated as a result of a kick applied to the compact object during a supernova explosion.