Spin-Orbit Resonance and the Evolution of Compact Binary Systems

Starting with a post-Newtonian description of compact binary systems, we derive a set of equations that describes the evolution of the orbital angular momentum and both spin vectors during inspiral. We find regions of phase space that exhibit resonance behavior, characterized by small librations of the spin vectors around a fixed orientation. Due to the loss of energy and orbital angular momentum through radiation reaction, systems can eventually be captured into these resonance orientations. By investigating the long-term evolution of compact binaries with a variety of initial conditions, we find that the distribution in parameter space can be strongly affected by resonance captures. This has the effect of significantly reducing the size of search space for gravitational wave sources, in turn improving the chances of detecting such sources through methods of template matching. Furthermore, by calculating the expected spin distribution at the end of the inspiral phase, we can predict what are the most likely initial conditions for the plunge phase, a result of great interest for numerical relativity calculations.