Chaos and the Dynamical Evolution of Tidal Capture Binaries in Globular Clusters

Abstract

Globular clusters cores harbour many low-mass X-ray binaries, cataclysmic variables, and millisecond pulsar binaries which are likely to have been formed via the process of tidal capture. Tidal capture binaries were originally thought to be responsible for halting core collapse and for subsequent re-expansion via the process of ``binary heating''. The standard model, now suggests that these binaries are no longer viable as a direct energy source. We present the results of a study which suggests that tidal capture binaries may indeed be a significant direct source of energy for the cores of globular clusters. We show that following capture, these binaries go through a short, violent chaotic phase, with the orbital eccentricity (and hence the tidal energy) suffering large changes on a very short timescale. This is followed by a long quiescent phase in which the tidal energy remains small while the orbit circularizes only via normal dissipative effects. This quiescent phase allows captured main sequence stars to evolve in the absence of large tides, a fact important for the production of low-mass X-ray binaries and cataclysmic variables.