Evolution of Binaries in Dense Stellar Systems

In contrast to the field, the binaries in dense stellar systems are frequently not primordial, and could be either dynamically formed or significantly altered from their primordial states. Destruction and formation of binaries occur in parallel all the time. The destruction, which constantly removes soft binaries from a binary pool, works as an energy sink and could be a reason for a cluster to enter the binary-burning phase. The true binary fraction is greater than observed, as a result, the observable binary fraction evolves differently from the predictions. Combined measurements of binary fractions in globular clusters suggest that most of the clusters are still core-contracting. The formation, on other hand, affects the more evolutionary advanced stars most, which significantly enhances the population of X-ray sources in globular clusters. The formation of binaries with a compact object proceeds mainly through physical collisions, binary-binary and single-binary encounters; however, it is the dynamical formation of triples and multiple encounters that principally determines whether the formed binary will become an X-ray source.