Formation and Evolution of Hierarchical Systems

Abstract

AbstractInitial distributions of primordial binaries used in realistic N-body simulations give rise to bound subsystems of different multiplicity. An examination of the formation process shows that the most compact triples arise via binary-binary collisions, whereas higher-order systems have diverse origins. Low formation rates are compensated by long life-times, leading to a significant population building up. Being fairly energetic, the outer orbit tends to shrink by further encounters. In addition, external perturbations also modify the eccentricity and may create conditions for instability. Onecharacteristic outcome is internal disruption by the sling-shot mechanism. Such interactions are often sufficiently energetic to produce high-velocityescapers and it is not uncommon for triples and quadruples to be ejected. For high inclinations, the eccentricity growth induced by the Kozai effect may lead to significant shrinkage of the inner binary orbit by tidal circularization. If some of the components were spit into a dynamically inactive ultra-hard binary, the hierarchies would be attributed an even higher multiplicity. One implication of these results is that a proportion of multiple systems observed in the field may have been formed in a dynamical environment.