Title: Can hierarchical triples explain LIGO–Virgo mergers?
Abstract: The recent discovery of gravitational waves has opened new horizons. Current and upcoming missions promise to shed light on black holes (BHs) of every size and neutron star (NS) physics. The astrophysical origin of these mergers is among the most puzzling open questions of our time. Two primary channels have been proposed to explain the observed population of merging BHs and NSs: field binary evolution and dynamical formation in a cluster environment. The LIGO–Virgo events have made possible to estimate rates, masses, eccentricities, and projected spins of merging compact objects for the fist time. However, neither field binary evolution nor dynamical formation can explain all of the above quantities. Observations show that about one fourth of massive stars is in triple systems, comprised of an inner binary orbited by a third companion. Despite being rarer than binaries, a large fraction of triples can merge as a result of the Kozai–Lidov mechanism, imposed on the inner binary by the field of the third companion. Within current uncertainties, triples can potentially account for most, if not all, of the observed events and future LIGO–Virgo sources. The triple scenario is definitively the third pathway to compact object mergers.