Speaker
Description
There is growing evidence that a substantial fraction of the compact object mergers detected through gravitational waves merge with non-zero eccentricity or large spin-orbit misalignment. In particular, recent evidence for an eccentric neutron star-black hole (NSBH) merger and NSBHs with anti-aligned BH spins challenge leading formation scenarios to date. Residual eccentricity rules out formation through isolated binary star evolution, while neutron star natal kicks and the unequal masses of NSBHs inhibit efficient pairing in dense stellar environments. I will show that all observed properties---NSBH merger rate, eccentricity, and spin-orbit misalignment---are explained by the high prevalence of massive stellar triples in the field. I will discuss that the formation of the neutron star (its natal kick and the mass-loss in supernova, often reduced via binary envelope stripping) decisively impacts the triple stability, preferentially leaving behind surviving NSBHs in compact triple architectures.
The rich three-body dynamics of compact, unequal-mass triples enables mergers across a wide range of orbital parameters without requiring fine-tuned highly inclined tertiary orbits and provides a natural explanation for an abundance of residual eccentricity and spin-orbit misalignment. Finally, I will discuss how spin measurements from future eccentric binary black hole mergers could provide key insights into their formation pathways.