Search for eccentric NSBH and BNS mergers in the third observing run of Advanced LIGO and Virgo

Abstract

The possible formation histories of neutron star binaries remain unresolved by current gravitational-wave catalogs. The detection of an eccentric binary system could be vital in constraining compact binary formation models. We present the first search for aligned spin eccentric neutron star-black hole binaries (NSBH) and the most sensitive search for aligned-spin eccentric binary neutron star (BNS) systems using data from the third observing run of the advanced LIGO and advanced Virgo detectors. No new statistically significant candidates are found; we constrain the local merger rate for specific astrophysical models to be less than 150Gpc−3yr−1 for binary neutron stars in the field, and, 50, 100, and 70 Gpc−3 yr−1 for neutron star-black hole binaries in globular clusters, hierarchical triples and nuclear clusters, respectively, at the 90% confidence level if we assume that no sources have been observed from these populations. We predict the capabilities of upcoming and next-generation observatory networks; we investigate the ability of three LIGO (A#) detectors and Cosmic Explorer CE (20 km)+CE (40 km) to use eccentric binary observations for determining the formation history of neutron star binaries. We find that 2–100 years of observation with three A# observatories are required before we observe clearly eccentric NSBH binaries; this reduces to only 10 days–1 year with the CE detector network. CE will observe tens to hundreds of measurably eccentric binaries from each of the formation models we consider. Published by the American Physical Society 2025