High eccentricities and high masses characterize gravitational-wave captures in galactic nuclei as seen by Earth-based detectors

The emission of gravitational waves (GWs) during single-single close encounters in galactic nuclei (GNs) leads to the formation and rapid merger highly eccentric stellar-mass black hole (BH) binaries. distinct distribution physical parameters makes it possible statistically distinguish this source population from others. Previous studies determined expected binary parameter for single GNs. Here we take into account effects dynamical friction, post-Newtonian corrections, observational bias determine detected sources' parameter-distributions all GNs Universe. We find that total mass mergers is strongly tilted towards higher masses. initial peak GW frequency remarkably high between 1-70 Hz, ~50% capture sources form above 10 Hz with e >~ 0.95. eccentricity when first entering LIGO/Virgo/KAGRA band satisfies e_10Hz > 0.1 over 92% 0.8 more than half sources. At point pericenter reaches GM/c^2 e_10M ~70% sources, making events most among currently known BH channels identify correlations mass, ratio, detection distance, eccentricities e_10M. recently measured GW190521 lie theoretical distributions estimated escape speed host environment ~7.5x10^3 km/s - 1.2x10^4 km/s, a candidate astrophysical channel.