# Gravitational-wave sources from mergers of binary black-holes catalyzed by fly-bys interactions in the field

## TL;DR

This paper introduces a new mechanism for black hole binary mergers driven by stellar fly-bys that excite eccentricities in wide binaries, leading to gravitational-wave emissions, with a rate comparable to observations.

## Contribution

It presents an analytic model for wide binary black hole mergers catalyzed by stellar fly-bys, a novel formation channel supported by numerical verification.

## Key findings

- Merger rate estimated at ~10 times the fraction of wide binaries per Gpc^3 per year.
- Predicted observational signatures include spin-orbit misalignment and high mass-ratio preferences.
- The model's merger rate aligns with current observational estimates.

## Abstract

Several scenarios were suggested for the origins of gravitational-wave (GW) sources from mergers of stellar binary black holes (BBHs). Here we propose a novel origin through catalyzed formation of GW-sources from ultra-wide binaries in the field. Such binaries experience perturbations from random stellar fly-bys which excite their eccentricities. Once a wide-binary is driven to a sufficiently small peri-center approach, GW-emission becomes significant, and the binary inspirals and merges. We derive an analytic model and verify it with numerical calculation to compute the merger rate to be $\sim10{\rm \times f_{wide}\,{\rm Gpc}^{-3}yr^{-1}}$ ($f_{{\rm wide}}$ is the fraction of wide BH-binaries), which is comparable to the observationally inferred rate. The observational signatures from this channel include spin-orbit misalignment; preference for high mass-ratio BBH; preference for high velocity-dispersion host-galaxies; and a uniform delay-time distribution.