# Gravitational Radiation Assisted Capture

## TL;DR

This paper demonstrates that gravitational radiation can cause two initially unbound bodies to become bound and eventually merge, significantly increasing the likelihood of such events compared to direct capture, with implications for black hole mergers.

## Contribution

It introduces the concept of gravitational radiation assisted capture, showing it has a much larger cross-section than direct capture for forming bound black hole pairs.

## Key findings

- Capture cross-section scales as (c/v_infinity)^{18/7}
- Captured bodies typically inspiral and merge within years
- Implications for black hole mergers in galaxies

## Abstract

It is shown that gravitational radiation can bind two initially unbound bodies; no third body is needed. Such captured bodies will almost always inspiral and merge due to further gravitational radiation on cosmologically negligible time scales (e.g., @ 5 years for GW150914). The capture cross-section $\sigma$ for such "capture and inspiraling" is far larger, for initial relative speed of the two objects $v_\infty\ll c$, than that $\sigma_{d}$ for "direct capture": $\sigma\propto\left(c / v_\infty\right)^{18/7}$, while $\sigma_{d}\propto\left(c / v_\infty\right)^2$. Implications of these results for black hole binary mergers, and giant black holes at galactic centers, are discussed.