# Binary black hole mergers from field triples: properties, rates and the impact of stellar evolution

## TL;DR

This paper models the formation of binary black hole mergers from field triple stars, highlighting their unique properties, merger rates, and high eccentricities, which can help distinguish their origins in gravitational wave observations.

## Contribution

It introduces a self-consistent simulation of massive triple star evolution combining secular dynamics and stellar evolution, revealing the impact on black hole merger properties and rates.

## Key findings

- Merger rate estimated at 0.3-1.3 Gpc^{-3}yr^{-1}
- Black hole mergers from triples exhibit higher eccentricities than other channels
- Potential detection of up to 10 events per year with Advanced-LIGO

## Abstract

We consider the formation of binary black hole mergers through the evolution of field massive triple stars. In this scenario, favorable conditions for the inspiral of a black hole binary are initiated by its gravitational interaction with a distant companion, rather than by a common-envelope phase invoked in standard binary evolution models. We use a code that follows self-consistently the evolution of massive triple stars, combining the secular triple dynamics (Lidov-Kozai cycles) with stellar evolution. After a black hole triple is formed, its dynamical evolution is computed using either the orbit-averaged equations of motion, or a high-precision direct integrator for triples with weaker hierarchies for which the secular perturbation theory breaks down. Most black hole mergers in our models are produced in the latter non-secular dynamical regime. We derive the properties of the merging binaries and compute a black hole merger rate in the range (0.3- 1.3) Gpc^{-3}yr^{-1}, or up to ~2.5Gpc^{-3}yr^{-1} if the black hole orbital planes have initially random orientation. Finally, we show that black hole mergers from the triple channel have significantly higher eccentricities than those formed through the evolution of massive binaries or in dense star clusters. Measured eccentricities could therefore be used to uniquely identify binary mergers formed through the evolution of triple stars. While our results suggest up to ~10 detections per year with Advanced-LIGO, the high eccentricities could render the merging binaries harder to detect with planned space based interferometers such as LISA.