Searching for Eccentricity: Signatures of Dynamical Formation in the First Gravitational-Wave Transient Catalogue of LIGO and Virgo

TL;DR

This study uses Bayesian inference with an eccentric waveform model to analyze LIGO and Virgo data, finding no significant eccentricity in observed binary black hole mergers, but setting upper limits that inform formation channel hypotheses.

Contribution

It introduces the application of the SEOBNRE eccentric waveform model to LIGO-Virgo data, providing the first constraints on binary black hole eccentricity in the catalog.

Findings

All observed events are consistent with zero eccentricity.

Upper limits on eccentricity range from 0.02 to 0.05 at 90% confidence.

Current limits do not strongly constrain the fraction of dynamical formation events.

Abstract

Binary black holes are thought to form primarily via two channels: isolated evolution and dynamical formation. The component masses, spins, and eccentricity of a binary black hole system provide clues to its formation history. We focus on eccentricity, which can be a signature of dynamical formation. Employing the spin-aligned eccentric waveform model SEOBNRE, we perform Bayesian inference to measure the eccentricity of binary black hole merger events in the first Gravitational-Wave Transient Catalogue of LIGO and Virgo. We find that all of these events are consistent with zero eccentricity. We set upper limits on eccentricity ranging from 0.02 to 0.05 with 90% confidence at a reference frequency of 10 Hz. These upper limits do not significantly constrain the fraction of LIGO-Virgo events formed dynamically in globular clusters, because only ~ 5% are expected to merge with measurable eccentricity. However, with the Gravitational-Wave Transient Catalogue set to expand dramatically over the coming months, it may soon be possible to significantly constrain the fraction of mergers taking place in globular clusters using eccentricity measurements.