The Origin of Binary Black Holes Mergers

TL;DR

This paper analyzes LIGO-Virgo data to infer the origins of binary black hole mergers, suggesting field binaries are more likely than capture scenarios based on effective spin distributions, though current data is limited.

Contribution

It introduces a new statistical approach to distinguish between formation channels of black hole mergers using effective spin data.

Findings

Observed chi_{eff} distribution favors field binaries

Isotropic models are not ruled out with current data

Approximately a hundred observations needed for clear distinction

Abstract

Recently Venumadhav et al. (2019) proposed a new pipeline to analyze LIGO-Virgo's O1-O2 data and discovered eight new binary black hole (BBH) mergers, including a high effective spin, chi_{eff}, one. This discovery sheds new light on the origin of the observed BBHs and the dynamical capture vs. field binaries debate. Using a new statistical approach, we show that, while isotropic models are not ruled out, the observed chi_{eff} distribution favors field binaries, whose chi_{eff} is determined by tidal forces and wind losses, over capture. However, given the current limited sample size, capture scenarios (isotropic models) cannot be ruled out. Observations of roughly a hundred merges will enable us to distinguish between the different formation scenarios. However, if as expected, both formation channels operate it may be difficult to resolve their exact fraction.