Compact Binary Merger Rates: Comparison with LIGO/Virgo Upper Limits

TL;DR

This paper compares predicted binary merger rates with LIGO/Virgo observational limits, highlighting the impact of detector sensitivity, stellar evolution models, and black hole natal kicks on detection prospects.

Contribution

It provides updated predictions of merger rates, assesses the effects of black hole natal kicks, and discusses detection potential with advanced gravitational wave detectors.

Findings

Optimistic models are 18 times below initial LIGO/Virgo limits for BH-BH.

Modest sensitivity increase could lead to first detections.

Massive BH-BH mergers detectable up to redshift z=2.

Abstract

We compare evolutionary predictions of double compact object merger rate densities with initial and forthcoming LIGO/Virgo upper limits. We find that: (i) Due to the cosmological reach of advanced detectors, current conversion methods of population synthesis predictions into merger rate densities are insufficient. (ii) Our optimistic models are a factor of 18 below the initial LIGO/Virgo upper limits for BH-BH systems, indicating that a modest increase in observational sensitivity (by a factor of 2.5) may bring the first detections or first gravitational wave constraints on binary evolution. (iii) Stellar-origin massive BH-BH mergers should dominate event rates in advanced LIGO/Virgo and can be detected out to redshift z=2 with templates including inspiral, merger, and ringdown. Normal stars (<150 Msun) can produce such mergers with total redshifted mass up to 400 Msun. (iv) High black hole natal kicks can severely limit the formation of massive BH-BH systems (both in isolated binary and in dynamical dense cluster evolution), and thus would eliminate detection of these systems even at full advanced LIGO/Virgo sensitivity. We find that low and high black hole natal kicks are allowed by current observational electromagnetic constraints. (v) The majority of our models yield detections of all types of mergers (NS-NS, BH-NS, BH-BH) with advanced detectors. Numerous massive BH-BH merger detections will indicate small (if any) natal kicks for massive BHs.