Effects of local cosmic inhomogeneities on the gravitational wave event rate

TL;DR

This paper investigates how local cosmic inhomogeneities, such as voids and clusters, bias the observed gravitational wave event rates, finding the effect to be at most 6% depending on detector sensitivity and binary properties.

Contribution

It provides the first quantitative estimate of how local matter distribution affects gravitational wave event rate measurements.

Findings

Local inhomogeneities can bias merger rate estimates by up to 6%.

The bias depends on the binary's chirp mass and detector sensitivity.

Inhomogeneity effects are suppressed by detector resolution and sensitivity limitations.

Abstract

The local universe is highly inhomogeneous and anisotropic. We live in a relatively sparse region of the Laniakea supercluster at the edge of a large 80 Mpc-wide void. We study the effect of these inhomogeneities on the measured gravitational wave event rates. In particular, we estimate how the measured merger rate of compact binaries is biased by the local matter distribution. The effect of the inhomogeneities on the merger rate is suppressed by the low angular resolution of gravitational wave detectors coupled with their smoothly decreasing population-averaged sensitivity with distance. We estimate the effect on the compact binary coalescence event rate to be at most 6% depending of the chirp mass of the target binary system and the sensitivity and orientation of the detectors.