Forecasting the population properties of merging black holes

TL;DR

Third-generation gravitational-wave detectors will vastly improve our ability to analyze black hole populations, enabling precise measurements of their properties within months to decades, which is crucial for future astrophysical research.

Contribution

This paper introduces the first population-level Fisher-matrix forecasts tailored for third-generation gravitational-wave detectors, assessing their potential to constrain black hole population parameters.

Findings

Third-generation detectors will significantly improve constraints on black hole population hyperparameters.

A single detector and a network will have similar performance in population analysis.

Some population features can be measured within months, others require decades.

Abstract

Third-generation gravitational-wave detectors will observe up to millions of merging binary black holes. With such a vast dataset, stacking events into population analyses will arguably be more important than analyzing single sources. We present the first application of population-level Fisher-matrix forecasts tailored to third-generation gravitational-wave interferometers. We implement the formalism first derived by Gair et al. and explore how future experiments such as Einstein Telescope and Cosmic Explorer will constrain the distributions of black-hole masses, spins, and redshift. Third-generation detectors will be transformative, improving constraints on the population hyperparameters by several orders of magnitude compared to current data. At the same time, we highlight that a single third-generation observatory and a network of detectors will deliver qualitatively similar performances. Obtaining precise measurements of some population features (e.g. peaks in the mass spectrum) will require only a few months of observations while others (e.g. the fraction of binaries with aligned spins) will instead require years if not decades. We argue population forecasts of this kind should be featured in white papers and feasibility studies aimed at developing the science case of future gravitational-wave interferometers.