# Determining the population properties of spinning black holes

## TL;DR

This paper introduces a framework to analyze gravitational-wave data to infer the population properties and formation scenarios of spinning black holes, distinguishing between different astrophysical models based on observed spin orientations.

## Contribution

It develops a minimal-assumption, data-driven method to constrain black hole spin population hyperparameters from gravitational-wave observations.

## Key findings

- Constraints on black hole spin misalignment distributions.
- Evidence for multiple black hole merger populations.
- Method to test formation scenarios using spin data.

## Abstract

There are at least two formation scenarios consistent with the first gravitational-wave observations of binary black hole mergers. In field models, black hole binaries are formed from stellar binaries that may undergo common envelope evolution. In dynamic models, black hole binaries are formed through capture events in globular clusters. Both classes of models are subject to significant theoretical uncertainties. Nonetheless, the conventional wisdom holds that the distribution of spin orientations of dynamically merging black holes is nearly isotropic while field-model black holes prefer to spin in alignment with the orbital angular momentum. We present a framework in which observations of black hole mergers can be used to measure ensemble properties of black hole spin such as the typical black hole spin misalignment. We show how to obtain constraints on population hyperparameters using minimal assumptions so that the results are not strongly dependent on the uncertain physics of formation models. These data-driven constraints will facilitate tests of theoretical models and help determine the formation history of binary black holes using information encoded in their observed spins. We demonstrate that the ensemble properties of binary detections can be used to search for and characterize the properties of two distinct populations of black hole mergers.