# Are merging black holes born from stellar collapse or previous mergers?

## TL;DR

This paper investigates whether gravitational-wave data can distinguish black hole mergers originating from stellar collapse versus those from previous mergers, using Bayesian analysis of population models and observed parameters.

## Contribution

It introduces a Bayesian model selection method to differentiate black hole formation scenarios based on gravitational-wave observations of mass, spin, and redshift.

## Key findings

- Bayesian analysis can effectively distinguish formation scenarios
- Mass and spin distributions differ between first and second-generation black holes
- Observations can identify the formation history of merging black holes

## Abstract

Advanced LIGO detectors at Hanford and Livingston made two confirmed and one marginal detection of binary black holes during their first observing run. The first event, GW150914, was from the merger of two black holes much heavier that those whose masses have been estimated so far, indicating a formation scenario that might differ from "ordinary" stellar evolution. One possibility is that these heavy black holes resulted from a previous merger. When the progenitors of a black hole binary merger result from previous mergers, they should (on average) merge later, be more massive, and have spin magnitudes clustered around a dimensionless spin ~0.7. Here we ask the following question: can gravitational-wave observations determine whether merging black holes were born from the collapse of massive stars ("first generation"), rather than being the end product of earlier mergers ("second generation")? We construct simple, observationally motivated populations of black hole binaries, and we use Bayesian model selection to show that measurements of the masses, luminosity distance (or redshift), and "effective spin" of black hole binaries can indeed distinguish between these different formation scenarios.