End-to-end study of the home and genealogy of the first binary neutron star merger

TL;DR

This study presents an end-to-end framework using stellar evolution simulations and spectral synthesis to analyze the first binary neutron star merger, GW170817, revealing details about its progenitor system and host galaxy.

Contribution

It introduces a comprehensive analysis framework combining different models to study neutron star merger progenitors and applies it to GW170817, improving understanding of their origins.

Findings

High probability (>98%) GW170817 originated from a Z=0.010 stellar population 5-12.5 Gyrs old.

Progenitor likely a binary with a 13-24 Msol primary and 10-12 Msol secondary.

Progenitors experienced two or three common envelope events.

Abstract

Binary neutron star mergers are one of the ultimate events of massive binary star evolution, and our understanding of their parent system is still in its infancy. Upcoming gravitational wave detections, coupled with multi-wavelength follow-up observations, will allow us to study an increasing number of these events by characterising their neighbouring stellar populations and searching for their progenitors. Stellar evolution simulations are essential to this work but they are also based on numerous assumptions. Additionally, the models used to study the host galaxies differ from those used to characterise the progenitors and are typically based on single star populations. Here we introduce a framework to perform an end-to-end analysis and deploy it to the first binary neutron star merger - GW170817. With the Binary Population And Spectral Synthesis (BPASS) codes we are able to retrieve the physical properties of the host galaxy NGC 4993 as well as infer progenitor candidates. In our simulations there is a >98% chance that GW170817 originated from a stellar population with Z=0.010 born between 5 and 12.5 Gyrs ago. By carefully weighing the stellar genealogies we find that GW170817 most likely came from a binary system born with a 13-24 Msol primary and 10-12 Msol secondary which underwent two or three common envelope events over their lifetime.