GW150914: Spin based constraints on the merger time of the progenitor system

TL;DR

This paper investigates how the low spin observed in GW150914 constrains the merger time and progenitor models of binary black hole systems, emphasizing the importance of spin measurements for understanding stellar evolution.

Contribution

It introduces a simple model linking observed black hole spin to the delay time in binary mergers, providing new constraints on progenitor scenarios based on spin data.

Findings

Lower limit for merger time: >10^8 years

Many proposed progenitor models are inconsistent with low observed spin

Spin observations can critically constrain stellar evolution models

Abstract

We explore the implications of the observed low spin of GW150914 within the context of stellar astrophysics and progenitor models. We conclude that many of the recently proposed scenarios are in marked tension with this observation. We derive a simple model for the observed spin in the case that the progenitor system was a field binary composed of a black hole (BH) and a Wolf-Rayet star and explore the implications of the observed spin for this model. The spin observation allows us to place a lower limit for the delay time between the formation of the BH+BH binary and the actual merger, $t_{\textrm{merge}}$. We use typical values for these systems to derive $t_{\textrm{merge}}\gtrsim10^{8}\,\textrm{yr}$, which proves to be an important diagnostic for different progenitor models. We anticipate the next series of events, and the associated spin parameters, will ultimately yield critical constraints on formation scenarios and on stellar parameters describing the late-stage evolution of massive stars.