A Common Origin for Low Mass Ratio Events Observed by LIGO and Virgo in the First Half of the Third Observing Run

TL;DR

This paper proposes a unified formation scenario for low mass ratio events observed by LIGO and Virgo, suggesting they originate from neutron star-black hole systems with a correlation between component masses, impacting population inferences.

Contribution

It introduces a common origin hypothesis for low mass ratio events, linking their formation to supernova ejecta dynamics and accretion processes in NSBH systems.

Findings

The secondary mass correlates with the primary black hole mass.

The proposed scenario explains the observed low mass ratio events.

Implications for distinguishing NSBH events from binary black hole populations.

Abstract

In its third observing run, the LIGO/Virgo collaboration has announced a potential neutron star-black hole (NSBH) merger candidate, GW190426_152155. Together with GW190814, these two events belong to a class of binaries with a secondary mass less than $3 \, M_{\odot}$. While the secondary system in GW190426_152155 is consistent with being a neutron star with a mass of $1.5^{+0.8}_{-0.5} \, M_{\odot}$, that of GW190814 is a $2.59^{+0.08}_{-0.09} \, M_{\odot}$ object and counts as the first confirmed detection of a mass-gap object. Here we argue that these two events could have a common origin as follows: both are formed as NSBH systems; however, the larger escape velocity of a system with more massive primary BH increases the bound fraction of the ejecta material from the supernova explosion leading to the formation of a NS. This bound material forms a disk, which is preferentially accreted onto the NS. This scenario predicts the secondary component mass should correlate with the primary component mass, which is consistent with GW190426_152155 and GW190814. If this hypothesis is corroborated by upcoming observations, GW190814-like events can be excluded from the binary black hole population when inferring their global characteristics.