On the nature of GW190814 and its impact on the understanding of supranuclear matter

TL;DR

This paper analyzes the GW190814 event to determine whether the secondary object was a neutron star or black hole, concluding it was almost certainly a binary black hole, and discusses implications for the nuclear equation of state.

Contribution

The study applies a nuclear-physics-multimessenger framework to assess the nature of GW190814 and explores its impact on understanding supranuclear matter and neutron star properties.

Findings

GW190814 is >99.9% likely a binary black hole merger.

Even with relaxed constraints, the probability remains ~81% for a black hole origin.

A neutron star scenario would require very stiff equations of state with high maximum sound speed.

Abstract

The observation of a compact object with a mass of $2.50-2.67M_{\odot}$ on August 14, 2019, by the LIGO Scientific and Virgo collaborations (LVC) has the potential to improve our understanding of the supranuclear equation of state. While the gravitational-wave analysis of the LVC suggests that GW190814 likely was a binary black hole system, the secondary component could also have been the heaviest neutron star observed to date. We use our previously derived nuclear-physics-multimessenger astrophysics framework to address the nature of this object. Based on our findings, we determine GW190814 to be a binary black hole merger with a probability of $>99.9\%$. Even if we weaken previously employed constraints on the maximum mass of neutron stars, the probability of a binary black hole origin is still $\sim 81\%$. Furthermore, we study the impact that this observation has on our understanding of the nuclear equation of state by analyzing the allowed region in the mass-radius diagram of neutron stars for both a binary black hole or neutron star--black hole scenario. We find that the unlikely scenario in which the secondary object was a neutron star requires rather stiff equations of state with a maximum speed of sound $c_s\geq \sqrt{0.6}$ times the speed of light, while the binary black hole scenario does not offer any new insight.