What constraints on the neutron star maximum mass can one pose from GW170817 observations?

TL;DR

This paper uses gravitational wave data from GW170817 and universal relations of neutron stars to constrain the maximum mass of non-spinning neutron stars, considering different post-merger scenarios and their implications.

Contribution

It provides new bounds on the neutron star maximum mass based on GW170817, incorporating universal relations and exploring various post-merger neutron star states.

Findings

Maximum neutron star mass constrained to < 2.09 M_sun for black hole formation.

Allowed mass range for massive neutron stars extends up to ~2.43 M_sun.

Existence of parameter sets for magnetic field and ellipticity that allow long-lived supramassive neutron stars.

Abstract

The post-merger product of the first binary neutron star merger event detected in gravitational waves, GW170817, depends on neutron star equation of state (EoS) and is not well determined. We generally discuss the constraints one may pose on the maximum mass of a non-spinning neutron star, $M_{\rm TOV}$, based on the observations and some EoS-independent universal relations of rapidly-spinning neutron stars. If the merger product is a black hole after a brief hypermassive neutron star (HMNS) phase, we derive $M_{\rm TOV} < 2.09^{+0.11}_{-0.09}(^{+0.06}_{-0.04}) M_{\odot}$ at the 2$\sigma$ (1$\sigma$) level. The cases for a massive neutron star (MNS), either a supra-massive neutron star (SMNS) or even a stable neutron star (SNS), are also allowed by the data. We derive $2.09^{+0.11}_{-0.09}(^{+0.06}_{-0.04} M_{\odot}) \leq M_{\rm TOV}< 2.43^{+0.10}_{-0.08}(^{+0.06}_{-0.04}) M_{\odot}$ for the SMNS case and $M_{\rm TOV} \geq 2.43^{+0.10}_{-0.08}(^{+0.06}_{-0.04})M_{\odot}$ for the SNS case, at the $2\sigma$ ($1\sigma$) confidence level. In the MNS cases, we also discuss the constraints on the neutron star parameters (the dipolar magnetic field strength at the surface $B_p$ and the ellipticity $\epsilon$) that affect the spindown history, by considering different MNS survival times, e.g. 300 s, 1 d, and 155 d after the merger, as suggested by various observational arguments. We find that once an SMNS is formed, without violating the EM observational constraints, there always exist a set of ($B_p, \epsilon$) parameters that allow the SMNS to survive for 300s, 1 d, 155 d, or even longer.