GW170817 and GW190814: tension on the maximum mass

TL;DR

This paper analyzes constraints on the maximum neutron star mass from GW170817 and GW190814, finding a consistent value around 2.21 solar masses and discussing implications of the tension between observations.

Contribution

It employs a genetic algorithm to reconcile observational data, providing refined estimates of the maximum neutron star mass and exploring the implications of the secondary object in GW190814.

Findings

Maximum neutron star mass estimated at ~2.21 M_sun

Masses above 2.5 M_sun conflict with gravitational-wave emission efficiencies

Tension can be alleviated if the GW190814 secondary was a black hole

Abstract

The detection of the binary events GW170817 and GW190814 has provided invaluable constraints on the maximum mass of nonrotating configurations of neutron stars, $M_{_{\rm TOV}}$. However, the large differences in the neutron-star masses measured in GW170817 and GW190814 has also lead to a significant tension between the predictions for such maximum masses, with GW170817 suggesting that $M_{_{\rm TOV}} \lesssim 2.3\,M_{\odot}$, and GW190814 requiring $M_{_{\rm TOV}} \gtrsim 2.5\,M_{\odot}$ if the secondary was a (non- or slowly rotating) neutron star at merger. Using a genetic algorithm, we sample the multidimensional space of parameters spanned by gravitational-wave and astronomical observations associated with GW170817. Consistent with previous estimates, we find that all of the physical quantities are in agreement with the observations if the maximum mass is in the range $M_{_{\rm TOV}} = 2.210^{+0.116}_{-0.123} \,M_{\odot}$ within a $2\textrm{-}\sigma$ confidence level. By contrast, maximum masses with $M_{_{\rm TOV}} \gtrsim 2.5\,M_{\odot}$, not only require efficiencies in the gravitational-wave emission that are well above the numerical-relativity estimates, but they also lead to a significant under-production of the ejected mass. Hence, the tension can be released by assuming that the secondary in GW190814 was a black hole at merger, although it could have been a rotating neutron star before.