Estimating the maximum gravitational mass of nonrotating neutron stars from the GW170817/GRB 170817A/AT2017gfo observation

TL;DR

This paper derives an analytical expression to estimate the maximum gravitational mass of nonrotating neutron stars using GW170817 observations, providing a new method to constrain neutron star properties.

Contribution

The work introduces an EoS-insensitive analytical formula for the critical mass of supramassive neutron stars formed in mergers, linking it to observable quantities and constraining $M_{TOV}$.

Findings

Estimated $M_{TOV}$ as 2.13 solar masses from GW data.

Derived an EoS-insensitive expression for supramassive NS mass.

Confirmed consistency with current neutron star mass measurements.

Abstract

Assuming that the differential rotation of the massive neutron star (NS) formed in the double NS (DNS) mergers has been effectively terminated by the magnetic braking and a uniform rotation has been subsequently established (i.e., a supramassive NS is formed), we analytically derive in this work an approximated expression for the critical total gravitational mass ($M_{\rm tot,c}$) to form supramassive NS (SMNS) in the DNS mergers, benefited from some equation of state (EoS) insensitive relationships. The maximum gravitational mass of the nonrotating NSs ($M_{\rm TOV}$) as well as the dimensionless angular momentum of the remnant ($j$) play the dominant roles in modifying $M_{\rm tot,c}$, while the radius and mass differences of the premerger NSs do not. The GW170817/GRB 170817A/AT2017gfo observations have provided so far the best opportunity to quantitatively evaluate $M_{\rm TOV}$. Supposing the central engine for GRB 170817A is a black hole quickly formed in the collapse of an SMNS, we find $M_{\rm TOV}=2.13^{+0.09}_{-0.08}M_\odot$ (68.3% credibility interval, including also the uncertainties of the EoS insensitive relationships), which is consistent with the constraints set by current NS mass measurements.