Radius and equation of state constraints from massive neutron stars and GW190814

Motivated by the unknown nature of the 2.50-2.67 M-circle dot compact object in the binary merger event GW190814, we study the maximum neutron star mass based on constraints from low-energy nuclear physics, neutron star tidal deformabilities from GW170817, and simultaneous mass-radius measurements of PSR J0030+045 from NICER. Our prior distribution is based on a combination of nuclear modeling valid in the vicinity of normal nuclear densities together with the assumption of a maximally stiff equation of state at high densities, a choice that enables us to probe the connection between observed heavy neutron stars and the transition density at which conventional nuclear physics models must break down. We demonstrate that a modification of the highly uncertain suprasaturation density equation of state beyond 2.64 times normal nuclear density is required in order for chiral effective field theory models to be consistent with current neutron star observations and the existence of 2.6M(circle dot) neutron stars. We also show that the existence of very massive neutron stars strongly impacts the radii of approximate to 2.0M(circle dot) neutron stars (but not necessarily the radii of 1.4M(circle dot) neutron stars), which further motivates future NICER radius measurements of PSR J1614-2230 and PSR J0740+6620.

Automated summary

The study investigates the nature of an unknown compact object in a binary merger event and determines the maximum neutron star mass based on constraints from various physics models. It is shown that modifications to high-density equations of state are necessary to reconcile theoretical models with current neutron star observations. Furthermore, the existence of very massive neutron stars has a significant impact on the radii of other neutron stars, prompting further research in the field.