Equation-of-State Constraints on the Neutron-Star Binding Energy and Tests of Binary Formation Scenarios

TL;DR

This paper uses neutron star equation-of-state models and observations to constrain their binding energies, testing supernova progenitor scenarios and ruling out certain formation pathways for some neutron stars.

Contribution

It provides the first tight constraints on neutron star baryonic mass and binding energy to test binary formation models, especially electron-capture supernovae.

Findings

One neutron star likely did not form from an ONeMg core via electron-capture supernova.

Constraints on neutron star properties can differentiate binary formation scenarios.

Relations for baryonic mass and binding energy are derived using multi-messenger data.

Abstract

The second supernova that forms double-neutron-star systems is expected to occur in a progenitor that is ultra-stripped due to binary interactions. Thus, the secondary neutron star's mass as well as the post-supernova binary's orbital parameters will depend on the nature of the collapsing progenitor core. Since neutron stars are in the strong-gravity regime, their binding energy makes up a significant fraction of their total mass-energy budget. The second neutron star's binding energy may thus provide a unique insight as to whether its progenitor was a low-mass iron core or an oxygen-neon-magnesium core. I obtain relations for the baryonic mass and binding energy incorporating both a hadronic equation-of-state catalog as well as recent multi-messenger neutron-star observations. With these relations, I obtain the first tight constraints on the baryonic mass and binding energy of three neutron stars that are thought to have formed from an ultra-stripped progenitor. With these constraints, I test if each neutron star is consistent with forming from an ONeMg core that undergoes an electron-capture supernova. From these tests, I find that this scenario can be ruled out for one of three neutron stars. Neutron-star properties and the dense-matter equation of state can thus help distinguish binary formation scenarios.