Rotating Neutron Stars with the Relativistic Ab Initio Calculations

TL;DR

This paper develops relativistic equations of state for neutron stars using advanced ab initio calculations, analyzing their structural properties under rotation, and comparing predictions with astrophysical observations.

Contribution

It introduces a self-consistent relativistic Brueckner-Hartree-Fock approach for neutron star EOSs, incorporating negative-energy states, and explores rotational effects on neutron star structure.

Findings

Maximum rotating neutron star mass up to 2.93 solar masses.

Neutron star radius can extend to about 17 km for non-rotating 1.4 solar masses.

Predicted radius of PSR J0952-0607 less than 19.58 km.

Abstract

The equation of state (EOS) of extremely dense matter is crucial for understanding the properties of rotating neutron stars. Starting from the widely used realistic Bonn potentials rooted in a relativistic framework, we derive EOSs by performing the state-of-the-art relativistic Brueckner-Hartree-Fock (RBHF) calculations in the full Dirac space. The self-consistent and simultaneous consideration of both positive- and negative-energy states (NESs) of the Dirac equation allows us to avoid the uncertainties present in calculations where NESs are treated using approximations. To manifest the impact of rotational dynamics, several structural properties of neutron stars across a wide range of rotation frequencies and up to the Keplerian limit are obtained, including the gravitational and baryonic masses, the polar and equatorial radii, and the moments of inertia. Our theoretical predictions align well with the latest astrophysical constraints from the observations on massive neutron stars and joint mass-radius measurements. The maximum mass for rotating configurations can reach up to $2.93M_{\odot}$ for Bonn A potential, while the radius of a $1.4M_\odot$ neutron star for non-rotating case can be extended to around 17 km through the constant baryonic mass sequences. Relations with good universalities between the Keplerian frequency and static mass as well as radius are obtained, from which the radius of the black widow PSR J0952-0607 is predicted to be less than 19.58 km. Furthermore, to understand how rotation deforms the equilibrium shape of a neutron star, the eccentricity is also calculated. The approximate universality between the eccentricity at the Keplerian frequency and the gravitational mass is found.