Neutron-star radii based on realistic nuclear interactions

TL;DR

This paper models neutron-star radii using realistic nuclear interactions and a multi-pomeron exchange potential to stiffen the EoS, predicting radii around 12.3 to 13.0 km for 1.5 solar mass stars, with implications for hyperon effects.

Contribution

Introduces a multi-pomeron exchange potential to stiffen the EoS and predicts neutron-star radii based on terrestrial nuclear data and advanced many-body methods.

Findings

Neutron-star radii at 1.5 M_sun are predicted to be 12.3-13.0 km.

Maximum neutron star mass exceeds 2 M_sun with the proposed EoS.

Uncertainty in radii mainly from hyperon-mixing effects.

Abstract

The existence of neutron stars with $2M_\odot$ requires the strong stiffness of the equation of state (EoS) of neutron-star matter. We introduce a multi-pomeron exchange potential (MPP) working universally among 3- and 4-baryons to stiffen the EoS. Its strength is restricted by analyzing the nucleus-nucleus scattering with the G-matrix folding model. The EoSs are derived using the Brueckner-Hartree-Fock (BHF) and the cluster variational method (CVM) with the nuclear interactions ESC and AV18. The mass-radius relations are derived by solving the Tolmann-Oppenheimer-Volkoff (TOV) equation, where the maximum masses over $2M_\odot$ are obtained on the basis of the terrestrial data. Neutron-star radii $R$ at a typical mass $1.5M_\odot$ are predicted to be $12.3\!\sim\!13.0$ km. The uncertainty of calculated radii is mainly from the ratio of 3- and 4-pomeron coupling constants, which cannot be fixed by any terrestrial experiment. Though values of $R(1.5M_\odot)$ are not influenced by hyperon-mixing effects, finely-observed values for them indicate degrees of EoS softening by hyperon mixing in the region of $M\!\sim\!2M_\odot$. If $R(1.5M_\odot)$ is less than about 12.4 km, the softening of EoS by hyperon mixing has to be weak. Useful information can be expected by the space mission NICER offering precise measurements for neutron-star radii within $\pm 5\%$.