The existence of neutron stars with 2M requires strong stiffness of the equation of state (EoS) of neutron-star matter. We introduce a multi-Pomeron exchange potential (MPP) working universally among three- and four-baryon systems 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) theory 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 are obtained on the basis of terrestrial data. Neutron-star radii R at a typical mass 1.5M are predicted to be 12.3-13.1 km. The uncertainty of calculated radii is mainly from the ratio of three- and four-Pomeron coupling constants, which cannot be fixed by any terrestrial experiment. Though values of R(1.5M) 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∼2M. If R(1.5M) is less than about 12.3 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 ±5%.
ASJC Scopus subject areas
- Nuclear and High Energy Physics