We explore in a parameterized manner a very large range of physically plausible equations of state (EOSs) for compact stars for matter that is either purely hadronic or that exhibits a phase transition. In particular, we produce two classes of EOSs with and without phase transitions, each containing one million EOSs. We then impose constraints on the maximum mass ($M<2.16M_{\odot }$) and on the dimensionless tidal deformability ($\tilde{\mathrm{\Lambda }}<800$) deduced from GW170817, together with recent suggestions of lower limits on $\tilde{\mathrm{\Lambda }}$. Exploiting more than $10^9$ equilibrium models for each class of EOSs, we produce distribution functions of all the stellar properties and determine, among other quantities, the radius that is statistically most probable for any value of the stellar mass. In this way, we deduce that the radius of a purely hadronic neutron star with a representative mass of $1.4M_{\odot }$ is constrained to be $12.00<R_{1.4}/\mathrm{km}<13.45$ at a $2\sigma$ confidence level, with a most likely value of ${\overline{R}}_{1.4}=12.39\mathrm{km}$; similarly, the smallest dimensionless tidal deformability is ${\tilde{\mathrm{\Lambda }}}_{1.4}>375$, again at a $2\sigma$ level. On the other hand, because EOSs with a phase transition allow for very compact stars on the so-called “twin-star” branch, small radii are possible with such EOSs although not probable, i.e., $8.53<R_{1.4}/\mathrm{km}<13.74$ and ${\overline{R}}_{1.4}=13.06\mathrm{km}$ at a $2\sigma$ level, with ${\tilde{\mathrm{\Lambda }}}_{1.4}>35.5$ at a $3\sigma$ level. Finally, since these EOSs exhibit upper limits on $\tilde{\mathrm{\Lambda }}$, the detection of a binary with a total mass of $3.4M_{\odot }$ and ${\tilde{\mathrm{\Lambda }}}_{1.7}>461$ can rule out twin-star solutions.

We study the equation of state of hyperon-rich matter in neutron stars using an extended relativistic mean-field model. We take special care of the recently proposed nonlinear behavior of the vector field providing a much better agreement with Dirac-Brückner calculations. The hyperon-hyperon interaction is also implemented by introducing additional meson exchanges. With these new terms we avoid the instability found at high densities while keeping the excellent description for finite nuclear systems. We also demonstrate within the mean-field approach that the presence of hyperons inside neutron stars on one hand and the hyperon-hyperon interactions on the other hand make the onset of kaon condensation less favorable. © 1996 The American Physical Society.

With the discovery of massive neutron stars such as PSR J1614-2230, the question has arisen of whether exotic matter such as hyperons can exist in the neutron star core. We examine the conditions under which hyperons can exist in massive neutron stars. We consistently investigate the vector baryon-meson coupling, going from the SU(6) quark model to a broader SU(3) symmetry. We propose that the maximum neutron star mass decreases linearly with the strangeness content fs of the neutron star core as Mmax(fs)=Mmax(0)$-${}0.6M$\bigodot${}(fs/0.1), which seems to be independent of the underlying nuclear equation of state and the vector baryon-meson coupling scheme. Thus, pulsar mass measurements can be used to constrain the hyperon fraction in neutron stars.