Reconciliation of neutron-star masses and binding of the Λ in hypernuclei

Abstract

By relating scalar and vector couplings of the hyperons to the inferred empirical binding of the Λ hyperon in saturated nuclear matter, we obtain compatibility of this binding energy with neutron-star masses. Use of the observational constraint on the lower bound on the maximum neutron-star mass and the upper bound of the couplings that are compatible with hypernuclear levels, places bounds on the reduction in neutron-star mass that hyperons produce. For the best current estimate of nuclear-matter properties, the reduction in mass due to conversion of nucleons to hyperons is (0.71±0.15)${\mathit{M}}_{\mathrm{\odot }}$. Neutrons comprise a slight majority population ∼${\mathit{M}}_{\mathrm{\odot }}$ neutron stars with mass ∼1.5${\mathit{M}}_{\mathrm{\odot }}$.