Neutron stars with hyperon cores: stellar radii and EOS near nuclear density

Abstract

The existence of 2 Msun pulsars puts very strong constraints on the equation of state (EOS) of neutron stars (NSs) with hyperon cores, which can be satisfied only by special models of hadronic matter. The radius-mass relation for these models is sufficiently specific that it could be subjected to an observational test with future X-ray observatories. We want to study the impact of the presence of hyperon cores on the radius-mass relation for NS. We aim to find out how, and for which particular stellar mass range, a specific relation R(M), where M is the gravitational mass, and R is the circumferential radius, is associated with the presence of a hyperon core. We consider a set of 14 theoretical EOS of dense matter, based on the relativistic mean-field (RMF) approximation, allowing for the presence of hyperons in NSs. We seek correlations between R(M) and the stiffness of the EOS below the hyperon threshold needed to pass the 2 Msun test. For NS masses 1.0<M/Msun<1.6, we get R>13km, because of a very stiff pre-hyperon segment of the EOS. At nuclear density, the pressure is significantly higher than a robust upper bound obtained recently using chiral effective field theory. If massive NSs do have a sizable hyperon core, then according to current models the radii for M=1.0-1.6 Msun are necessarily >13km. If, on the contrary, a NS with a radius R<12 km is observed in this mass domain, then sizable hyperon cores in NSs, as we model them now, are ruled out. Future X-ray missions with <5% precision for a simultaneous M and R measurement will have the potential to solve the problem with observations of NSs. Irrespective of this observational test, present EOS allowing for hyperons that fulfill condition M_max>2 Msun yield a pressure at nuclear density that is too high relative to up-to-date microscopic calculations of this quantity.

10 pages, 10 figures, published in A&A

References in corpus (11)

• Shapiro delay measurement of a two solar mass neutron star
• A Massive Pulsar in a Compact Relativistic Binary
• New Hyperon Equations of State for Supernovae and Neutron Stars in Density-dependent Hadron Field Theory
• Proto-Neutron and Neutron Stars in a Chiral SU(3) Model
• Hypernuclear Physics for Neutron Stars
• Hyperon mixing and universal many-body repulsion in neutron stars
• Improved Mass and Radius Constraints for Quiescent Neutron Stars in Omega Cen and NGC 6397
• Equation of state and thickness of the inner crust of neutron stars
• Rejecting proposed dense-matter equations of state with quiescent low-mass X-ray binaries
• The effect of accretion on the measurement of neutron star mass and radius in the low-mass X-ray binary 4U 1608-52
• The mass and the radius of the neutron star in the transient low mass X-ray binary SAX J1748.9-2021

Cited by in corpus (21)

• Wormholes in $R^2$-gravity within the $f(R,T)$ formalism
• Equation of State for Nucleonic and Hyperonic Neutron Stars with Mass and Radius Constraints
• Extreme Matter meets Extreme Gravity: Ultra-heavy neutron stars with crossovers and first-order phase transitions
• Higher-order symmetry energy and neutron star core-crust transition with Gogny forces
• Improved Treatment of Dark Matter Capture in Neutron Stars III: Nucleon and Exotic Targets
• Consequences of a strong phase transition in the dense matter equation of state for the rotational evolution of neutron stars
• Bayesian inference of signatures of hyperons inside neutron stars
• Hyperon star in a modified quark meson coupling model
• Examination of strangeness instabilities and effects of strange meson couplings in dense strange hadronic matter and compact stars
• The axion-baryon coupling in SU(3) heavy baryon chiral perturbation theory
• Tidal heating as a direct probe of strangeness inside neutron stars
• Fast cooling and internal heating in hyperon stars
• Influence of pressure anisotropy and non-metricity parameter on mass-radius relation and stability of millisecond pulsar in $f(Q)$ gravity
• Correlation of the hyperon potential stiffness with hyperon constituents in neutron stars and heavy-ion collisions
• Thermal luminosity degeneracy of magnetized neutron stars with and without hyperon cores
• Equation of state in neutron stars and supernovae
• Detecting Hyperons in neutron stars -- a machine learning approach
• Neutron star equation of state: identifying hadronic matter characteristics
• Investigating Evolving Wormholes in $f(R,T)$ Gravity
• Learning about neutron star composition from the slope of the mass-radius diagram
• On the Destabilization of High-Mass Neutron Stars by the Emergence of $d^{\ast }$-Hexaquarks