New temperature dependent hyperonic equation of state: Application to rotating neutron star models and I−Q relations

Abstract

In this work we present a newly constructed equation of state (EoS), applicable to stellar core collapse and neutron star mergers including the entire baryon octet. Our EoS is compatible with the main constraints from nuclear physics and, in particular, with a maximum mass for cold β-equilibrated neutron stars of 2M in agreement with recent observations. As an application of our new EoS, we compute numerical stationary models for rapidly (rigidly) rotating hot neutron stars. We consider maximum masses of hot stars, such as protoneutron stars or hypermassive neutron stars in the postmerger phase of binary neutron star coalescence. The universality of I -Q relations at nonzero temperature for fast rotating models, comparing a purely nuclear EoS with its counterparts containing hyperons or the entire baryon octet, respectively, is discussed, too. We find that the I -Q universality is broken in our models when thermal effects become important, independent on the presence of entropy gradients. Thus, the use of I -Q relations for the analysis of protoneutron stars or merger remnant data, including gravitational wave signals from the last stages of binary neutron star mergers, should be regarded with care.

Isovector Effects in Neutron Stars, Radii, and the GW170817 Constraint

“…1. describe the NS core is matched to the low-density EOS that accounts for the NS crust. In order to describe the crust we have used the EoS developed by Hempel et al (Hempel et al (2012); Hempel and Schaffner-Bielich (2010)), which was also recently used by Marques et al (Marques et al (2017)) to augment their EoS of a NS core based on the relativistic mean field model with the density dependent interaction DD2Y, including the full baryon octet. This choice is similar to that of the QMC model and we regard it as sufficiently realistic for the purpose of this work.…”

Hyperons in hot dense matter: what do the constraints tell us for equation of state?

“…However, additional degrees of freedom in the EoS lower the maximum neutron star mass, and it was only recently that the first EoS model (DD2Y) was proposed (Marques et al 2017) containing the whole baryonic octet and being able to describe a cold neutron star with a mass of 2 M in agreement with observations (Demorest et al 2010;Fonseca et al 2016;Antoniadis et al 2013). The underlying nuclear model (DD2, Typel et al 2010) satisfies the presently accepted constraints on nuclear matter at saturation density and below obtained from nuclear experiments and theoretical calculations.…”

“…Most available general purpose EoS models including the entire baryon octet and covering at the same time a sufficiently large range in baryon number density, n B , temperature T, and hadronic charge fraction, Y Q = n Q /n B = Y e b in order to be applicable in CCSN or binary mergers are either not compatible with constraints from nuclear physics and/or a neutron star maximum mass of 2 M ; see the discussion in Oertel et al (2017). We will compare here two different EoSs, considering both all hyperons and being well compatible with the main present constraints: the DD2Y EoS (Marques et al 2017) and a new EoS based on the nuclear SFHo EoS (Steiner et al 2013), see below for details.…”

Neutron star matter with Δ isobars in a relativistic quark model

“…It is expected that high density nuclear matter may consist not only of nucleons and leptons but also several exotic components such as hyperons, mesons as well as quark matter in different forms and phases. While many studies have been conducted to address the appearance of hyperons and on the so called hyperon puzzle [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18], little work has been done to study the appearance of ∆ (1232) isobars in neutron stars. An earlier work [1] indicated the appearance of ∆ at much higher densities than the typical densities of the core of neutron stars and hence was considered of little significance to astrophysical studies.…”