Unified equation of state for neutron stars on a microscopic basis

Abstract

We derive a new equation of state (EoS) for neutron stars (NS) from the outer crust to the core based on modern microscopic calculations using the Argonne v 18 potential plus three-body forces computed with the Urbana model. To deal with the inhomogeneous structures of matter in the NS crust, we use a recent nuclear energy density functional that is directly based on the same microscopic calculations, and which is able to reproduce the ground-state properties of nuclei along the periodic table. The EoS of the outer crust requires the masses of neutron-rich nuclei, which are obtained through Hartree-Fock-Bogoliubov calculations with the new functional when they are unknown experimentally. To compute the inner crust, Thomas-Fermi calculations in Wigner-Seitz cells are performed with the same functional. Existence of nuclear pasta is predicted in a range of average baryon densities between 0.067 fm −3 and 0.0825 fm −3 , where the transition to the core takes place. The NS core is computed from the new nuclear EoS assuming non-exotic constituents (core of npeμ matter). In each region of the star, we discuss the comparison of the new EoS with previous EoSs for the complete NS structure, widely used in astrophysical calculations. The new microscopically derived EoS fulfills at the same time a NS maximum mass of 2 M with a radius of 10 km, and a 1.5 M NS with a radius of 11.6 km.

A new statistical method for the structure of the inner crust of neutron stars

“…In the low density region, we observe a very well pronounced minimum at Z=38. This value is compatible with the typical drip-line nuclei found in the outer crust [85][86][87]. At ρ b = 0.0006 fm −3 , we observe a transition from Z=38 to Z=50.…”

“…In Ref. [85], where shell effects are not included, this feature is not present and the proton clusters are typically smaller Z ∈ [24−36].…”

Neutron star properties and the equation of state for the core

“…Consequently, calculating the crust equation of state (EOS) is much less straightforward than for the core, which explains the smaller number of crust EOS available compared to those for the core. In particular, few unified EOS, i.e., those based on the same nuclear model for the crust and core, have been developed; see, for example, Douchin & Haensel (2001), Fantina et al (2013), Pearson et al (2014), Sharma et al (2015), Fortin et al (2016). Therefore non-unified EOS are often used, assuming different nuclear interaction models for the crust and core.…”

The attribute of rotational profile to the hyperon puzzle in the prediction of heaviest compact star

“…[40][41][42][43][44][45] It is well known that the theoretical Mass-Radius relation depends on the rotation frequency and also the presence of an exotic core in massive neutron star. Within the present scenario, all neutron stars rotate and there are many millisecond pulsars with rotation frequency ≥ 500 Hz (10 accreting X-ray pulsars and 14 radio/gamma-ray pulsars).…”

“…[76][77][78][79] In addition to that, the generalized model having the low lying octet of baryons makes it difficult to obtain a neutron star mass greater than 2.0M . 43,44,77,79 In continuation of our earlier work, 79 we here analyze the rotational attributes of neutron star with various hyperon-meson couplings within the framework of effective field theory motivated relativistic mean field model (E-RMF). 43,76,79,80 The degrees of freedom in this theory are nucleons interacting through the exchange of iso-scalar scalar σ−, iso-scalar vector ω−, and iso-vector-vector ρ− meson fields.…”