Neutron Stars: A Novel Equation of State with Induced Surface Tension

Abstract

A novel equation of state with the surface tension induced by particles' interactions was generalized to describe the properties of the neutron stars (NSs). In this equation the interaction between particles occurs via the hard core repulsion by taking into account the proper volumes of particles. Recently, this model was successfully applied to the description of the properties of nuclear and hadron matter created in collisions of nucleons. The new approach is free of causality problems and is fully thermodynamically consistent, which enables us to use it for the investigation of the strongly interacting matter phase-diagram properties in a wide range of temperatures and baryon densities, including NSs. Here, we have calculated the mass-radius relations for a compact star using the Tolmann-Oppenheimer-Volkov (TOV) equation for two sets of parameters that satisfy the existing constraints. Accordingly, we found parameter values that are in good agreement with the same ones obtained from the nuclear-nuclear collision data analysis. The astrophysical constraints suggest that the hard core radius of baryons can vary between 0.425 fm and 0.476 fm.

Equation of State of Quantum Gases Beyond the Van der Waals Approximation

“…This conclusion is well supported by the recent simulations of the neutron star properties with masses more than two Solar ones [40] which also favor the nucleon hard-core radii below than 0.52 fm. Furthermore, the small values of the hard-core radii provide the fulfillment of the causality condition in hadronic phase [24,25,40,45], while a possible break of causality occurs in the region where the hadronic degrees of freedom are not relevant [45]. Hence, in contrast to Ref.…”

“…Expressing Σ from Eq. (41) and substituting it into (40), one finds the densities of particle number (˜2( , 2 ) ≡ 2 (1 − 0 1 ))…”

The Induced Surface Tension Contribution for the Equation of State of Neutron Stars

“…Our analysis demonstrates that a realistic dependence of the total NS mass on its radius is obtained for α from 1.2 to 1.3. At the same time, the α = 1.1 also reported in Sagun & Lopes (2017) is not consistent with a realistic mass-radius diagram. This allows us to conclude that the contribution coming from the nuclear asymmetry energy with realistic values of J and L narrows a range of possible values of α.…”

“…This comparative study of two sets of IST EoS allows us to draw some generic conclusions: the nucleon hard core ra- dius defines the stiffness of the EoS as first shown by Sagun & Lopes (2017), the parameter α defines the upper part of the mass-radius relation curve, the reduction of B sym shifts the radius of the NSs to higher values, and the attraction term, which is accounted for via the mean field potential U(n id B ), defines the part of the NS mass-radius relation that corresponds to the low masses and high radii.…”

Neutron stars meet constraints from high and low energy nuclear physics

“…In our approach we account for the long range attraction of the mean field type as well as for the strong short range repulsion between particles. The latter is modelled by the hard core repulsion within the framework of induced surface tension (IST) which was successfully applied for modelling properties of symmetric nuclear matter [4], analysis of hadron yields measured in HIC from AGS [5] to ALICE [6] energies and to description of compact astrophysical objects [7]. This approach allows us to go beyond the usual Van der Waals approximation and to safely describe baryonic matter at high densities.…”