Hybrid star phenomenology from the properties of the special point

TL;DR

This paper investigates hybrid stars with color superconducting quark cores, analyzing phase transition characteristics, fitting quark matter EoS models, and constraining model parameters to explain observed massive pulsars.

Contribution

It introduces an empirical relation linking mass-radius special points to quark matter model parameters, aiding in constraining hybrid star models.

Findings

The quark matter EoS can be fitted by the Alford-Braby-Paris-Reddy model.

Special points in mass-radius diagrams are characterized and related to model parameters.

Hybrid star models can explain the mass of PSR J0952-0607 as a quark core star.

Abstract

We study the properties of hybrid stars containing a color superconducting quark matter phase in their cores, which is described by the chirally symmetric formulation of the confining relativistic density functional approach. It is shown that depending on the dimensionless vector and diquark couplings of quark matter, the characteristics of the deconfinement phase transition are varied, allowing us to study the relation between those characteristics and mass-radius relations of hybrid stars. Moreover, we show that the quark matter equation of state (EoS) can be nicely fitted by the Alford-Braby-Paris-Reddy model that gives a simple functional dependence between the most important parameters of the EoS and microscopic parameters of the initial Lagrangian. Based on it, we analyze the special points of the mass-radius diagram in which several mass-radius curves intersect. Using the found empirical relation between the mass of the special point, the maximum mass of the mass-radius curve, and the onset mass of quark deconfinement, we constrain the range of values of the vector and diquark couplings of the quark matter model. With this constraint, we construct a family of mass-radius curves, which allow us to describe the black widow pulsar PSR J0952-0607 with a mass of $2.35\pm 0.17~\rm M_\odot$ as a hybrid star with a color superconducting quark matter core.