Abstract
Abstract The structured hadron-quark mixed phase, known as the pasta phase, is expected to appear in the core of massive neutron stars. Motivated by the recent advances in astrophysical observations, we explore the possibility of the appearance of quarks inside neutron stars and check its compatibility with current constraints. We investigate the properties of the hadron-quark pasta phases and their influences on the equation of state (EOS) for neutron stars. In this work, we extend the energy minimization (EM) method to describe the hadron-quark pasta phase, where the surface and Coulomb contributions are included in the minimization procedure. By allowing different electron densities in the hadronic and quark matter phases, the total electron chemical potential with the electric potential remains constant, and local β equilibrium is achieved inside the Wigner–Seitz cell. The mixed phase described in the EM method shows the features lying between the Gibbs and Maxwell constructions, which is helpful for understanding the transition from the Gibbs construction to the Maxwell construction with increasing surface tension. We employ the relativistic mean-field model to describe the hadronic matter, while the quark matter is described by the MIT bag model with vector interactions. It is found that the vector interactions among quarks can significantly stiffen the EOS at high densities and help enhance the maximum mass of neutron stars. Other parameters like the bag constant can also affect the deconfinement phase transition in neutron stars. Our results show that hadron-quark pasta phases may appear in the core of massive neutron stars that can be compatible with current observational constraints.
Highlights
The appearance of deconfined quark matter, which is expected to appear in the core of massive neutron stars, has received increasing attention recently because of its relevance to astrophysical observations (Lattimer & Prakash 2016; Baym et al 2018; Annala et al 2020)
Motivated by the recent advances in astrophysical observations, we studied the properties of the hadronquark pasta phases, which may appear in the interior of massive neutron stars
The structured mixed phase is described within the Wigner–Seitz approximation, where the whole space is divided into equivalent cells with a geometric symmetry
Summary
The appearance of deconfined quark matter, which is expected to appear in the core of massive neutron stars, has received increasing attention recently because of its relevance to astrophysical observations (Lattimer & Prakash 2016; Baym et al 2018; Annala et al 2020). Several studies have suggested that the secondary in GW190814 may be a rapidly rotating neutron star (Li et al 2020; Most et al 2020; Tsokaros et al 2020; Zhang & Li 2020) It could be considered as a heavy neutron star containing deconfined quark matter, where the inclusion of quarks has significant impact on the observations (Tan et al 2020; Demircik et al 2021; Dexheimer et al 2021). In light of these recent developments in astronomy, it would be interesting and informative to explore possible structures of the hadronquark mixed phase in massive neutron stars
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