Maximum Mass Of Quark Stars Research Articles

Constraints of the maximum mass of quark stars based on postmerger evolutions

Constraints of the maximum mass of quark stars based on postmerger evolutions

Interacting quark star with pressure anisotropy and recent astrophysical observations

This paper investigates the internal structure and equation of state (EoS) of quark stars (QS) with pressure anisotropy, incorporating recent astrophysical observations. Utilizing perturbative QCD corrections and color superconductivity, the EoS is expressed as a dimensionless function dependent on a single parameter, providing a comprehensive exploration of strong interaction effects. By rescaling the EoS and introducing dimensionless variables, the study encompasses scenarios ranging from noninteracting quark matter to extreme stiffness characterized by a parameter, λ̄. Anisotropic QS configurations are constructed using a spherically symmetric metric, with locally anisotropic matter described by a generalized EoS for tangential pressure. The Tolman–Oppenheimer–Volkoff equations governing star structure are presented in dimensionless form, and numerical solutions explore the parameter space defined by effective bag constants and λ̄. Mass–radius relations and the compactness of anisotropic QSs are analyzed under various model parameter variations, considering constraints from pulsar masses and gravitational wave phenomena. The study highlights the influence of pressure anisotropy on the maximum mass of QSs and discusses the impact of model parameters on internal properties. Additionally, the paper considers static stability, adiabatic index, and sound velocity profiles, providing a comprehensive understanding of QS behavior. Overall, this investigation contributes valuable insights into the properties of QSs and their compatibility with observational constraints, offering a detailed exploration of their EoS and internal structure.

Constraints on the maximum mass of quark star and the GW 190814 event

Gravitational-waves (GWs) data have widely been used for testing preferred modified gravity theories. In this paper, we investigate the possibility of testing them in the strong gravity regime by looking at the properties of compact objects in dense matter physics. In this direction modified gravity theories such as f(R, T) gravity can be tested with the recently discovered compact binary merger, GW 190814, containing a compact object with mass 2.50–2.67 M_{odot }. By considering these constraints on maximum mass of such an object, we predict the existence of quark stars (QSs) made of quark matter in the color-flavor-locked (CFL) phase of color superconductivity. Such a state is significantly more bound than ordinary quark matter and enhances the possibility of the existence of a pure stable QS. We focus on the following aspects in particular: mass–radius profile, mass-central mass density relation, compactness and the corresponding effective adiabatic index for stability related issues. Our result implies that predicted properties for QSs are well consistent with GW 190814 observational data that helps us to impose constraints on the theoretical models of dense nuclear matter.

Quark matter and quark stars in a quasiparticle model

We investigate the properties of the equation of state of strange-quark matter and $u\text{\ensuremath{-}}d$ quark matter, the sound velocity of quark matter, the stability region for star matter, the maximum mass of quark stars (QSs), and the tidal deformability for QSs by using a quark quasiparticle model. Our results indicate that the recently discovered heavy compact stars PSR $\mathrm{J}0348+\text{ }0432$, MSR $\mathrm{J}0740+6620$, and PSR $\mathrm{J}2215+5135$, and especially the GW190814s secondary component ${m}_{2}$ can be well described as QSs within the quasiparticle model.

Deformation of a magnetized quark star in Rastall gravity

We have investigated the influence of strong magnetic fields at the center of the quark stars which is an impact to shape of stars by using Einstein’s theory of gravity, which uses the EoS CIDDM model. Our focus in this study is to compare the results of the deformation degree of quark stars from theory of gravity Einstein and Rastall, where on Rastall gravity introduced degree of freedom λ, where we use variations of λ = 1, 2, 3, 4 and 5, where Rastall gravity will reduced to Einstein theory of gravity at the value of λ = 1. We obtained for each EoS with different values of κ1 indicate the degree of deformation tends toward prolate at the maximum mass of the same quark star for the both theories, the most significant difference on Rastall gravity is the maximum mass of quark stars increases with the high value of the λ we set.

Quark matter and quark stars in strong magnetic fields at finite temperature within the confined-isospin-density-dependent mass model

We study the properties of strange quark matter (SQM) and quark stars (QSs) in strong magnetic fields within the extended confined isospin-density-dependent mass (CIDDM) model including the temperature dependence of the equivalent mass for quarks. The quark symmetry energy, quark symmetry free energy, and the equation of state (EOS) of SQM in constant magnetic fields at finite temperature are investigated, and it is found that including the temperature dependence in CIDDM model and considering strong magnetic fields can both significantly influence the properties of the SQM and the maximum mass of quark stars. Using the density-dependent magnetic field and assuming two extreme cases for the magnetic field orientation in QSs (the radial orientation in which the local magnetic fields are along the radial direction and the transverse orientation in which the local magnetic fields are randomly oriented but perpendicular to the radial orientation), we analyze the mass-radius relations for different stages of the protoquark stars (PQSs) along the star evolution. Our results indicate that the maximum mass of magnetized PQSs may depend on not only the strength distribution and the orientation of the magnetic fields inside the PQSs, but also the heating process and the cooling process in the star evolution.

Warm asymmetric quark matter and protoquark stars within the confined isospin-density-dependent mass model

We extend the confined-isospin-density-dependent mass (CIDDM) model to include temperature dependence of the equivalent mass for quarks. Within the CIDDM model, we study the equation of state (EOS) for $\beta$-equilibrium quark matter, quark symmetry energy, quark symmetry free energy, and the properties of quark stars at finite temperature. We find that including the temperature dependence of the equivalent mass can significantly influence the properties of the strange quark matter (SQM) as well as the quark symmetry energy, the quark symmetry free energy, and the maximum mass of quark stars at finite temperature. The mass-radius relations for different stages of the proto-quark stars (PQSs) along the star evolution are analyzed. Our results indicate that the heating (cooling) process for PQSs will increase (decrease) the maximum mass within CIDDM model by including temperature dependence of the equivalent mass for quarks.

Quark magnetar in three-flavor Nambu–Jona-Lasinio model under strong magnetic fields with two types of vector interactions

We investigate the properties of strange quark matter (SQM) and quark stars (QSs) in the framework of SU(3) Nambu--Jona-Lasinio (NJL) model with two types of vector interactions under strong magnetic fields: (1) the flavor-dependent repulsion among $u$, $d$, and $s$ quarks with the coupling constant ${G}_{V}$, and (2) the universal repulsion and the vector-isovector interaction with the coupling constants ${g}_{V}$ and ${G}_{IV}$. The effects of the two types of vector interactions on the constituent quark mass, vacuum quark mass, quark chemical potential, and quark fraction in SQM under strong magnetic fields are studied, and the results indicate that these physical quantities for SQM are all sensitive to the two types of vector interactions in NJL model under magnetic fields. Using a density-dependent magnetic field profile which is introduced to describe the magnetic field strength distribution inside the magnetars, we calculate the properties of spherical QSs by using two extreme cases for the orientation of the magnetic field inside the stars, i.e., the radial orientation in which the magnetic fields are along the radial direction in stars, and the transverse orientation in which the magnetic fields are randomly oriented in the plane which is perpendicular to the radial direction. Our results indicate that the maximum mass of QSs may dependent on both the strength distribution and the orientation of the magnetic fields inside QSs by using SU(3) NJL model.

Quark stars in strong magnetic fields

Within the confined isospin- and density-dependent mass model, we study the properties of strange quark matter (SQM) and quark stars (QSs) in strong magnetic fields. The equation of state of SQM under a constant magnetic field is obtained self-consistently and the pressure perpendicular to the magnetic field is shown to be larger than that parallel to the magnetic field, implying that the properties of magnetized QSs generally depend on both the strength and the orientation of the magnetic fields distributed inside the stars. Using a density-dependent magnetic field profile which is introduced to mimic the magnetic field strength distribution in a star, we study the properties of static spherical QSs by assuming two extreme cases for the magnetic field orientation in the stars, i.e., the radial orientation in which the local magnetic fields are along the radial direction, and the transverse orientation in which the local magnetic fields are randomly oriented but perpendicular to the radial direction. Our results indicate that including the magnetic fields with radial (transverse) orientation can significantly decrease (increase) the maximum mass of QSs, demonstrating the importance of the magnetic field orientation inside the magnetized compact stars.

Two-flavor quark matter in the perturbation theory with full thermodynamic consistency

Direct extrapolation of the strong interaction between quarks in pure perturbative calculation has a problem of thermodynamic inconsistency. A new term determined by thermodynamic consistency requirement could resolve it. This new term plays an important role at lower density in describing the equation of state of quark matter, while it is negligible at high density. Accordingly, the density behavior of the sound velocity becomes more reasonable, and the maximum mass of quark stars can be as large as two times the solar mass.

A family of exact solutions of Einstein-Maxwell field equations in isotropic coordinates: an application to optimization of quark star mass

In the present paper, we have obtained a class of charged super dense star models, starting with a static spherically symmetric metric in isotropic coordinates for perfect fluid by considering Hajj-Boutros (in J. Math. Phys. 27:1363, 1986) type metric potential and a specific choice of electrical intensity which involves a parameter K. The resulting solutions represent charged fluid spheres joining smoothly with the Reissner-Nordstrom metric at the pressure free interface. The solutions so obtained are utilized to construct the models for super-dense star like neutron stars (ρ b =2 and 2.7×1014 g/cm3) and Quark stars (ρ b =4.6888×1014 g/cm3). Our solution is well behaved for all values of n satisfying the inequalities $4 < n \le4(4 + \sqrt{2} )$ and K satisfying the inequalities 0≤K≤0.24988, depending upon the value of n. Corresponding to n=4.001 and K=0.24988, we observe that the maximum mass of quark star M=2.335M ⊙ and radius R=10.04 km. Further, this maximum mass limit of quark star is in the order of maximum mass of stable Strange Quark Star established by Dong et al. (in arXiv:1207.0429v3 , 2013). The robustness of our results is that the models are alike with the recent discoveries.

Quark stars with the density-dependent quark mass model

The recent observation of the pulsar PSR J1614-2230 with a mass of 1.97±0.04M⊙ gives a strong constraint on the equation of state (EoS) of the dense matter in compact stars. In this work, we calculate the maximum mass of quark stars with the density-dependent quark mass model, and explore the parameter ranges for this model fully, by considering the constraints of absolute stability of strange quark matter and the mass of PSR J1614-2230. Without the color-superconductivity, the maximum mass of unpaired quark stars is more sensitive to the parameter C, and complies with the constraints within the range of 96MeVfm-3≲C≲130MeVfm-3. The largest mass can reach 2.25M⊙ at C≃96.54MeVfm-3 and ms0≃145MeV. For the quark stars composed of the quark matter in color-flavor locked (CFL) phase, we can obtain quite large maximum masses at a sufficiently high gap value, but the value of ms0 is very important in deciding the maximum mass of the CFL quark stars.