Structure Of Quark Star Research Articles

Color-flavor locked quark stars in Rastall–Rainbow gravity

We investigate the hydrostatic equilibrium configurations of strange stars within the framework of Rastall–Rainbow theory of gravity. These stars are primarily composed of strange quark matter, with its distribution governed by the color-flavor-locked phase of quark matter equation of state (EoS). Using this EoS, we numerically solve the modified Tolman–Oppenheimer–Volkoff equation to obtain different quark star models. We find that the parameters from this modified gravity have specific contributions to the structure of quark stars and introduce new descriptions for massive celestial bodies. Also, the mass–radius relation strongly depends on the parameters from the considered EoS. Furthermore, we analyze the impact of these parameters on the gravitational redshift and compactness of quark stars.

Effects of anisotropic pressure on interacting quark star structure

Perturbative Quantum Chromodynamics (pQCD) corrections and color superconductivity predict that strongly interacting matter can reveal new physical phenomena under extreme conditions. Taking into account these interaction effects, we investigate the role of anisotropic pressure in quark stars composed of interacting quark matter. Adopting two physically well-motivated anisotropy profiles, we numerically solve the stellar structure equations in order to explore the consequences of anisotropic pressure on various macroscopic properties such as radius, gravitational mass, surface redshift, moment of inertia, tidal Love number and oscillation spectrum. Remarkably, for both anisotropy models, negative anisotropies increase the radial stability of interacting quark stars, while the opposite occurs for positive anisotropies. However, for the Bowers-Liang profile, the central density corresponding to the maximum-mass point does not coincide with the central density where the squared oscillation frequency vanishes, indicating that the existence of stable anisotropic interacting quark stars is possible beyond the maximum mass for negative anisotropies. Additionally, we compare our theoretical predictions with several observational mass-radius measurements and tidal deformability constraints, which suggest that both strong interaction effects and anisotropy effects play a crucial role in describing compact stars observed in the Universe.

Anisotropic quark stars in de Rham–Gabadadze–Tolley like massive gravity

We investigate the structure of quark stars in de Rham–Gabadadze–Tolley like massive gravity with an anisotropic matter source. The MIT bag model as the equation of state for compact stars is used to numerically solve the modified Tolman–Oppenheimer–Volkoff equation. We analyze the effects of bag constant, anisotropy parameter and massive gravity parameters on the structure of quark stars. The results show that the mass and radius of the quark star depend on these parameters significantly, and the maximum mass can satisfy the observational data for the massive pulsar PSR J0348+0432. Furthermore, we also discuss other properties of quark stars, including dynamical stability, Schwarzschild radius and compactness.

The mass–radius relation for quark stars in energy–momentum squared gravity

We study the structure of quark stars (QSs) adopting homogeneously confined matter inside the star with a 3-flavor neutral charge and a fixed strange quark mass ms. We explore the internal structure, and the physical properties of specific classes of QSs in the recently proposed energy–momentum squared gravity (EMSG). Also, we obtain the mass–radius (M–R) and mass–central energy density (M–ρc) relations for QS using the QCD motivated EoS. The maximum mass for QSs in EMSG is investigated depending on the presence and absence of the free parameter α. Furthermore, the stability of stars is determined by the condition dMdρc>0. We observe that consideration of the EMSG has specific contributions to the structure of QSs.

R2-gravity quark stars from perturbative QCD

We investigate the structure of quark stars in the framework of f(R)= R + αR 2 gravity using an equation of state for cold quark matter obtained from perturbative QCD, parametrized only by the renormalization scale. We show that a considerably large range of the free parameter α, within and even beyond the constraints previously reported in the literature, yield non-negligible modifications in the mass and radius of stars with large central mass densities. Their stability against baryon evaporation is analyzed through the behavior of the associated total binding energies which are slightly affected by the modified gravity term in the regime of high proper (baryon) masses.

Structure of Quark Star: A Comparative Analysis of Bayesian Inference and Neural Network Based Modeling

Abstract In this work, we compare two powerful parameter estimation methods, namely Bayesian inference and neural network based learning, to study the quark matter equation of state with constant speed of sound parameterization and the structure of the quark stars within the two-family scenario. We use the mass and radius estimations from several X-ray sources and also the mass and tidal deformability measurements from gravitational wave events to constrain the parameters of our model. The results found from the two methods are consistent. The predicted speed of sound is compatible with the conformal limit.

Structure of Quark Stars

AbstractThis paper gives an brief overview of the structure of hypothetical strange quarks stars (quark stars, for short), which are made of absolutely stable 3-flavor strange quark matter. Such objects can be either bare or enveloped in thin nuclear crusts, which consist of heavy ions immersed in an electron gas. In contrast to neutron stars, the structure of quark stars is determined by two (rather than one) parameters, the central star density and the density at the base of the crust. If bare, quark stars possess ultra-high electric fields on the order of 1018 to 1019 V/cm. These features render the properties of quark stars more multifaceted than those of neutron stars and may allow one to observationally distinguish quark stars from neutron stars.

The effect of dynamical quark mass on the calculation of a strange quark star's structure

We discuss the dynamical behavior of strange quark matter components, in particular the effects of density dependent quark mass on the equation of state of strange quark matter. The dynamical masses of quarks are computed within the Nambu-Jona-Lasinio model, then we perform strange quark matter calculations employing the MIT bag model with these dynamical masses. For the sake of comparing dynamical mass interaction with QCD quark-quark interaction, we consider the one-gluon-exchange term as the effective interaction between quarks for the MIT bag model. Our dynamical approach illustrates an improvement in the obtained equation of state values. We also investigate the structure of the strange quark star using Tolman-Oppenheimer-Volkoff equations for all applied models. Our results show that dynamical mass interaction leads to lower values for gravitational mass.

The Renormalized Equation of State and Quark Star

By means of the EOS of QCD at zero temperature and finite quark chemical potential we proposed [Phys. Rev. D 78(2008)054001] in the framework of rainbow-ladder approximation of Dyson-Schwinger approach, we investigate the structure of quark star and its property. It is found that the mass-radius relation in our model is very different from that of usual quark star models, but similar to neutron star models. The obtained mass of quark star is about 1.75M⊙ ∼ 2.2M⊙. The obtained radius of quark star is 22 ∼ 26 km, which is obviously larger than the results in other models. The reason for this discrepancy is analyzed.

Bag model and quark star

In this paper, incorporating the property of the vacuum negative pressure, namely, the bag constant, we presented a new model of the equation of state (EOS) of quark matter at finite chemical potential and zero temperature. By comparing our EOS with Fraga {\it et~al.}'s EOS and SQM1 model, one find that our EOS is softer than Fraga {\it et~al.}'s EOS and SQM1 model. The reason for this difference is analyzed. With these results we investigate the structure of quark star. A comparison between our model of quark star and other models is made. The obtained mass of quark star is $ 1.3 \sim 1.66 M_\odot$ and the radius is $9.5 \sim 14 Km$. One can see that our star's compactness is smaller than that of other two models.

Quark matter in compact stars

Recently reported massive compact stars ( M ∼ 2 M ⊙ ) have provided strong constraints on the properties of the ultradense matter beyond the saturation nuclear density. Therefore, realistic quark or hybrid star models must be compatible with these observational data. Some used equations of state (EoS) describing quark matter are in general too soft and hence are not suitable to explain the stability of high compact star masses. In this work, we present the calculations of static spherically symmetric quark star structure by using an equation of state which takes into account the superconducting colour-flavour locked phase of the strange quark matter. In addition, some fundamental aspects of QCD (asymptotic freedom and confinement) are considered by means of a phenomenological description of the deconfined quark phase, the density-dependent quark mass model. We discuss the influence of the obtained quark matter equation of state on the mass-radius relationship of quark stars. Massive quark stars are found due to the stiffness of the equation of state, when reasonable values of the superconducting gap, taken as a free parameter, are used.

On a possible mechanism of low surface magnetic field structure of quark stars

Following some of the recent articles on hole super-conductivity and related phenomena by Hirsch (Phys. Lett. A 134:451, 1989; Phys. Rev. B 68:184502, 2003a; Phys. Rev. B 71:184521, 2005a and Phys. Lett. A 345:453, 2005b) a simple model is proposed to explain the observed low surface magnetic field of the expected quark stars. It is argued that the diamagnetic moments of the electrons circulating in the electro-sphere induce a magnetic field, which forces the existing quark star magnetic flux density to become dilute. For the sake of completeness, we have also included the analyses of instability at the normal-super-conducting interface due to excess accumulation of magnetic flux lines. The instability at the interface has also been studied numerically.

Effects of strong interaction on the structure of color-flavor-locked quark stars

The static spherically symmetric quark star structure is calculated by using an equation of state which takes into account the superconducting color-flavor locked phase of the strange quark matter. Some fundamental aspects of QCD (asymptotic freedom and confinement) are considered by means of a phenomenological description of the deconfined quark phase, namely, the density-dependent quark mass model. The effects from the strong interaction described by these models can affect the equation of state of the quark matter substantially. In this work we discuss the influence of these effects on the conventional mass-radius relationship of quark stars. Massive quark stars are found due to the stiffness of the equation of state at low densities, when reasonable values of the superconducting gap, taken as a free parameter, are used.

QUARK MATTER IN NEUTRON STARS: AN APERÇU

The existence of deconfined quark matter in the superdense interior of neutron stars is a key question that has drawn considerable attention over the past few decades. Quark matter can comprise an arbitrary fraction of the star, from 0 for a pure neutron star to 1 for a pure quark star, depending on the equation of state of matter at high density. From an astrophysical viewpoint, these two extreme cases are generally expected to manifest different observational signatures. An intermediate fraction implies a hybrid star, where the interior consists of mixed or homogeneous phases of quark and nuclear matter, depending on surface and Coulomb energy costs, as well as other finite size and screening effects. In this review, we discuss what we can deduce about quark matter in neutron stars in light of recent exciting developments in neutron star observations. We state the theoretical ideas underlying the equation of state of dense quark matter, including color superconducting quark matter. We also highlight recent advances stemming from re-examination of an old paradigm for the surface structure of quark stars and discuss possible evolutionary scenarios from neutron stars to quark stars, with emphasis on astrophysical observations.

Surface structure of quark stars with magnetic fields

We investigate the impact of magnetic fields on the electron distribution of the electrosphere of quark stars. For moderately strong magnetic fields of B ∼ 1013 G, quantization effects are generally weak due to the large number density of electrons at surface, but can nevertheless affect the photon emission properties of quark stars. We outline the main observational characteristics of quark stars as determined by their surface emission, and briefly discuss their formation in explosive events termed as quark-novae, which may be connected to the r-process.

Role of quark mass in cold and dense perturbative QCD

We consider the equation of state of QCD at high density and zero temperature in perturbation theory to first order in the coupling constant $\alpha_s$. We compute the thermodynamic potential including the effect of a non-vanishing mass for the strange quark and show that corrections are sizable. Renormalization group running of the coupling and the strange quark mass plays a crucial role. The structure of quark stars is dramatically modified.

Gluon condensates, quark matter equation of state and quark stars

We consider here quark matter equation of state including strange quarks and taking into account a nontrivial vacuum structure for QCD with gluon condensates. The parameters of condendsate function are determined from minimisation of the thermodynamic potential. The scale parameter of the gluon condensates is fixed from the SVZ parameter in the context of QCD sum rules at zero temperature and zero baryon density. The equation of state for strange matter at zero temperature as derived is used to study quark star structure using Tolman Oppenheimer Volkoff equations. Stable solutions for quark stars are obtained with a large Chandrasekhar limit as 3.2 $M_\odot$ and radii around 17 kms.