scholarly journals Some New Models of Strange Stars in 5-D Einstein-Gauss-Bonnet Gravity

2021 ◽  
Author(s):  
Manuel Malaver ◽  
Hamed Daei Kasmaei
Keyword(s):  
Equation Of State ◽  
Energy Density ◽  
Nonlinear Equation ◽  
Radial Pressure ◽  
Compact Stars ◽  
Coupling Constant ◽  
Strange Stars ◽  
Bonnet Gravity ◽  
New Models ◽  
Linear And Nonlinear

In this paper, we present some new models for anisotropic compact stars within the framework of 5-dimensional Einstein-Gauss-Bonnet (EGB) gravity with a linear and nonlinear equation of state considering a metric potential proposed for Thirukkanesh and Ragel (2012) and generalized for Malaver (2014). The new obtained models satisfy all physical requirements of a physically reasonable stellar object. Variables as energy density, radial pressure and the anisotropy are dependent of the values of the Gauss-Bonnet coupling constant

scholarly journals Quadrupole moments of rotating compact stars

2012 ◽  
Vol 8 (S291) ◽  
pp. 536-536
Author(s):  
Martin Urbanec ◽  
John Miller ◽  
Zdenek Stuchlik
Keyword(s):  
Neutron Star ◽  
Equation Of State ◽  
Neutron Stars ◽  
Strange Star ◽  
Compact Stars ◽  
Quadrupole Moments ◽  
Strange Stars

AbstractWe present quadrupole moments of rotating neutron and strange stars calculated using standard Hartle Thorne approach. We demonstrate differences between neutron and strange star parameters connected with quadrupole moments and how this parameters could be, in the case of neutron stars, approximated almost independently on neutron star equation of state.

Charged anisotropic static cylindrically symmetric models

2013 ◽  
Vol 91 (2) ◽  
pp. 113-119 ◽  
Author(s):  
M. Sharif ◽  
H. Ismat Fatima
Keyword(s):  
Electromagnetic Field ◽  
Equation Of State ◽  
Energy Density ◽  
Symmetric Space ◽  
Radial Pressure ◽  
Matter Distribution ◽  
Field Equations ◽  
Stellar Objects ◽  
Cylindrically Symmetric ◽  
Barotropic Equation

In this paper, we investigate exact solutions of the field equations for charged, anisotropic, static, cylindrically symmetric space–time. We use a barotropic equation of state linearly relating the radial pressure and energy density. The analysis of the matter variables indicates a physically reasonable matter distribution. In the most general case, the central densities correspond to realistic stellar objects in the presence of anisotropy and charge. Finally, we conclude that matter sources are less affected by the electromagnetic field.

scholarly journals 2+1 flavors QCD equation of state at zero temperature within Dyson–Schwinger equations

2015 ◽  
Vol 30 (36) ◽  
pp. 1550217 ◽  
Author(s):  
Shu-Sheng Xu ◽  
Yan Yan ◽  
Zhu-Fang Cui ◽  
Hong-Shi Zong
Keyword(s):  
Phase Transitions ◽  
Equation Of State ◽  
Energy Density ◽  
Chemical Potential ◽  
Compact Stars ◽  
Zero Temperature ◽  
Number Density ◽  
Charge Neutrality ◽  
Quark Number ◽  
Research Fields

Within the framework of Dyson–Schwinger equations (DSEs), we discuss the equation of state (EOS) and quark number densities of 2+1 flavors, that is to say, [Formula: see text], [Formula: see text], and [Formula: see text] quarks. The chemical equilibrium and electric charge neutrality conditions are used to constrain the chemical potential of different quarks. The EOS in the cases of 2 flavors and 2+1 flavors are discussed, and the quark number densities, the pressure, and energy density per baryon are also studied. The results show that there is a critical chemical potential for each flavor of quark, at which the quark number density turns to nonzero from 0; and furthermore, the system with 2+1 flavors of quarks is more stable than that with 2 flavors in the system. These discussions may provide some useful information to some research fields, such as the studies related to the QCD phase transitions or compact stars.

A New Model for Charged Anisotropic Matter with Modified Chaplygin Equation of State

2020 ◽  
Author(s):  
Manuel Malaver ◽  
Hamed Daei Kasmaei
Keyword(s):  
Equation Of State ◽  
Energy Density ◽  
Compact Star ◽  
Radial Pressure ◽  
Extended Version ◽  
Matter Distribution ◽  
Field Equations ◽  
New Model ◽  
Anisotropic Matter ◽  
Chaplygin Equation

In this paper, we found a new model for compact star with charged anisotropic matter distribution considering an extended version of the Chaplygin equation of state. We specify a particular form of the metric potential Z(x) that allows us to solve the Einstein-Maxwell field equations. The obtained model satisfies all physical properties expected in a realistic star such that the expressions for the radial pressure, energy density, metric coefficients, measure of anisotropy and the mass are fully well defined and are regular in the interior of star. The solution obtained in this work can have multiple applications in astrophysics and cosmology.

scholarly journals Relativistic Cowling approximation for fluid oscillation modes of color superconducting self-bound stars

2012 ◽  
Vol 8 (S291) ◽  
pp. 451-451
Author(s):  
German Lugones ◽  
Cesar Vasquez Flores
Keyword(s):  
Equation Of State ◽  
Gravitational Waves ◽  
Internal Structure ◽  
Quark Matter ◽  
Normal Modes ◽  
Pressure Oscillation ◽  
Compact Stars ◽  
Color Superconductivity ◽  
Strange Stars ◽  
Oscillation Modes

AbstractThe investigation of the quasi-normal modes of oscillation of compact stars can reveal much information about their equation of state and internal structure mainly through the analysis of the expected emission of gravitational waves. In this work we study non-radial oscillation modes of strange stars consisting of color superconducting quark matter. We focus on the fundamental and pressure oscillation modes within the frame of the Cowling approximation. We discuss the observable features that may allow a differentiation among hadronic stars, strange stars, and strange stars with color superconductivity.

scholarly journals Stellar hydrostatic equilibrium compact structures in f(𝒢,T) gravity

2019 ◽  
Vol 34 (05) ◽  
pp. 1950038 ◽  
Author(s):  
M. Farasat Shamir ◽  
Mushtaq Ahmad
Keyword(s):  
Energy Density ◽  
Neutron Stars ◽  
Gravity Model ◽  
Fluid Pressure ◽  
Stellar Mass ◽  
Hydrostatic Equilibrium ◽  
Compact Stars ◽  
Equilibrium Equations ◽  
Strange Stars ◽  
State Models

In this paper, stellar hydrostatic equilibrium configuration of the compact stars (neutron stars and strange stars) has been studied for [Formula: see text] gravity model, with [Formula: see text] and [Formula: see text] being the Gauss–Bonnet invariant and the trace of energy–momentum tensor, respectively. After deriving the hydrostatic equilibrium equations for [Formula: see text] gravity, the fluid pressure for the neutron stars and the strange stars has been computed by implying two equation of state models corresponding to two different compact stars. For the [Formula: see text] gravity model, with [Formula: see text], [Formula: see text], and [Formula: see text] being some specific parameters, substantial change in the behavior of the physical attributes of the compact stars like the energy density, pressure, stellar mass, and total radius has been noted with the corresponding change in [Formula: see text] values. Meanwhile, it has been shown that for some fixed central energy density and with increasing values of [Formula: see text], the stellar mass both for the neutron stars and the strange stars increases, while the total stellar radius [Formula: see text] exhibits the opposite behavior for both of the compact stars. It is concluded that for this [Formula: see text] stellar model, the maximum stellar mass can be boosted above the observational limits.

SELF-LENSING EFFECTS FOR COMPACT STARS AND THEIR MASS–RADIUS RELATION

2004 ◽  
Vol 19 (32) ◽  
pp. 2431-2435
Author(s):  
A. R. PRASANNA ◽  
SUBHARTHI RAY
Keyword(s):  
General Relativity ◽  
Neutron Star ◽  
Equation Of State ◽  
Quark Matter ◽  
Strange Quark ◽  
Strange Quark Matter ◽  
Compact Stars ◽  
Strange Stars ◽  
Lensing Effect ◽  
R Relation

During the last couple of years astronomers and astrophysicists have been debating on the fact whether the so-called "strange stars" — stars made up of strange quark matter, have been discovered with the candidates like SAX J1808.4–3658, 4U 1728–34, RX J1856.5–3754, etc. The main contention has been the estimation of radius of the star for an assumed mass of ~ 1.4 M⊙ and to see whether the point overlaps with the graphs for the neutron star equation of state or whether it goes to the region of stars made of strange matter equation of state. Using the well-established formulae from general relativity for the gravitational redshift and the "lensing effect" due to bending of photon trajectories, we, in this letter, relate the parameters M and R with the observable parameters, the redshift z and the radiation radius R∞, thus constraining both M and R for specific ranges, without any other arbitrariness. With the required inputs from observations, one ought to incorporate the effects of self-lensing of the compact stars which has been otherwise ignored in all of the estimations done so far. Nonetheless, these effects of self-lensing make a marked difference for constraints on the M–R relation.

scholarly journals Model of Charged Anisotropic Strange Stars in Minimally Coupled f R Gravity

2021 ◽  
Vol 2021 ◽  
pp. 1-25
Author(s):  
H. Nazar ◽  
G. Abbas
Keyword(s):  
Energy Density ◽  
Graphical Representation ◽  
Radial Pressure ◽  
Mass Function ◽  
Compact Stars ◽  
Energy Conditions ◽  
Anisotropic Fluid ◽  
Field Equations ◽  
Strange Matter ◽  
New Family

In the present article, we have investigated a new family of nonsingular solutions of static relativistic compact sphere which incorporates the characteristics of anisotropic fluid and electromagnetic field in the context of minimally coupled f R theory of gravity. The strange matter MIT bag model equation of state (EoS) has been considered along with the usual forms of the Karori–Barua KB metric potentials. For this purpose, we derived the Einstein–Maxwell field equations in the assistance of strange matter EoS and KB type ansatz by employing the two viable and cosmologically well-consistent models of f R = R + γ R 2 and f R = R + γ R R + α R 2 . Thereafter, we have checked the physical acceptability of the proposed results such as pressure, energy density, energy conditions, TOV equation, stability conditions, mass function, compactness, and surface redshift by using graphical representation. Moreover, we have investigated that the energy density and radial pressure are nonsingular at the core or free from central singularity and always regular at every interior point of the compact sphere. The numerical values of such parameters along with the surface density, charge to radius ratio, and bag constant are computed for three well-known compact stars such as CS1 SAXJ 1808 . 4 − 3658 ( x ˜ = 7.07   km , CS2 VelaX − 1 x ˜ = 9.56   km , and CS3 4U1820 − 30 x ˜ = 10   km and are presented in Tables 1–6. Conclusively, we have noticed that our presented charged compact stellar object in the background of two well-known f R models obeys all the necessary conditions for the stable equilibrium position and which is also perfectly fit to compose the strange quark star object.

f(T) gravity and static wormhole solutions

2014 ◽  
Vol 29 (27) ◽  
pp. 1450137 ◽  
Author(s):  
Muhammad Sharif ◽  
Shamaila Rani
Keyword(s):  
Equation Of State ◽  
Energy Density ◽  
Radial Pressure ◽  
Energy Conditions ◽  
Spherically Symmetric ◽  
Shape Functions ◽  
Field Equations ◽  
Torsion Scalar ◽  
Transverse Pressure

In this paper, we study static spherically symmetric wormhole solutions in the framework of f(T) gravity, where T represents torsion scalar. We consider non-diagonal tetrad and anisotropic distribution of the fluid. We construct expressions for matter components such as energy density, radial pressure and transverse pressure from the field equations. Taking into account a particular equation of state (EoS) in terms of traceless fluid, we discuss the behavior of energy conditions for wormhole solutions with well-known f(T) and shape functions. We conclude that physically acceptable static wormhole solutions are obtained for both these functions.

scholarly journals Dynamical system analysis of FLRW models with Modified Chaplygin gas

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Ali Osman Yılmaz ◽  
Ertan Güdekli
Keyword(s):  
Dynamical System ◽  
Equation Of State ◽  
Energy Density ◽  
System Analysis ◽  
Chaplygin Gas ◽  
Modified Chaplygin Gas ◽  
State Spaces ◽  
The Universe ◽  
Matter Energy ◽  
Far Future

AbstractWe investigate Friedmann–Lamaitre–Robertson–Walker (FLRW) models with modified Chaplygin gas and cosmological constant, using dynamical system methods. We assume $$p=(\gamma -1)\mu -\dfrac{A}{\mu ^\alpha }$$ p = ( γ - 1 ) μ - A μ α as equation of state where $$\mu$$ μ is the matter-energy density, p is the pressure, $$\alpha$$ α is a parameter which can take on values $$0<\alpha \le 1$$ 0 < α ≤ 1 as well as A and $$\gamma$$ γ are positive constants. We draw the state spaces and analyze the nature of the singularity at the beginning, as well as the fate of the universe in the far future. In particular, we address the question whether there is a solution which is stable for all the cases.

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