scholarly journals Anisotropic stellar model of neutron stars in f(T) gravity with off-diagonal tetrad

2022 ◽  
Vol 82 (1) ◽  
Author(s):  
Jay Solanki ◽  
Jackson Levi Said
Keyword(s):  
Neutron Stars ◽  
Graphical Analysis ◽  
Quadratic Equation ◽  
Stellar Model ◽  
Compact Stars ◽  
Quadratic Model ◽  
Model Parameters ◽  
Stellar Objects ◽  
Wide Range ◽  
Quadratic Equation Of State

AbstractIn this paper, we develop a new class of analytical solutions describing anisotropic stellar structures of observed neutron stars using modified f(T) gravity. We use the off-diagonal tetrad that is best suitable for studying spherically symmetric objects in f(T) gravity. We develop exact solutions in the quadratic model of f(T) gravity by introducing physically reliable metric potentials that can describe a wide range of astrophysical systems. We then apply the model to investigate the stellar structures of four observed compact stars, 4U 1538-52, J0437-4715, J0030+0451, and 4U 1820-30. We calculate the values of model parameters for the stellar objects under examination in this paper. Comprehensive graphical analysis shows that the model describing anisotropic stellar structures is physically acceptable, causal, and stable. The model inherently exhibits the quadratic equation of state that can be utilized to investigate the material composition and stellar structures of the observed compact stars.

scholarly journals RELATIVISTIC STELLAR MODEL ADMITTING A QUADRATIC EQUATION OF STATE

2013 ◽  
Vol 22 (13) ◽  
pp. 1350074 ◽  
Author(s):  
R. SHARMA ◽  
B. S. RATANPAL
Keyword(s):  
Equation Of State ◽  
Analytic Solution ◽  
Geometric Interpretation ◽  
Quadratic Equation ◽  
Stellar Model ◽  
Model Parameters ◽  
Spherically Symmetric ◽  
Quadratic Equation Of State ◽  
Anisotropic Star

A class of solutions describing the interior of a static spherically symmetric compact anisotropic star is reported. The analytic solution has been obtained by utilizing the Finch and Skea [Class. Quantum Grav.6 (1989) 467] ansatz for the metric potential grr which has a clear geometric interpretation for the associated background spacetime. Based on physical grounds, appropriate bounds on the model parameters have been obtained and it has been shown that the model admits an equation of state (EOS) which is quadratic in nature.

scholarly journals Stability and improved physical characteristics of relativistic compact objects arising from the quadratic term in $$p_r = \alpha \rho ^2 + \beta \rho - \gamma $$

2021 ◽  
Vol 81 (1) ◽  
Author(s):  
S. Thirukkanesh ◽  
Robert S. Bogadi ◽  
Megandhren Govender ◽  
Sibusiso Moyo
Keyword(s):  
Equation Of State ◽  
Gravitational Potential ◽  
Equations Of State ◽  
Quadratic Equation ◽  
Physical Characteristics ◽  
Compact Objects ◽  
Quadratic Term ◽  
Stellar Objects ◽  
Quadratic Equation Of State ◽  
The Stability

AbstractWe investigate the stability and enhancement of the physical characteristics of compact, relativistic objects which follow a quadratic equation of state. To achieve this, we make use of the Vaidya–Tikekar metric potential. This gravitational potential has been shown to be suitable for describing superdense stellar objects. Pressure anisotropy is also a key feature of our model and is shown to play an important role in maintaining stability. Our results show that the combination of the Vaidya–Tikekar gravitational potential used together with the quadratic equation of state provide models which are favourable. In comparison with other equations of state, we have shown that the quadratic equation of state mimics the colour-flavour-locked equation of state more closely than the linear equation of state.

scholarly journals An analytical anisotropic compact stellar model of embedding class I

2021 ◽  
Vol 36 (05) ◽  
pp. 2150028
Author(s):  
Lipi Baskey ◽  
Shyam Das ◽  
Farook Rahaman
Keyword(s):  
Radial Pressure ◽  
Stellar Model ◽  
Compact Objects ◽  
Compact Stars ◽  
Model Parameters ◽  
Field Equations ◽  
Principal Stresses ◽  
Schwarzschild Solution ◽  
Spherical Fluid ◽  
Physical Profile

A class of solutions of Einstein field equations satisfying Karmarkar embedding condition is presented which could describe static, spherical fluid configurations, and could serve as models for compact stars. The fluid under consideration has unequal principal stresses i.e. fluid is locally anisotropic. A certain physically motivated geometry of metric potential has been chosen and codependency of the metric potentials outlines the formation of the model. The exterior spacetime is assumed as described by the exterior Schwarzschild solution. The smooth matching of the interior to the exterior Schwarzschild spacetime metric across the boundary and the condition that radial pressure is zero across the boundary lead us to determine the model parameters. Physical requirements and stability analysis of the model demanded for a physically realistic star are satisfied. The developed model has been investigated graphically by exploring data from some of the known compact objects. The mass-radius (M-R) relationship that shows the maximum mass admissible for observed pulsars for a given surface density has also been investigated. Moreover, the physical profile of the moment of inertia (I) thus obtained from the solutions is confirmed by the Bejger–Haensel concept.

scholarly journals The possibility of twin star solutions in a model based on lattice QCD thermodynamics

2021 ◽  
Vol 81 (1) ◽  
Author(s):  
P. Jakobus ◽  
A. Motornenko ◽  
R. O. Gomes ◽  
J. Steinheimer ◽  
H. Stoecker
Keyword(s):  
Neutron Stars ◽  
Lattice Qcd ◽  
Model Equation ◽  
Compact Stars ◽  
Model Parameters ◽  
Bag Model ◽  
First Order ◽  
Stellar Masses ◽  
First Order Phase

AbstractThe properties of compact stars and in particular the existence of twin star solutions are investigated within an effective model that is constrained by lattice QCD thermodynamics. The model is modified at large baryon densities to incorporate a large variety of scenarios of first order phase transitions to a phase of deconfined quarks. This is achieved by matching two different variants of the bag model equation of state, in order to estimate the role of the Bag model parameters on the appearance of a second family of neutron stars. The produced sequences of neutron stars are compared with modern constrains on stellar masses, radii, and tidal deformability from astrophysical observations and gravitational wave analyses. It is found that those scenarios in our analysis, in which a third family of stars appeared due to the deconfinement transition, are disfavored from astrophysical constraints.

scholarly journals Charged stars in 4D Einstein–Gauss–Bonnet gravity

2021 ◽  
Vol 81 (9) ◽  
Author(s):  
Ayan Banerjee ◽  
Sudan Hansraj ◽  
Lushen Moodly
Keyword(s):  
Graphical Analysis ◽  
Compact Objects ◽  
Gravity Theory ◽  
Compact Stars ◽  
Model Parameters ◽  
The Novel ◽  
Coupling Constant ◽  
Curvature Effects ◽  
New Exact Solutions ◽  
Local Gravity

AbstractAn alternative gravity theory that has attracted considerable attention recently is the novel four-dimensional Einstein–Gauss–Bonnet (4EGB) gravity. This idea was proposed to bypass the Lovelock’s theorem and to permit nontrivial higher curvature effects on the four-dimensional local gravity. In this approach, the Gauss–Bonnet (GB) coupling constant $$\alpha $$ α is rescaled by a factor of $$\alpha /(D -4)$$ α / ( D - 4 ) in D dimensions and taking the limit $$D \rightarrow 4$$ D → 4 . In this article, we analyze the effects of charge on static compact stars in the regularized 4D EGB gravity theory. Two classes of new exact solutions are found for a particular choice of the gravitational potential and assuming a relationship between the electric field intensity and the spatial potential. A graphical analysis indicates that the matter and electromagnetic variables are well behaved for specific values of the parameter space. Finally, based on physical grounds appropriate bounds on the model parameters we show that compact objects with the value of adiabatic index $$\gamma $$ γ is consistent with expectations.

A uniparametric perfect fluid solution to represent compact stars

2021 ◽  
Vol 36 (10) ◽  
pp. 2150068
Author(s):  
Joaquin Estevez-Delgado ◽  
Noel Enrique Rodríguez Maya ◽  
José Martínez Peña ◽  
David Rivera Rangel ◽  
Nancy Cambron Muñoz
Keyword(s):  
Neutron Stars ◽  
Perfect Fluid ◽  
Stellar Model ◽  
Compact Objects ◽  
Compact Stars ◽  
Index Formula ◽  
Perfect Fluid Solution ◽  
Gravitational Theories ◽  
State Formula ◽  
The Stability

In the description of neutron stars, it is very important to consider gravitational theories as general relativity, due to the determining influence on the behavior of the different types of stars, since some objects show densities even bigger than nuclear density. This paper starts with Einstein’s equations for a perfect fluid and then we present a uniparametric stellar model which allows to describe compact objects like neutron stars with compactness ratio [Formula: see text]. The pressure and density are monotone decreasing regular functions, the speed of sound satisfies the causality condition, while the value for its adiabatic index [Formula: see text] guarantees the stability. In addition, the graph of [Formula: see text] versus [Formula: see text] shows a quasi-linear relationship for the equation of state [Formula: see text], which is similar to the so-called MIT Bag equation when we have the interaction between quarks. In our case it is due to the interaction of the different components found inside the star, such as electrons and neutrons. As an application of the model, we describe the star PSR J1614-2230 with a observed mass of [Formula: see text] and a radius [Formula: see text], the model shows that the maximum central density occurs for a maximal compactness value [Formula: see text].

scholarly journals Compact stars with quadratic equation of state

2015 ◽  
Vol 357 (1) ◽  
Author(s):  
Sifiso A. Ngubelanga ◽  
Sunil D. Maharaj ◽  
Subharthi Ray
Keyword(s):  
Equation Of State ◽  
Quadratic Equation ◽  
Compact Stars ◽  
Quadratic Equation Of State

Strange quark mass effect on the structure of hybrid stars

2018 ◽  
Vol 27 (01) ◽  
pp. 1850006 ◽  
Author(s):  
Jian-Feng Xu ◽  
Yan-An Luo ◽  
Lei Li ◽  
Guang-Xiong Peng
Keyword(s):  
Quark Matter ◽  
Quark Mass ◽  
Strange Quark ◽  
Mass Effect ◽  
Compact Stars ◽  
Model Parameters ◽  
Maximum Mass ◽  
Strange Quark Mass ◽  
Wide Range ◽  
Hybrid Stars

We study the strange quark mass effect on the phase diagram of strong interaction and the structure of compact stars with a thermodynamically enhanced perturbative QCD model by matching quark matter onto nuclear matter using the Gibbs conditions. It is found that the mass effect of strange quark matter can obviously stiffen the equation of state of mixed phases and result in more massive hybrid stars (HSs), while that usually lowers the maximum mass of pure quark stars. Given reasonable model parameters, the maximum mass of HSs can reach two times the solar mass and the stars always have mixed-phase core in a considerably wide range of model parameters.

scholarly journals Model of the Phase Transition Mimicking the Pasta Phase in Cold and Dense Quark-Hadron Matter

2018 ◽  
Vol 173 ◽  
pp. 03003 ◽  
Author(s):  
Alexander Ayriyan ◽  
Hovik Grigorian
Keyword(s):  
Phase Transition ◽  
Neutron Stars ◽  
Quark Matter ◽  
Mixed Phase ◽  
Compact Stars ◽  
Phase Model ◽  
Model Parameters

A simple mixed phase model mimicking so-called “pasta” phases in the quarkhadron phase transition is developed and applied to static neutron stars for the case of DD2 type hadronic and NJL type quark matter models. The influence of the mixed phase on the mass-radius relation of the compact stars is investigated. Model parameters are chosen such that the results are in agreement with the mass-radius constraints.

scholarly journals Supermassive neutron stars in axion F(R) gravity

2020 ◽  
Vol 493 (1) ◽  
pp. 78-86 ◽  
Author(s):  
Artyom V Astashenok ◽  
Sergey D Odintsov
Keyword(s):  
Equation Of State ◽  
Neutron Stars ◽  
Scalar Curvature ◽  
Equations Of State ◽  
Compact Stars ◽  
Axion Mass ◽  
Axion Field ◽  
Wide Range ◽  
Star Surface ◽  
Effective Contribution

ABSTRACT We investigated realistic neutron stars in axion R2 gravity. The coupling between curvature and axion field ϕ is assumed in the simple form ∼R2ϕ. For the axion mass in the range ma ∼ 10−11–10−10 eV the solitonic core within neutron star and corresponding halo with size ∼100 km can exist. Therefore the effective contribution of R2 term grows inside the star and it leads to change of star parameters (namely, mass, and radius). We obtained the increase of star mass independent from central density for wide range of masses. Therefore, maximal possible mass for given equation of state grows. At the same time, the star radius increases not so considerably in comparison with GR. Hence, our model may predict possible existence of supermassive compact stars with masses $M\sim 2.2\!-\!2.3\, \mathrm{M}_\odot$ and radii Rs ∼ 11 km for realistic equation of state (we considered APR equation of state). In general relativity one can obtain neutron stars with such characteristics only for unrealistic, extremely stiff equations of state. Note that this increase of mass occurs due to change of solution for scalar curvature outside the star. In GR curvature drops to zero on star surface where ρ = p = 0. In the model underconsideration the scalar curvature dumps more slowly in comparison with vacuum R2 gravity due to axion ‘galo’ around the star.

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