A generalized anisotropic model for super dense stars

2021 ◽  
pp. 2150070
Author(s):  
Joaquin Estevez-Delgado ◽  
Gabino Estevez-Delgado ◽  
Noel Enrique Rodríguez Maya ◽  
José Martínez Peña ◽  
Aurelio Tamez Murguía
Keyword(s):  
Radial Pressure ◽  
Compact Stars ◽  
Anisotropic Model ◽  
Speed Of Light ◽  
Matter Distribution ◽  
Sphere Model ◽  
Tangential Pressure ◽  
Relativistic Fluid ◽  
Causal Condition ◽  
Dense Stars

A static anisotropic relativistic fluid sphere model with regular geometry and finite hydrostatic functions is presented. In the interior of the sphere, the density, radial pressure and tangential pressure are positives, monotonically decreasing with increasing radius and the radial pressure vanishes at the surface of the matter distribution and is joined continuously to the exterior Schwarzschild’s solution at this surface. The speeds of the radial and tangential sound are positive and lower than the speed of light, that is, the causal condition is not violated, and also the behavior of these guarantees that the model is potentially stable. Furthermore, the range of the compactness ratio is characteristic of compact stars and it is shown that the effect of the anisotropy generates that the speed of the radial sound can behave as a function monotonically increasing or monotonically decreasing.

scholarly journals Conformally symmetric relativistic star

2017 ◽  
Vol 32 (08) ◽  
pp. 1750053 ◽  
Author(s):  
Farook Rahaman ◽  
Sunil D. Maharaj ◽  
Iftikar Hossain Sardar ◽  
Koushik Chakraborty
Keyword(s):  
Conformal Symmetry ◽  
Compact Object ◽  
Radial Pressure ◽  
Compact Stars ◽  
Energy Conditions ◽  
Anisotropic Pressure ◽  
Matter Distribution ◽  
Strong Energy ◽  
Principal Directions ◽  
The Masses

We investigate whether compact stars having Tolman-like interior geometry admit conformal symmetry. Taking anisotropic pressure along the two principal directions within the compact object, we obtain physically relevant quantities such as transverse and radial pressure, density and redshift function. We study the equation of state (EOS) for the matter distribution inside the star. From the relation between pressure and density function of the constituent matter, we explore the nature and properties of the interior matter. The redshift function and compactness parameter are found to be physically reasonable. The matter inside the star satisfies the null, weak and strong energy conditions. Finally, we compare the masses and radii predicted from the model with corresponding values in some observed stars.

A regular perfect fluid model for dense stars

2019 ◽  
Vol 34 (15) ◽  
pp. 1950115 ◽  
Author(s):  
Gabino Estevez-Delgado ◽  
Joaquin Estevez-Delgado ◽  
Jorge Mauricio Paulin-Fuentes ◽  
Nadiezhda Montelongo Garcia ◽  
Modesto Pineda Duran
Keyword(s):  
Perfect Fluid ◽  
Fluid Model ◽  
Einstein Equations ◽  
Compact Stars ◽  
Variable Pressure ◽  
Spherically Symmetric ◽  
Matter Distribution ◽  
Stellar Objects ◽  
Dense Stars ◽  
Decreasing Functions

We present an exact regular solution of Einstein equations for a static and spherically symmetric spacetime with a matter distribution of isotropic perfect fluid. The construction of the solution is realized assigning a regular potential [Formula: see text] and integrating the isotropic perfect fluid condition for the pressure. The resulting solution is physically acceptable, i.e. the geometry is regular and the hydrostatic variable pressure and density are positive regular monotonic decreasing functions, the speed of the sound is positive and smaller than the speed of the light. An important element of this solution is that its compactness value [Formula: see text] is in the characteristic range of compact stars, which makes a remarkable difference with other models with isotropic perfect fluid, this is [Formula: see text] so that we could represent compact stellar objects as neutron stars. In particular, for the maximum compactness of a star with a mass of [Formula: see text] the radius is [Formula: see text] and their central density [Formula: see text] is characteristic of compact stars.

A study of anisotropic compact stars in f(R,ϕ,X) theory of gravity

2021 ◽  
Author(s):  
Adnan Malik ◽  
Iftikhar Ahmad ◽  
Kiran
Keyword(s):  
Modified Gravity ◽  
Scalar Potential ◽  
Radial Pressure ◽  
Compact Stars ◽  
Energy Conditions ◽  
Kinetic Term ◽  
Spherically Symmetric ◽  
Tangential Pressure ◽  
Equilibrium Conditions ◽  
Pressure Equilibrium

In this paper, we investigate the behavior of anisotropic compact stars in generalized modified gravity, namely [Formula: see text] gravity, where [Formula: see text] represents the Ricci scalar, [Formula: see text] is the scalar potential function and [Formula: see text] is a kinetic term of [Formula: see text]. We consider the spherically symmetric spacetime to analyze the feasible exposure of compact stars. We observe the behavior of anisotropic compact stars which includes Her X1, SAX J 1808.4-3658 and 4U 1820-30. From the graphical evaluation of energy density, tangential pressure, radial pressure, equilibrium conditions, energy conditions, mass–radius relationship, compactness and stability analysis of compact stars, it is concluded that the behavior of candidates of compact stars is regular in [Formula: see text] gravity for the considered parameter.

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 Plausible families of compact objects with a nonlocal equation of state

2013 ◽  
Vol 91 (4) ◽  
pp. 328-336 ◽  
Author(s):  
H. Hernández ◽  
L.A. Núñez
Keyword(s):  
Equation Of State ◽  
Total Mass ◽  
Radial Pressure ◽  
Compact Objects ◽  
Einstein Equations ◽  
Matter Distribution ◽  
Nonlocal Equation ◽  
The Family ◽  
Model Independent ◽  
Physical Variables

We present the plausibility of some models emerging from an algorithm devised to generate a one-parameter family of interior solutions for the Einstein equations. We explore how their physical variables change as the family parameter varies. The models studied correspond to anisotropic spherical matter configurations having a nonlocal equation of state. This particular type of equation of state, with no causality problems, provides at a given point the radial pressure not only as a function of the density but as a functional of the enclosed matter distribution. We have found that there are several model-independent tendencies as the parameter increases: the equation of state tends to be stiffer and the total mass becomes half of its external radius. Profiting from the concept of cracking of materials in general relativity, we obtain that these models become more potentially stable as the family parameter increases.

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 A new class of analytical solutions describing anisotropic neutron stars in general relativity

2021 ◽  
pp. 2150091
Author(s):  
Jay Solanki ◽  
Bhashin Thakore
Keyword(s):  
General Relativity ◽  
Neutron Stars ◽  
Analytical Solutions ◽  
Radial Pressure ◽  
Compact Stars ◽  
Theory Of Relativity ◽  
Field Equations ◽  
Inherent Anisotropy ◽  
Anisotropic Matter ◽  
New Class

A new class of solutions describing analytical solutions for compact stellar structures has been developed within the tenets of General Relativity. Considering the inherent anisotropy in compact stars, a stable and causal model for realistic anisotropic neutron stars was obtained using the general theory of relativity. Assuming a physically acceptable nonsingular form of one metric potential and radial pressure containing the curvature parameter [Formula: see text], the constant [Formula: see text] and the radius [Formula: see text], analytical solutions to Einstein’s field equations for anisotropic matter distribution were obtained. Taking the value of [Formula: see text] as −0.44, it was found that the proposed model obeys all necessary physical conditions, and it is potentially stable and realistic. The model also exhibits a linear equation of state, which can be applied to describe compact stars.

scholarly journals Quintessences compact star with Durgapal potential

2020 ◽  
Vol 35 (17) ◽  
pp. 2050144 ◽  
Author(s):  
Gabino Estevez-Delgado ◽  
Joaquin Estevez-Delgado ◽  
Aurelio Tamez Murguía ◽  
Rafael Soto-Espitia ◽  
Arthur Cleary-Balderas
Keyword(s):  
Compact Star ◽  
Radial Pressure ◽  
State Equation ◽  
Central Density ◽  
Star Model ◽  
Tangential Pressure ◽  
State Equations ◽  
Ordinary Matter ◽  
Linear State ◽  
Anisotropic Pressures

A compact star model formed by quintessence and ordinary matter is presented, both sources have anisotropic pressures and are described by linear state equations, also the state equation of the tangential pressure for the ordinary matter incorporates the effect of the quintessence. It is shown that depending on the compactness of the star [Formula: see text] the constant of proportionality [Formula: see text] between the density of the ordinary matter and the radial pressure, [Formula: see text], has an interval of values which is consistent with the possibility that the matter is formed by a mixture of particles like quarks, neutrons and electrons and not only by one type of them. The geometry is described by the Durgapal metric for [Formula: see text] and each one of the pressures and densities is positive, finite and monotonic decreasing, as well as satisfying the condition of causality and of stability [Formula: see text], which makes our model physically acceptable. The maximum compactness that we have is [Formula: see text], so we can apply our solution considering the observational data of mass and radii [Formula: see text], [Formula: see text] km which generate a compactness [Formula: see text] associated to the star PSR J0348[Formula: see text]+[Formula: see text]0432. In this case, the interval of [Formula: see text] and its maximum central density [Formula: see text] and in the surface [Formula: see text] of the star are [Formula: see text] and [Formula: see text], respectively, meanwhile the central density of the quintessence [Formula: see text].

Dynamical instability of anisotropic homogeneous cylinder

2019 ◽  
Vol 35 (05) ◽  
pp. 2050009 ◽  
Author(s):  
M. Sharif ◽  
Qanitah Ama-Tul-Mughani
Keyword(s):  
Variational Principle ◽  
Characteristic Frequency ◽  
Radial Pressure ◽  
Baryon Number ◽  
Dynamical Instability ◽  
Tangential Pressure ◽  
Dynamical Equations ◽  
Anisotropic Matter ◽  
Cylindrically Symmetric ◽  
Homogeneous Cylinder

In this paper, we consider a non-static cylindrically symmetric self-gravitating system with anisotropic matter configuration and investigate its stability regions by using a homogenous model. We establish perturbed form of dynamical equations by using Eulerian and Lagrangian approaches. The conservation of baryon number is applied to obtain adiabatic index as well as perturbed pressure. A variational principle is used to find characteristic frequency which helps to compute the instability criteria. It is found that dynamical instability can be prevented till the radius of a cylinder exceeds the limit R[Formula: see text]18. We conclude that the system becomes unstable against radial oscillations as the radial pressure increases relative to tangential pressure.

Quintessence compact stars satisfying Karmarkar condition

2019 ◽  
Vol 97 (4) ◽  
pp. 374-381 ◽  
Author(s):  
G. Abbas ◽  
Shahid Qaisar ◽  
Wajiha Javed ◽  
W. Ibrahim
Keyword(s):  
Radial Pressure ◽  
Compact Stars ◽  
Field Equations ◽  
Anisotropic Parameter ◽  
Proposed Model ◽  
Second Derivatives ◽  
Metric Functions ◽  
The Stability ◽  
Quintessence Field ◽  
Derivatives Of

In this research article, the authors have presented the modelling of quintessence compact stars, which satisfies the Karmarkar conditions. For this purpose, we have formulated the set of Einstein field equations with the static metric, anisotropic perfect fluid, and quintessence field. The equation of state pr= αρ and Karmarkar condition have been used to solve the set of field equations. The unknown constant in the metric functions (appearing due to the Karmarkar conditions) have been found by matching the interior metric with the Schwarzschild exterior metric. The observed value of mass and radius of some well-known classes of stars has been used. The fluid variables density, radial and transverse pressures, and anisotropic parameter have been plotted graphically. The first and second derivatives of density and radial pressure have been evaluated to discuss the regularity of the model. The speed of sound for the radial and transverse directions determines the stability of the proposed model. Moreover, the redshift for the proposed model of the star has been discussed.

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