scholarly journals Nonlocal equation of state in anisotropic static fluid spheres in general relativity

2004 ◽  
Vol 82 (1) ◽  
pp. 29-51 ◽  
Author(s):  
H Hernández ◽  
L A Núñez
Keyword(s):  
Equation Of State ◽  
Radial Pressure ◽  
Spherically Symmetric ◽  
Density Profiles ◽  
Physical Conditions ◽  
Tangential Stresses ◽  
Nonlocal Equation ◽  
Static Fluid ◽  
Anisotropic Fluids ◽  
Fluid Spheres

We show that it is possible to obtain, at least certain regions within spherically symmetric static matter configurations, credible anisotropic fluids satisfying a nonlocal equation of state. This particular type of equation of state provides, at a given point, the radial pressure not only as a function of the density at that point, but its functional throughout the enclosed distribution. To establish the physical plausibility of the proposed family of solutions satisfying a nonlocal equation of state, we study the constraints imposed by the junction, energy, and some intuitive physical conditions. We show that these static fluids having this particular equation of state are "naturally" anisotropic in the sense that they satisfy, identically, the anisotropic Tolman–Oppenheimer–Volkov equation. We also show that it is possible to obtain physically plausible static anisotropic spherically symmetric matter configurations starting from known density profiles, and also for configurations where tangential pressures vanish. This very particular type of relativistic sphere with vanishing tangential stresses is inspired by some of the models proposed to describe extremely magnetized neutron stars (magnetars) during the transverse quantum collapse.

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.

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 Spherically symmetric dissipative anisotropic fluids: A general study

2004 ◽  
Vol 69 (8) ◽  
Author(s):  
L. Herrera ◽  
A. Di Prisco ◽  
J. Martin ◽  
J. Ospino ◽  
N. O. Santos ◽  
...  
Keyword(s):  
Spherically Symmetric ◽  
General Study ◽  
Anisotropic Fluids

Stability of generalized polytropic models

2019 ◽  
Vol 16 (04) ◽  
pp. 1950056
Author(s):  
I. Nazir ◽  
M. Azam
Keyword(s):  
Equation Of State ◽  
Local Density ◽  
Hydrostatic Equilibrium ◽  
Physical Parameters ◽  
Spherically Symmetric ◽  
Anisotropic Matter ◽  
Polytropic Equation ◽  
Density Perturbations ◽  
Radial Forces ◽  
The Stability

In this paper, we have investigated the stability of a spherically symmetric object with charged anisotropic matter by using the concept of cracking. The cracking is a very intuitive technique to check the stability which is based on the analysis of the radial forces that appear on the system due to perturbations taking it out of its equilibrium state. For this, we have applied and studied the effect of local density perturbations to the hydrostatic equilibrium equation and on all the physical parameters with generalized polytropic equation of state. It is found that some of the generalized polytropic models exhibit cracking.

Dark matter distribution in superthin galaxies

2020 ◽  
Vol 495 (4) ◽  
pp. 3722-3726
Author(s):  
Ilia Kalashnikov
Keyword(s):  
Dark Matter ◽  
Surface Density ◽  
Distribution Density ◽  
Spherically Symmetric ◽  
Matter Distribution ◽  
Galactic Disc ◽  
Density Profiles ◽  
Visible Matter ◽  
Simple Physical Model ◽  
Dark Matter Distribution

ABSTRACT This paper presents a new method of calculating dark matter density profiles for superthin axial symmetric galaxies without a bulge. This method is based on a simple physical model, which includes an infinitely thin galactic disc immersed in a spherically symmetric halo of dark matter. To obtain the desired distribution density, it suffices to know a distribution of visible matter surface density in a galaxy and a dependence of angular velocity on the radius. As a byproduct, the well-known expression, which reproduces surface density of a superthin galaxy expressed through a rotation law, was obtained.

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.

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