scholarly journals Stable and self-consistent compact star models in teleparallel gravity

2020 ◽  
Vol 80 (10) ◽  
Author(s):  
G. G. L. Nashed ◽  
S. Capozziello
Keyword(s):  
Compact Star ◽  
Vacuum Solution ◽  
Radial Pressure ◽  
Teleparallel Gravity ◽  
Compact Objects ◽  
Radial Coordinate ◽  
Model Parameters ◽  
Field Equations ◽  
Tetrad Field ◽  
Star Models

AbstractIn the framework of Teleparallel Gravity, we derive a charged non-vacuum solution for a physically symmetric tetrad field with two unknown functions of radial coordinate. The field equations result in a closed-form adopting particular metric potentials and a suitable anisotropy function combined with the charge. Under these circumstances, it is possible to obtain a set of configurations compatible with observed pulsars. Specifically, boundary conditions for the interior spacetime are applied to the exterior Reissner–Nordström metric to constrain the radial pressure that has to vanish through the boundary. Starting from these considerations, we are able to fix the model parameters. The pulsar $$\textit{PSR J 1614-2230}$$ PSR J 1614 - 2230 , with estimated mass $$M= 1.97 \pm 0.04\, M_{\circledcirc },$$ M = 1.97 ± 0.04 M ⊚ , and radius $$R= 9.69 \pm 0.2$$ R = 9.69 ± 0.2 km is used to test numerically the model. The stability is studied, through the causality conditions and adiabatic index, adopting the Tolman–Oppenheimer–Volkov equation. The mass–radius (M, R) relation is derived. Furthermore, the compatibility of the model with other observed pulsars is also studied. We reasonably conclude that the model can represent realistic compact objects.

scholarly journals Exact Axially Symmetric Solution inf(T)Gravity Theory

2014 ◽  
Vol 2014 ◽  
pp. 1-9 ◽  
Author(s):  
Gamal G. L. Nashed
Keyword(s):  
Vacuum Solution ◽  
Gravity Theory ◽  
Kerr Metric ◽  
Radial Coordinate ◽  
Lorentz Transformations ◽  
Axially Symmetric ◽  
Field Equations ◽  
Tetrad Field ◽  
Kerr Spacetime ◽  
Euler’S Angles

A general tetrad field with sixteen unknown functions is applied to the field equations off(T)gravity theory. An analytic vacuum solution is derived with two constants of integration and an angleΦthat depends on the angle coordinateϕand radial coordinater. The tetrad field of this solution is axially symmetric and the scalar torsion vanishes. We calculate the associated metric of the derived solution and show that it represents Kerr spacetime. Finally, we show that the derived solution can be described by two local Lorentz transformations in addition to a tetrad field that is the square root of the Kerr metric. One of these local Lorentz transformations is a special case of Euler’s angles and the other represents a boost when the rotation parameter vanishes.

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 Neutral physical compact spherically symmetric stars with non-exotic matters in Einstein’s cluster model using Weitzenböck geometry

2020 ◽  
Vol 80 (12) ◽  
Author(s):  
G. G. L. Nashed ◽  
Amare Abebe ◽  
Kazuharu Bamba
Keyword(s):  
Energy Momentum Tensor ◽  
Compact Star ◽  
Radial Pressure ◽  
Static Stability ◽  
Momentum Tensor ◽  
Field Equations ◽  
Tangential Pressure ◽  
Tetrad Field ◽  
Gravitational Field Equations ◽  
Anisotropic Energy

AbstractWe revisit the neutral (uncharged) solutions that describe Einstein’s clusters with matters in the frame of Weitzenböck geometry. To this end, we use a tetrad field with non-diagonal spherical symmetry which gives vanishing of the off-diagonal components of the gravitational field equations. The cluster solutions are calculated by using an anisotropic energy–momentum tensor. We solve the field equations using two novel assumptions. First, we use an equation of state that relates density with tangential pressure, and then we assume a specific form of one of the metric potentials in addition to the assumption of the vanishing of radial pressure to make the system of differential equations in a closed-form. The resulting solutions are coincide with the literature $$ however \, \,in\, \,this\, \,study\, \,we\, \,constrain\,\, the\,\, constants \, \,of\, \, integration\, \, from\, \, \,the\, \, matching\,\, of\, \,boundary $$ h o w e v e r i n t h i s s t u d y w e c o n s t r a i n t h e c o n s t a n t s o f i n t e g r a t i o n f r o m t h e m a t c h i n g o f b o u n d a r y $$ condition\, \, in a\,\, way \,\,different\,\, from\,\, that\,\, presented \,\,in \,\,the\,\, literature. $$ c o n d i t i o n i n a w a y d i f f e r e n t f r o m t h a t p r e s e n t e d i n t h e l i t e r a t u r e . Among many things presented in this study, we investigate the static stability specification and show that our model is consistent with a real compact start except that the tangential pressure has a vanishing value at the center of the star which is not accepted from the physical viewpoint of a real compact star. We conclude that the model that has vanishing radial pressure in the frame of Einstein’s theory is not a physical model. Therefore, we extend this study and derive a new compact star without assuming the vanishing of the redial pressure but instead we assume new form of the metric potentials. We repeat our procedure done in the case of vanishing radial pressure and show in details that the new compact star is more realistic from different physical viewpoints of real compact stellar.

scholarly journals A new class of anisotropic charged compact star

2017 ◽  
Vol 1 (5) ◽  
pp. 151-157
Author(s):  
Ratanpal BS ◽  
Bhar P
Keyword(s):  
Comparative Study ◽  
Closed Form ◽  
Compact Star ◽  
Radial Pressure ◽  
Graphical Analysis ◽  
Model Parameters ◽  
Field Equations ◽  
New Model ◽  
New Class ◽  
Suitable Form

A new model of charged compact star is reported by solving the Einstein-Maxwell field equations by choosing a suitable form of radial pressure. The model parameters ρ,pr,p⊥ and E2 are in closed form and all are well behaved inside the stellar interior. A comparative study of charged and uncharged model is done with the help of graphical analysis.

scholarly journals Spherically Symmetric Solution in (1+4)-Dimensionalf(T)Gravity Theories

2014 ◽  
Vol 2014 ◽  
pp. 1-8 ◽  
Author(s):  
Gamal G. L. Nashed
Keyword(s):  
Symmetric Solution ◽  
Vacuum Solution ◽  
Azimuthal Angle ◽  
Radial Coordinate ◽  
Spherically Symmetric ◽  
Field Equations ◽  
Tetrad Field ◽  
The Third ◽  
Special Vacuum ◽  
Spherically Symmetric Solution

A nondiagonal spherically symmetric tetrad field, involving four unknown functions of radial coordinaterplus an angleΦ, which is a generalization of the azimuthal angleϕ, is applied to the field equations of (1+4)-dimensionalf(T)gravity theory. A special vacuum solution with one constant of integration is derived. The physical meaning of this constant is shown to be related to the gravitational mass of the system and the associated metric represents Schwarzschild in (1+4)-dimension. The scalar torsion related to this solution vanishes. We put the derived solution in a matrix form and rewrite it as a product of three matrices: the first represents a rotation while the second represents an inertia and the third matrix is the diagonal square root of Schwarzschild spacetime in (1+4)-dimension.

Study of some compact objects in R + 2βT gravity

2019 ◽  
Vol 28 (16) ◽  
pp. 2040005
Author(s):  
Arfa Waseem ◽  
M. Sharif
Keyword(s):  
Stellar System ◽  
Graphical Analysis ◽  
Compact Objects ◽  
Stellar Structure ◽  
Energy Conditions ◽  
Spherically Symmetric ◽  
Field Equations ◽  
Star Models ◽  
Mit Bag Model ◽  
Text Model

The aim of this work is to examine the nature as well as physical characteristics of anisotropic spherically symmetric stellar candidates in the context of [Formula: see text] gravity. We assume that the fluid components such as pressure and energy density are related through MIT bag model equation-of-state in the interior of stellar system. In order to analyze the structure formation of some specific star models, the field equations are constructed using Krori–Barua solution in which the unknown constants are evaluated by employing observed values of radii and masses of the considered stars. We check the consistency of [Formula: see text] model through the graphical analysis of energy conditions as well as stability of stellar structure. It is found that our considered stars show viable as well as stable behavior for this model.

Charged compact objects in f(R,T) gravity

2019 ◽  
Vol 28 (02) ◽  
pp. 1950033 ◽  
Author(s):  
M. Sharif ◽  
Arfa Waseem
Keyword(s):  
Energy Density ◽  
Observational Data ◽  
Compact Star ◽  
Compact Objects ◽  
Energy Conditions ◽  
Star Models ◽  
Anisotropic Factor ◽  
Stellar Models ◽  
Stable Structures

This paper analyzes the effects of charge on the nature of relativistic compact star candidates with anisotropic distribution in the framework of [Formula: see text] gravity. For this purpose, we consider Krori–Barua solutions and obtain the values of unknown constants as well as charge using observational data of Her X-1, 4U1820-30 and SAX J 1808.4-3658 star models. For three viable [Formula: see text] models, we investigate the behavior of energy density, transverse as well as radial pressures in the interior geometry of these stars. The validity of energy conditions, effect of anisotropic factor and stability of these stellar models are also examined. We conclude that the effect of charge leads to more stable structures of relativistic compact objects.

Kerr–Newman solution in modified teleparallel theory of gravity

2014 ◽  
Vol 24 (01) ◽  
pp. 1550007 ◽  
Author(s):  
Gamal G. L. Nashed
Keyword(s):  
Azimuthal Angle ◽  
Polar Angle ◽  
Radial Coordinate ◽  
Lorentz Transformations ◽  
Square Root ◽  
Axially Symmetric ◽  
Field Equations ◽  
Tetrad Field ◽  
Teleparallel Theory ◽  
Theory Of Gravity

A nondiagonal tetrad field having six unknown functions plus an angle Φ, which is a function of the radial coordinate r, azimuthal angle θ and the polar angle ϕ, is applied to the charged field equations of modified teleparallel theory of gravity. A special nonvacuum solution is derived with three constants of integration. The tetrad field of this solution is axially symmetric and its scalar torsion is constant. The associated metric of the derived solution gives Kerr–Newman spacetime. We have shown that the derived solution can be described by a local Lorentz transformations plus a diagonal tetrad field that is the square root of the Kerr–Newman metric. We show that any solution of general relativity (GR) can be a solution in f(T) under certain conditions.

scholarly journals Generalized compact star models with conformal symmetry

2021 ◽  
Vol 81 (12) ◽  
Author(s):  
J. W. Jape ◽  
S. D. Maharaj ◽  
J. M. Sunzu ◽  
J. M. Mkenyeleye
Keyword(s):  
Compact Star ◽  
Conformal Symmetry ◽  
Compact Objects ◽  
Energy Conditions ◽  
Geometric Framework ◽  
Exact Model ◽  
Star Models ◽  
Special Cases ◽  
Physical Forces ◽  
The Stability

AbstractWe generate a new generalized regular charged anisotropic exact model that admits conformal symmetry in static spherically symmetric spacetime. Our model was examined for physical acceptability as realistic stellar models. The regularity is not violated, the energy conditions are satisfied, the physical forces balanced at equilibrium, the stability is satisfied via adiabatic index, and the surface red shift and mass–radius ratio are within the required bounds. Our conformal charged anisotropic exact solution contains models generated by Finch–Skea, Vaidya–Tikekar and Schwarzschild. Also, some recent charged or neutral and anisotropic or isotropic conformally symmetric models are found as special cases of our exact model. Our approach using a conformal symmetry provides a generalized geometric framework for studying compact objects.

scholarly journals Scalar perturbation potentials in a homogeneous and isotropic Weitzenböck geometry

2016 ◽  
Vol 25 (07) ◽  
pp. 1650087
Author(s):  
A. Behboodi ◽  
S. Akhshabi ◽  
K. Nozari
Keyword(s):  
Degrees Of Freedom ◽  
Teleparallel Gravity ◽  
Scalar Perturbation ◽  
Coordinate Frame ◽  
Field Equations ◽  
Tetrad Field ◽  
Cosmological Perturbation ◽  
Gauge Invariant ◽  
Teleparallel Theory ◽  
Perturbation Parameters

We describe the fully gauge invariant cosmological perturbation equations in teleparallel gravity by using the gauge covariant version of the Stewart lemma for obtaining the variations in tetrad perturbations. In teleparallel theory, perturbations are the result of small fluctuations in the tetrad field. The tetrad transforms as a vector in both its holonomic and anholonomic indices. As a result, in the gauge invariant formalism, physical degrees of freedom are those combinations of perturbation parameters which remain invariant under a diffeomorphism in the coordinate frame, followed by an arbitrary rotation of the local inertial (Lorentz) frame. We derive these gauge invariant perturbation potentials for scalar perturbations and present the gauge invariant field equations governing their evolution.

Sign in / Sign up

Export Citation Format

Share Document