arXiv subjects

G. Abbas

Publications and source records attributed to G. Abbas.

At least 55 records · Page 3Linked to original sources

arXiv2015

Strange Stars in $f(T)$ Gravity With MIT Bag Model

This paper deals with existence of strange stars in $f\left(T\right) $ modified gravity. For this purpose, we have taken the diagonal tetrad field of static spacetime with charged anisotropic fluid and MIT bag model, which provide the linear relation between radial pressure and density of the matter. Further, the analysis of the resulting equations have been done by assuming the parametric form of the metric functions in term of the radial profiles with some unknown constant (introduced by Krori and Barua). By the matching of two metrices, unknown constant of the metric functions appear in terms of mass, radius and charge of the stars, the observed values of these quantities have been used for the detail analysis of the the derived model. We have discuss the regularity, anisotropy, energy conditions, stability and surface redshift of the model.

physics.gen-ph↗

arXiv2015

Anisotropic Strange Quintessence Stars in $f(R)$ Gravity

In this paper, we have formulated the new exact model of quintessence anisotropic star in $f(R)$ theory of gravity. The dynamical equations in $f(R)$ theory with the anisotropic fluid and quintessence field have been solved by using Krori-Barua solution. In this case, we have used the Starobinsky model of $f(R)$ gravity. We have determined that all the obtained solutions are free from central singularity and potentially stable. The observed values of mass and radius of the different strange stars PSR J 1614-2230, SAXJ1808.4-3658(SS1), 4U1820- 30, PSR J 1614-2230 have been used to calculate the values of unknown constants in Krori and Barua metric. The physical parameters like anisotropy, stability and redshift of the stars have been investigated in detail.

physics.gen-ph↗

arXiv2015

Shearfree Condition and dynamical Instability in $f(R,T)$ gravity

The implications of shearfree condition on instability range of anisotropic fluid in $f(R,T)$ are studied in this manuscript. A viable $f(R, T)$ model is chosen to arrive at stability criterion, where $R$ is Ricci scalar and $T$ is the trace of energy momentum tensor. The evolution of spherical star is explored by employing perturbation scheme on modified field equations and contracted Bianchi identities in $f(R, T)$. The effect of imposed shearfree condition on collapse equation and adiabatic index $Γ$ is studied in Newtonian and post-Newtonian regimes.

gr-qc↗

arXiv2015

Anisotropic Compact Stars in $f(G)$ Gravity

This paper is devoted to study the possibility of forming anisotropic compact stars in modified Gauss-Bonnet, namely called as $f(G)$ theory of gravity which is one of the strong candidates,responsible for the accelerated expansion of the universe. For this purpose, we have used analytical solution of Krori and Barua metric to the Einstein field equations with anisotropic form of matter and power law model of $f(G)$ gravity. To determine the unknown constants in Krori and Barua metric, we have used the sample of compact stars, 4$U$1820-30, Her X-1, SAX J 1808-3658. The physical behavior of these stars have been analyzed with the observational data. In this setting, we have checked all the regularity conditions and stability of the compact stars 4$U$1820-30, Her X-1, SAX J1808-3658.

gr-qc↗

arXiv2015

Collapsing Plane Symmetric Source with Heat Flux and Conformal Flatness

This paper deals with the study of collapsing plane symmetric source in the presence of heat flux. For this purpose, we have calculated the Einstein field equations as well as Weyl tensor components. The conditions for the conformal flatness have been determined. The interior source has been matched smoothly with the exterior geometry in single null coordinate. It has been found the pressure is balanced with the out going heat flux and the continuity of the masses in two regions has been noted. A simple new model of collapse has been proposed which satisfies flatness condition, also we have discussed the physical properties of the model. For our model, we have calculated the temperature profile by using the approximation scheme.

physics.gen-ph↗

arXiv2015

Gravitational Collapse and Expansion of Charged Anisotropic Cylindrical Source

In this paper, we have discussed the gravitational collapse and expansion of charged anisotropic cylindrically symmetric gravitating source. To this end, the generating solutions of Einstein-Maxwell field equations for the given source and geometry have been evaluated. We found the auxiliary solution of the filed equations, this solution involves a single function which generates two kinds of anisotropic solutions. Every solution can be expressed in terms of arbitrary function of time that has been chosen arbitrarily to fit the various astrophysical time profiles. The existing solutions predict gravitational collapse and expansion depending on the choice of initial data. Instead of base to base collapse, in the present case, wall to wall collapse of the cylindrical source has been investigated. We have found that the electromagnetic field is responsible for the enhancement of anisotropy in collapsing system.

physics.gen-ph↗

arXiv2015

Dynamics of Anisotropic Collapsing Spheres in Einstein Gauss-Bonnet Gravity

This paper is devoted to investigate the dynamics of the self gravitating adiabatic and anisotropic source in $5D$ Einstein Gauss-Bonnet gravity. To this end, the source has been taken as Tolman-Bondi model which preserve inhomogeneity in nature. The field equations, Misner-Sharp mass and dynamical equations have formulated in Einstein Gauss-Bonnet gravity in $5D$. The junction conditions have been explored between the anisotropic source and vacuum solution in Gauss-Bonnet gravity in detail. The Misner and Sharp approach has been applied to define the proper time and radial derivatives. Further, these helps to formulate general dynamical equations. The equations show that the mass of the collapsing system increases with the same amount as the effective radial pressure increases. The dynamical system preserve retardation which implies that system under-consideration goes to gravitational collapse.

physics.gen-ph↗

arXiv2015

Analytic models of Anisotropic Strange Stars in $f(T)$ Gravity with Off-diagonal tetrad

This paper is devoted to study the analytic models of anisotropic compact stars in $f(T)$ gravity (where $T$ is torsion scalar), with non-diagonal tetrad. By taking the anisotropic source inside the spherically symmetric star, the equations of motions have been derived in the context of $f(T)$ gravity. Krori and Barua metric which satisfies the physical requirement of a realistic star, has been applied to describe the compact objects like strange stars. We use the power law form of $f(T)$ model to determine explicit relations of matter variables. Further, we have found the anisotropic behavior, energy conditions, stability and surface redshift of stars. Using the masses and radii of 4$U$1820-30, Her X-1, SAX J 1808-3658, we have determined the constants involved in metric components. Finally we discuss the graphical behavior of the analytic description of strange star candiddates.

physics.gen-ph↗

arXiv2015

Anisotropic Compact Stars in $f(T)$ Gravity

This paper deals with the theoretical modeling of anisotropic compact stars in the framework of $f(T)$ theory of gravity, where $T$ is torsion scalar. To this end, we have used the exact solutions of Krori and Barua metric to a static spherically symmetric metric. The unknown constants involved in the Krori and Barua metric have been specified by using the masses and radii of compact stars 4$U$1820-30, Her X-1, SAX J 1808-3658. The physical properties of these stars have been analyzed in the framework of $f(T)$ theory. In this setting, we have checked the anisotropic behavior, regularity conditions, stability and surface redshift of the compact stars.

physics.gen-ph↗

arXiv2014

Cylindrically Symmetric Models of Anisotropic Compact Stars

In this paper we have discussed the possibility of forming anisotropic compact stars from cosmological constant as one of the competent candidates of dark energy with cylindrical symmetry. For this purpose, we have applied the analytical solution of Krori and Barua metric to a particular cylindrically symmetric spacetime. The unknown constants in Krori and Barua metric have been determined by using masses and radii of class of compact stars like 4$U$1820-30, Her X-1, SAX J 1808-3658. The properties of these stars have been analyzed in detail. In this setting the cosmological constant has been taken as a variable which depends on the radial coordinates. We have checked all the regularity conditions, stability and surface redshift of the compact stars 4$U$1820-30, Her X-1, SAX J 1808-3658.

gr-qc↗

arXiv2014

Dynamical Stability of Collapsing Stars in Einstein Gauss-Bonnet Gravity

This paper is devoted to study the stability/instability of the expansionfree self gravitating source in the framework of Einstein Gauss-Bonnet gravity. The source has been taken as Tolman-Bondi model which is homogenous in nature. The field equations as dynamical equations have been evaluated in Gauss-Bonnet gravity in five dimensions. The junction conditions as well as cavity evaluations equations have been explored in detail. The perturbation scheme of first order has been applied to dynamical as Einstein Gauss-Bonnet field equations. The concept of Newtonian as well post Newtonian approximation have been used to derive general dynamical stability equations. In general this equation represents the stability of the gravitating source. Some particular values of system parameters have been chosen to prove the concept of stability graphically. It has been mentioned that other than chosen the particular values of the parameters the stability of the system would be disturbed, hence it would leads to instability.

gr-qc↗

arXiv2014

Geodesic Study of Regular Hayward Black Hole

This paper is devoted to study the geodesic structure of regular Hayward black hole. The timelike and null geodesic have been studied explicitly for radial and non-radial motion. For timelike and null geodesic in radial motion there exists analytical solution, while for non-radial motion the effective potential has been plotted, which investigates the position and turning points of the particle. It has been found that massive particle moving along timelike geodesics path are dragged towards the BH and continues move around BH in particular orbits.

gr-qc↗

arXiv2014

Magnetohydrodynamic Viscous Flow Over a Shrinking Sheet With Second Order Slip Flow Model

In this paper, we investigate the magnetohydrodynamic viscous flow with second order slip flow model over a permeable shrinking surface. We have obtained the closed form of exact solution of Navier-Stokes equations by using similarity variable technique. The effects of slip, suction and magnetic parameter have been investigated in detail. The results show that there are two solution branches, namely lower and upper solution branch. The behavior of velocity and shear stress profiles for different values of slip, suction and magnetic parameters has been discussed through graphs.

physics.flu-dyn↗

arXiv2014

Cardy-Verlinde Formula of Non-Commutative Schwarzschild Black Hole

Few years ago, Setare \cite{1} has investigated the Cardy-Verlinde formula of non-commutative black hole obtained by non-commutativity of coordinates. In this paper, we apply the same procedure to a non-commutative black hole obtained by the co-ordinate coherent approch. The Cardy-Verlinde formula is entropy formula of conformal field theory in an arbitrary dimension. It relates the entropy of conformal filed theory to its total energy and Casimir energy. In this paper, we have calculated the total energy and Casimir energy of non-commutative Schwarzschild black hole and have shown that entropy of non-commutative Schwarzschild black hole horizon can be expressed in terms of Cardy-Verlinde formula.

physics.gen-ph↗

arXiv2014

Effects of Electromagnetic Field on The Collapse and Expansion of Anisotropic Gravitating Source

This paper is devoted to study the effects of electromagnetic on the collapse and expansion of anisotropic gravitating source. For this purpose, we have evaluated the generating solutions of Einstein-Maxwell field equations with spherically symmetric anisotropic gravitating source. We found that a single function generates the various anisotropic solutions. In this case every generating function involves an arbitrary function of time which can be chosen to fit several astrophysical time profiles. Two physical phenomenon occur, one is gravitational collapse and other is the cosmological expanding solution. In both cases electromagnetic field effects the anisotropy of the model. For collapse the anisotropy is increased while for expansion it deceases from maximum value to finite positive value. In case of collaps there exits two horizons like in case of Reissner-Nordstr$\ddot{o}$m metric.

gr-qc↗

arXiv2013

Collapse and Expansion of Anisotropic Plane Symmetric Source

This paper deals with the collapse and expansion of relativistic anisotropic self-gravitating source. The field equations for non-radiating and non-static plane symmetric anisotropic source have been evaluated. The non-radiating property of the fluid leads to evaluation of the metric functions. We have classified the dynamical behavior of gravitational source as expansion and collapse. The collapse in this case leads to the final stage without the formation of apparent horizons while such horizons exists in case of spherical anisotropic source. The matching of interior and exterior regions provides the continuity of masses over the boundary surface.

gr-qc↗

arXiv2013

Thermodynamics of Phantom Energy Accreting onto a Black Hole in Einstein-Power-Maxwell Gravity

In this paper, we investigate the phantom energy accretion onto 3D black hole formulated in Einstein-Power-Maxwell theory. We have presented the conditions for critical accretion of phantom energy onto black hole. Further, we discuss the thermodynamics of phantom energy accreting onto black hole and found that first law of thermodynamics is easily satisfied while second law and generalized second law of thermodynamics remain invalid and conditionally valid, respectively. The results for BTZ black hole can be recovered by taking Maxwellian contribution equal to zero.

gr-qc↗

arXiv2013

Dynamics of Charged Radiating Collapse in Modified Gauss-Bonnet Gravity

This paper deals with the dynamics of a shearfree charged radiating collapse in modified Gauss-Bonnet gravity. The field equations for shearfree spherical interior geometry of a charged dissipative star are formulated. To study the dynamical behavior of collapsing matter, we derive the dynamical as well as transport equations. We conclude that the gravitational force in modified Gauss-Bonnet gravity is much stronger as compared to general relativity which implies the increase in the rate of collapse. Finally, we study the effect of charge on the dynamics of collapse.

gr-qc↗