c © World Scientific Publishing Company Anisotropic Compact stars with variable cosmological constant (original) (raw)
Related papers
ANISOTROPIC COMPACT STARS WITH VARIABLE COSMOLOGICAL CONSTANT
International Journal of Modern Physics D, 2012
Recently the small value of the cosmological constant and its ability to accelerate the expansion of the Universe is of great interest. We discuss the possibility of forming of anisotropic compact stars from this cosmological constant as one of the competent candidates of dark energy. For this purpose we consider the analytical solution of Krori and Barua metric. We take the radial dependence of cosmological constant and check all the regularity conditions, TOV equations, stability and surface redshift of the compact stars. It has been shown as conclusion that this model is valid for any compact star and we have cited 4U 1820 − 30 as a specific example of that kind of star.
Anisotropic Compact Stars in f(R)f(R)f(R) Gravity
In this paper we have investigated the possibility of forming of anisotropic compact stars in f(R)f(R)f(R) gravity, one of the competent candidates of dark energy. To this end, we have applied the analytical solution of Krori and Barua metric to a static spherically symmetric spacetime in f(R)f(R)f(R) gravity. The unknown constants in Krori and Barua metric have been determined by using masses and radii of class of compact stars like 4$U$1820-30, Her X-1, SAX J 1808-3658. The properties of these stars have been analyzes in detail. Furthermore, we have checked the regularity conditions, energy conditions, anisotropic behavior, stability and surface redshift of the compact stars 4$U$1820-30, Her X-1, SAX J 1808-3658.
On Anisotropic Dark Energy Stars
arXiv (Cornell University), 2008
Anisotropic pressure dark energy stars are recently proposed as an alternative model to gravastar. However, the nature's classification of the fluid was based on the interval of the parameter omega\omegaomega, defined by the state equation that comes directly from the isotropic pressure Friedmann cosmological models. This procedure is not correct. In this work we propose a generalization of the limits of the parameter omega\omegaomega of the equation of state, for the case of anisotropic fluids.
Astrophysics and Space Science, 2011
A model of compact object coupled to inhomogeneous anisotropic dark energy is studied. It is assumed a variable dark energy that suffers a phase transition at a critical density. The anisotropic Λ-Tolman-Oppenheimer-Volkoff equations are integrated to know the structure of these objects. The anisotropy is concentrated on a thin shell where the phase transition takes place, while the rest of the star remains isotropic. The family of solutions obtained depends on the coupling parameter between the dark energy and the fermionic matter. The solutions share several features in common with the gravastar model. There is a critical coupling parameter that gives non-singular black hole solutions. The mass-radius relations are studied as well as the internal structure of the compact objects. The hydrodynamic stability of the models is analyzed using a standard test from the mass-radius relation. For each permissible value of the coupling parameter there is a maximum mass, so the existence of black holes is unavoidable within this model.
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 masses and radii of compact stars, 4U 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 the compact stars 4U 1820-30, Her X-1, SAX J 1808-3658.
Well behaved anisotropic compact star models in general relativity
Astrophysics and Space Science, 2016
Anisotropic compact star models have been constructed by assuming a particular form of a metric function e λ. We solved the Einstein field equations for determining the metric function e ν. For this purpose we have assumed a physically valid expression of radial pressure (p r). The obtained anisotropic compact star model is representing the realistic compact objects such as PSR 1937 +21. We have done an extensive study about physical parameters for anisotropic models and found that these parameters are well behaved throughout inside the star. Along with these we have also determined the equation of state for compact star which gives the radial pressure is purely the function of density i.e. p r = f (ρ).
Relativistic compact stellar model describing anisotropic stars
University of North Bengal, 2021
In this paper, we have derived a class of analytical solutions of Einstein fi eld equations for a spherically symmetric anisotropic matter distribution. By choosing one of the metric potentials grr to be Krori-Barua metric type and a specific choice of anisotropy we obtain the other metric function. The interior solutions thus obtained has been utilized to construct a potentially stable model that could describe compact stellar objects. The exterior vacuum region has been assigned with the Schwarzschild spacetime metric. Across the boundary of the compact star where the radial pressure drops to zero, the interior metric has been matched smoothly wit h the exterior metric to fix t he model parameters associated with t he solutions. All the regularity conditions, energy conditions and all other physical requirements demanded for a realistic compact system has been shown to satisfy graphically with this model corresponding to the pulsars 4U1820-30 (Mass= l.58M0 and radius= 9.1 km) [1] and Gen X-3 (Mass= l.49M0 and radius= 10.136 km)[2]. The stability of the model is also discussed using some of the known stability criterion namely TOV equation, adiabatic index, Buchdahl condition and Herrera's cracking concept etc. The wide applicability of our developed model has been justified with the numerical values of current observational data set from various other known compact stars to a high degree of accuracy.
Anisotropic models for compact stars
The European Physical Journal C, 2015
In the present paper we obtain an anisotropic analog of the Durgapal and Fuloria (Gen Relativ Gravit 17:671, 1985) perfect fluid solution. The methodology consists of contraction of the anisotropic factor with the help of both metric potentials e ν and e λ. Here we consider e λ the same as Durgapal and Fuloria (Gen Relativ Gravit 17:671, 1985) did, whereas e ν is as given by Lake (Phys Rev D 67:104015, 2003). The field equations are solved by the change of dependent variable method. The solutions set mathematically thus obtained are compared with the physical properties of some of the compact stars, strange star as well as white dwarf. It is observed that all the expected physical features are available related to the stellar fluid distribution, which clearly indicates the validity of the model.
Generalized relativistic anisotropic models for compact stars
arXiv: General Relativity and Quantum Cosmology, 2015
We present new anisotropic generalization of Buchdahl [1] type perfect fluid solution by using the method of earlier work [2]. In similar approach we have constructed the new pressure anisotropy factor Delta{\Delta}Delta by the help both the metric potential elambdae^{\lambda}elambda and enue^{\nu}enu. The metric potential elambdae^{\lambda}elambda same as Buchdahl [1] and enue^{\nu}enu is monotonic increasing function as suggested by Lake [3]. After that we obtain new well behaved general solution for anisotropic fluid distribution. We calculated the physical quantities like energy density, radial and tangential pressures, velocity of sound and red-shift etc. We observe that these quantities are positive and finite inside the compact star. Also note that mass and radius of our models can represent the structure of realistic astrophysical objects such as like Her X-1 and RXJ1856-37.
Dark Energy Stars with Quadratic Equation of State
www.preprints.org, 2019
Recent astronomical observations with respect to measurements in distant supernovas, cosmic microwave background and weak gravitational lensing confirm that the Universe is undergoing a phase of accelerated expansion and it has been proposed that this cosmological behavior is caused by a hypothetical dark energy which has a strong negative pressure that allows explain the expanding universe. Several theoretical ideas and models related dark the energy includes the cosmological constant, quintessence, Chaplygin gas, braneworld and tachyonic scalar fields. In this paper, we have obtained new relativistic stellar configurations considering an anisotropic fluid distribution with a charge distribution which could represents a potential model of a dark energy star. In order to investigate the effect of a quadratic equation of state in this anisotropic model we specify particular forms for the gravitational potential that allow solving the Einstein-Maxwell field equations. For these new solutions we checked that the radial pressure, metric coefficients, energy density, anisotropy factor, charge density , mass function are well defined and are regular in the interior of the star. The solutions found can be used in the development of dark energy stars models satisfying all physical acceptability conditions but the causality condition and strong energy condition are violated. We expect that these models have multiple applications in astrophysics and cosmology.