Anisotropic Compact Stars Research Articles

Study of anisotropic compact stars by exploring tidal deformability

In this paper, the effect of anisotropy on the tidal deformability of a compact neutron star is investigated. In particular, it is possible to quantify the tidal Love number, which is defined by tidal deformability. Tidal Love number provides the estimation of the tidal deformability of the binary system in response to the external gravitational field. The effect of anisotropy and compactness factor on the tidal Love number has been examined for a specific class of solutions that describes an anisotropic compact object.

Compact star in f(T) gravity with Tolman–Kuchowicz metric potential

Employing $f(T)$ gravity, where $T$ is the torson, we have developed a new model of an anisotropic compact star in this work. Tolman-Kuchowicz (TK) metric potential has been used to solve the set of field equations. Furthermore, the matching conditions for interior and exterior geometry have been discussed. We have considered observation data of the compact star LMC X-4 and analyzed thermodynamical properties (density, pressure, equation of state parameter, square speed of sound, and equilibrium condition) analytically and graphically to test the validity of the solution. The compact star is found to meet the energy conditions. Through the causality condition and Herrera's cracking concept, the stability analysis of the present model has been presented and it confirms the physical acceptability of the solution. It has been shown that the obtained interior solutions for compact stars are consistent with all necessary physical criterions and therefore relevant as well as physically acceptable.

Compact objects admitting Finch–Skea symmetry in [formula omitted] gravity

This paper investigates the viability and stability of anisotropic compact stars in the framework of f(R,T2) theory (R is the Ricci scalar and T2=TτυTτυ). In this perspective, we use Finch–Skea symmetry and consider different f(R,T2) models to examine physical characteristics of compact stars. We match interior spacetime with the exterior region to find the values of unknown constants. Further, we analyze the behavior of several physical quantities such as effective matter variables, energy bounds, anisotropic factor and equation of state parameters in the interior of Vela X-1, SAX J 1808.4-3658, Her X-1 and PSR J0348+0432 stars. The equilibrium state of these compact stars is examined through the Tolman–Oppenheimer–Volkoff equation and their stability is checked by causality condition, Herrera cracking approach and adiabatic index. It is found that all the required conditions are fulfilled for the considered models. We can conclude that more viable and stable compact stars are obtained in this modified theory.

Anisotropic compact stars in complexity formalism and isotropic stars made of anisotropic fluid under minimal geometric deformation (MGD) context in f(mathscr {T}) gravity-theory

In this paper, we present an anisotropic solution for static and spherically symmetric self-gravitating systems by demanding the vanishing of the complexity factor (Herrera in Phys Rev D 97:044010, 2018) along with the isotropization technique through the gravitational decoupling (GD) approach (Ovalle in Phys Rev D 95:104019, 2017) in f(mathscr {T})-gravity theory. We begin by implementing gravitational decoupling via MGD scheme as the generating mechanism to obtain anisotropic solutions describing physically realizable static, spherical self-gravitating systems. We adopt the Krori–Barua ansatz and present two new classes of stellar solutions: the minimally deformed anisotropic solution with a vanishing complexity factor and the isotropic solution via gravitational decoupling. We demonstrate that both classes of solutions obey conditions of regularity, causality and stability. An interesting feature is the switch in trends of some of the thermodynamical quantities such as effective density, radial and transverse stresses at some finite radius, r=r_*, depending on different values of the decoupling constant beta . We show that gravitational decoupling via the vanishing complexity factor enhances the stability of the stellar fluid surrounding the core’s central areas. By analyzing the effect of the decoupling constant beta on the M-Y_{TF} plots, (where Y_{TF} denotes the complexity factor) derived from both solutions, we find that a small contribution from the complexity factor leads to the prediction of lower maximum mass of a self-gravitating compact star via gravitational decoupling in f(mathscr {T})-gravity compared to their pure f(mathscr {T})-gravity counterparts. Furthermore, we have also determined the impact of decoupling constant beta and surface density on predicted radii via M{-}R for some known compact objects.

Model for anisotropic compact stars via Chaplygin equation of state in Tolman space-time

In this work, we construct a unique anisotropic solution for spherically symmetric spacetime by investigating the Chaplygin EOS for the anisotropic fluid distribution. For generating the solutions, we have used Tolman metric potential Tolman R C (1939 Phys. Rev., 55, 364–373) to solve the field equations. The anisotropic solution gives well behaved results and the energy conditions are fully satisfied. The TOV equation, Harrison-Zeldovik-Novikov criteria, and adiabatic index have been used to verify the stability of the model. Because this model meets all of these characteristics, it may be used to investigate realistic compact objects. We have also used this model to calculate the masses and radii of compact stars like Her X-1, 4U 1538-52, SAX J1808.4-3658, and LMC X-4, and found that these values were consistent with observational data which was derived using the provided solution.

Relativistic models of anisotropic superdense star in the regime of Karmarkar’s condition

We obtained a new class of solutions for a relativistic anisotropic compact star by utilizing the Karmarkar embedding condition. To obtain the closed-form solution a suitable form of one of the gravitational potentials has been chosen to determine the other by analyzing the Karmarkar condition. The resulting solutions are found to be well-behaved and regular and could describe a compact stellar object. Considering the current estimated values of the mass and radius of the pulsar 4U1820 − 30 as input parameters, all the physically relevant parameters are shown to be well-behaved to a very good degree of accuracy.

Anisotropic compact stars with Karmarkar condition in energy-momentum squared gravity

Anisotropic compact stars with Karmarkar condition in energy-momentum squared gravity

Relativistic polytropic models of charged anisotropic compact objects

In this paper, we introduce new viable solutions to the Einstein-Maxwell field equations by incorporating the features of anisotropic matter distributions within the realm of the general theory of relativity (). To obtain these solutions, we employed the Finch-Skea spacetime, along with a generalized polytropic equation of state (). We constructed various models of generalized polytropes by assuming different values of the polytropic index, i.e., , and . Next, numerous physical characteristics of these considered models were studied via graphical analysis, and they were found to obey all the essential conditions for astrophysical compact objects. Furthermore, such outcomes of charged anisotropic compact star models could be reproduced in various other cases including linear, quadratic, and polytropic

Anisotropic strange compact stars in Krori–Barua spacetime under f(R,G) gravity

There are a number of different theories which tend to explain the concept of universe’s accelerated expansion. Among these theories, modified gravity is the most promising one. This paper elaborates matter distribution along with different characteristics of anisotropic compact stars in [Formula: see text] gravity background. Specifically, to profoundly understand physical behavior of the compact stars, we considered six compact stars, namely: Her X-1 ([Formula: see text]), SAXJ1808.4-3658 ([Formula: see text]), 4U1820-30 ([Formula: see text]), PSR J 1614 2230 ([Formula: see text]), VELA X-1 ([Formula: see text]) and Cen X-3 ([Formula: see text]) and calculated the corresponding quantities such as energy density ([Formula: see text]), radial pressure ([Formula: see text]) and tangential pressure ([Formula: see text]) using three distinct models of [Formula: see text] gravity. For simplicity, [Formula: see text] gravity is divided into two parts as: [Formula: see text]. The first part [Formula: see text] is considered Hu–Sawicki like model, while the second part [Formula: see text] is considered logarithmic like for Model 1 and power law like for Model 2 and Model 3. Predominantly, measurements of anisotropy, the energy conditions (ECs) and stability aspects of models for considered compacts stars are presented using graphical techniques. Furthermore, we also established that for the [Formula: see text] model parameter ([Formula: see text]), all the six stars show conventional behavior.

Anisotropic compact stars with Tolman 𝕍 solution in f(ℛ,𝒯2) gravity

The main purpose of this paper is to study the physical characteristics and stability of anisotropic compact stars in energy–momentum squared gravity. We use Tolman [Formula: see text] solution and consider specific models of this theory to study the viable features of SAX J1808.4-3658, 4U 1538-52 and Her X-1 stars. We explore the behavior of energy density, pressure components, anisotropic factor, energy conditions and equation of state parameter in the interior of considered stars. To check the stability of these stars, we examine the behavior of causality conditions, Herrera cracking approach and adiabatic index. It is found that all the required conditions are satisfied for the proposed models, thus the considered stars are viable as well as stable in this modified theory.

Study of anisotropic compact stars with Krori–Barua spacetime in f(ℛ,𝒯2) gravity

The main objective of this paper is to examine the physical features and stability of anisotropic compact stellar objects in energy–momentum squared gravity. For this purpose, we apply Krori–Barua metric solutions and consider three different models of this modified theory to examine the physical characteristics of Her X-1, 4U 1538-52 and SAX J1808.4-3658 compact stars. We analyze the behavior of various physical quantities such as energy density, pressure components, energy conditions, equation of state parameter and anisotropic factor in the interior of these stars. We then use the estimated values of the sound speed and of the adiabatic index to explore the stability of these compact stars. It is found that all the required conditions are satisfied corresponding to all the selected models. We are therefore allowed to conclude that this modified theory provides viable and stable anisotropic compact stars.

Anisotropic compact stars in presence of electromagnetic field, quintessence field and cosmological constant in f(G) gravity

In this work, we have discussed the anisotropic compact stars in the framework of modified Gauss–Bonnet gravity, named by f(G) theory of gravity. We have found the equations of motion of stars with respect to spherically symmetric metric, describing interior geometry of the compact stellar object, anisotropic mode of the matter distribution in the presence of electromagnetic field and quintessence field. We have taken the metric coefficients in the form [Formula: see text] and [Formula: see text] as well as a particular form of [Formula: see text], where the powers and coefficients of r are constants. The unknown constants are evaluated by matching between interior and exterior Reissner–Nordström–de Sitter metric. We have analyzed some physical aspects like energy density, radial and tangential pressures, anisotropic parameter of matter distribution, energy conditions, mass-radius relation, compactness factor, surface redshift, and stability of our resulting solutions through graphical behavior by comparing to the observational data of different types of compact stars like 4U1820-30, Vela X-1 and SAXJ1808.4-3658. We conclude that all physical attributes maintain their experimental ranges which deliver our anisotropic compact star models are viable and also stable upto certain region in [Formula: see text] gravity theory.

Non-radial oscillations and global stellar properties of anisotropic compact stars using realistic equations of state

In this work, we have made a systematic study of how the gravitational wave frequency of the fundamental mode from compact stars is affected by anisotropic effects using realistic equations of state. Our study is an extension of the seminal research performed by Doneva [Phys Rev D 85:124023, 2012, https://doi.org/10.1103/PhysRevD.85.124023], where a polytropic equation of state was used. To achieve our objective, we considered compact stars which were built by using equations of state in the framework of a relativistic mean field theory for the case of hadronic stars and in the framework of the MIT model for the case of quark stars. In order to obtain some pertinent information that could give us the possibility to detect the anisotropy in compact stars, we also studied and analized the behaviour of various global stellar quantities, e.g., gravitational redshift, stellar mass, radius, among others. We concluded that the anisotropic effects can have important consequences, which are strongly related to the anisotropic parameter and the equation of state of high density matter. Additionally, a comparison with observational data has been made and we have shown that the anisotropic parameter lambda can be used as a tuning parameter to reproduce mass and radius observational data of neutron stars.

Anisotropic compact star with a linear pressure–density relationship

We present a model of compact astrophysical object under General Theory of Relativity using the anisotropic extension of Tolman IV solution. The anisotropy function, derived from the model, remains well behaved throughout the interior of the star. The model satisfies several necessary conditions for a physically realistic compact star. Physical viability of the model is verified specifically by plugging in the estimated parameter values of the Low Mass X-ray Binary (LMXB) candidate 4U 1608–52. Our stability analysis of this star, by using various criteria for stability, provides satisfactory results. In connection to anisotropy, we compute the Tidal Love Number (TLN) for the compact stellar model and compare the calculated values with existing literature.

Gravitational collapse of anisotropic compact stars in modified f(R) gravity

The physically realistic model of compact stars undergoing gravitational collapse in $ f(R) $ gravity has been developed. We consider a more general model $ R + f(R) = R + k R^m $ and describe the interior space-time of gravitationally collapsing stars with separable-form of metric admitting homothetic killing vector. We then investigate the junction conditions to match the interior space-time with exterior space-time. Considering all junction conditions, we find analytical solutions describing interior space-time metric, energy density, pressures, and heat flux density of the compact stars undergoing gravitational collapse. We impose the energy conditions to the model for describing the realistic collapse of physically possible matter distribution for particular models of $GR$, $ R+k R^2 $ and $ R+k R^4 $ gravity. The comprehensive graphical analysis of all energy conditions show that the model is physically acceptable and realistic. We additionally investigate the physical properties of collapsing stars which are useful to decipher the inherent nature of such gravitationally collapsing stars.

Model of hybrid star with baryonic and strange quark matter in Tolman–Kuchowicz spacetime

The purpose of our work is to investigate some new features of a static anisotropic relativistic hybrid compact star composed of strange quark matter (SQM) in the inner core and normal baryonic matter distribution in the crust. Here we apply the simplest form of the phenomenological MIT bag model equation of state [Formula: see text] to correlate the density and pressure of strange quark matter within the stellar interior, whereas radial pressure and matter density due to baryonic matter are connected by the simple linear equation of state [Formula: see text]. In order to obtain the solution of the Einstein field equations, we have used the Tolman–Kuchowicz ansatz [R. C. Tolman, Static solutions of Einstein’s field equations for spheres of fluid, Phys. Rev. 55 (1939) 364–373; B. Kuchowicz, Acta Phys. Pol. 33 (1968) 541] and further derivation of the arbitrary constants from some physical conditions. Here, we examine our proposed model graphically and analytically in detail for physically plausible conditions. In particular, for this investigation, we have reported on the compact object Her [Formula: see text] [[Formula: see text]; [Formula: see text] km] in our paper as a strange quark star candidate. In order to check the physical validity and stability of our suggested model, we have performed various physical tests both analytically and graphically, namely, dynamical equilibrium of applied forces, energy conditions, compactness factor and surface redshift. Finally, we have found that our present model meets all the necessary physical requirements for a realistic model and can be studied for strange quark stars (SQS).

Physical viability of anisotropic compact stars solutions under Karmarkar condition in f(ℛ,𝒯) theory of gravity

In this paper, we investigate the generalized symmetric, static compact objects under anisotropic fluid in the background of Karmarkar embedding class-1 condition. To find the exact solutions of the modified field equations, we consider the gravitational Lagrangian as a linear function of the Ricci scalar and the trace of the stress–energy tensor, i.e. [Formula: see text], where [Formula: see text] is a constant. By employing the concept of Karmarkar condition, we calculate a [Formula: see text] metric component, while for a specific form of [Formula: see text], the gravitational potential is chosen. To attain the closed-form solutions of the modified field equations, we match the interior spacetime metric with the exterior Schwarzschild metric at the boundary and using the numerical values of mass and radius of the compact stars like PSR J1903+327, 4U 1820-30, LMC X-4, and EXO 1785-248, we constraint some unknown parameters. We have discussed physical stability of the stellar configuration by adopting the energy bounds, Tolman–Oppenheimer–Volkov (TOV) equation, adiabatic index, central density and pressure as well. It is concluded that our resulting anisotropic solutions did well behave and a reasonable degree of precision with recent observations.

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

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.

Embedding class 1 model of anisotropic fluid spheres in [formula omitted] gravity

In this article, a completely new model for the spherically symmetric anisotropic compact stars presenting class 1 solutions in the background of f(R,T) gravity, where the functional f(R,T) consider as f(R,T)=R+χT, is presented. All the physical parameters, which are obtained by introducing a compatible grr metric function, are regular and physically well-behaved throughout the interior of star i.e. the reported solutions are physically acceptable to present anisotropic fluid spheres. The solutions satisfy all the energy conditions and causality condition i.e. the representing matter configurations are physical in nature. The satisfaction of TOV-equation and Abreu et al. condition, Γr(r)>4/3, Harrison–Zeldovich–Novikov static condition confirm that the matter configurations represented by our solutions are in equilibrium state and stable, respectively. In our solutions, the coupling parameter χ plays the crucial role, the energy density, pressure and mass are larger for lesser values of χ. The M−R graph generated from our solutions indicates the maximum mass under the observational range. The present model ensures that the f(R,T) gravity is enough suitable to study massive stellar objects in the ground of it. Moreover, all the results of our solutions come back in the Einstein gravity for χ=0.

Behavior of anisotropic fluids with Chaplygin equation of state in Buchdahl spacetime

In the present study we have proposed a new model of an anisotropic compact star which admits the Chaplygin equation of state. For this purpose, we consider Buchdahl ansatz. We obtain the solution of proposed model in closed form which is non-singular, regular and well-behaved. In addition to this, we show that the model satisfies all the energy conditions and maintains the hydrostatic equilibrium equation. This model represents compact stars like PSR B0943+10, Her X-1 and SAX J1808.4-3658 to a very good approximate.