Anisotropic Matter Distribution Research Articles

Study of compact objects: a new analytical stellar model

In this paper, we obtain analytical solutions of Einstein field equations for a spherically symmetric anisotropic matter distributions. For this purpose physically meaningful metric potential corresponds to grr\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$g_{rr}$$\\end{document} and a particular choice of the anisotropy has been utilized to obtain the solutions in closed form. This class of solution has been used to characterized observed pulsars from different aspects. Smooth matching of interior spacetime metric with the exterior Schwarzschild metric and in addition with the condition of vanishing radial pressure across the boundary leads us to determine the model parameters. Pulsar 4U1820-30\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$4U1820-30$$\\end{document} with its current estimated data for mass and radius (Mass =1.58M⊙\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$=1.58 M_\\odot $$\\end{document} and radius =9.1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$=9.1$$\\end{document} km) has been allowed for testing the physical acceptability of our developed model. We have graphically analyzed the gross physical features of the observed pulsar. The stability of the model is also discussed under the conditions of causality, adiabatic index and generalized Tolman–Oppenheimer–Volkov (TOV) equation under the forces acting on the system. Few more pulsars with their have been considered, to show that this model is compatible with observational data, and all the requirements of a realistic star are highlighted. Mass-radius (M–R) relationship have been generated for our model. The impact of anisotropy on the gross physical features of stars have been explored with the graphical presentation.

Some aspects of Morris-Thorne wormhole in gravity

The aim of this manuscript is to study traversable wormhole geometries in the non-metricity and matter coupling gravity. We investigate the Morris-Thorne wormhole metric within the framework of extended symmetric teleparallel gravity. With an anisotropic matter distribution, we explore two distinct wormhole models under two different scenarios. First, we consider the equations of state, and then we assume specific shape functions for each scenario. In both cases, the shape function satisfies all fundamental criteria for a traversable wormhole. We present our results through graphical representations and analyze the energy conditions. Furthermore, we examine the behavior of the wormhole through the anisotropic parameter. Finally, we present our conclusions based on the obtained results.

Towards an understanding of the correlation between the physicochemical and thermal properties of ground rice husks and particle size

The comminution of rice husk has been commonly used to convert it into biogenic silica, bio-oil, biogas, and bioenergy. The composition and structure of biomass are anisotropic, e.g., the surface of the rice husk has a higher silica content than the bulk. It is possible to expect that the physicochemical properties of grinding and sieving rice husks will be distinct due to the difference between the mechanical properties of inorganic and organic matter. A sample of rice husk was ground in a pin mill and sieved. The anisotropic distribution of the inorganic matter was measured on the cross-section of rice husk by SEM-EDX. The chemical composition and textural properties of the rice husk ash were determined by X-ray fluorescence and nitrogen adsorption of each granulometric fraction. Thermochemical, proximate, and ultimate properties of non-calcined grinding rice husks were measured through thermal analysis. Pin, hammer, and knife mills were used to process the rice husks and to determine the effect of the mill type on the comminution operation. Silica is anisotropically distributed in the rice husk but mainly concentrates on the surface. So, The granulometric fractions have very different physicochemical and thermal properties; those with smaller diameters have a higher inorganic matter content; specifically, the pan fraction presents twice the ash content as the non-grinded rice husk. Interestingly, through multivariate analysis, it is possible to classify the fractions into homogeneous groups according to their physicochemical properties for use in technological applications such as pellet fabrication.

Anisotropic Durgapal–Fuloria neutron stars in f(ℛ,T2) gravity

The main purpose of this paper is to obtain physically stable stellar models coupled with anisotropic matter distribution in the context of [Formula: see text] theory. For this, we consider a static spherical geometry and formulate modified field equations containing various unknowns such as matter determinants and metric potentials. We then obtain a unique solution to these equations by employing Durgapal–Fuloria ansatz possessing a constant doublet. We also use matching criteria to calculate the values of these constants by considering the Schwarzschild exterior spacetime. Two different viable models of this modified theory are adopted to analyze the behavior of effective matter variables, anisotropy, energy conditions, compactness and redshift in the interiors of Her X-1, PSR J0348-0432, LMC X-4, SMC X-1, Cen X-3, and SAX J 1808.4-3658 star candidates. We also check the stability of these models by using three different physical tests. It is concluded that our considered stars satisfy all the physical requirements and are stable in this modified gravity for the considered parametric values.

Charged Spherical Solution in Torsion and Matter Coupling Gravity and Influence of Torsion Parameter and Electric Charge on Compact Stars in Lower Mass Gap

Abstract In this study, we explore a new exact solution for a charged spherical model as well as the astrophysical implications of the torsion parameter χ1 and electric charge Q on compact stars in lower mass gaps in the $f(\mathcal {T})$ gravity framework. Commencing with the field equations that describe anisotropic matter distributions, we select a well-behaved ansatz for the radial component of the metric function, along with an appropriate formulation for the electric field. The resulting model undergoes rigorous testing to ensure its qualification as a physically viable compact object within the $f(\mathcal {T})$ gravity background. We extensively investigate two factors: χ1 and Q, carefully analyzing their impacts on the mass, radius, and stability of the star. Our analyses demonstrate that our models exhibit well-behaved behavior, free from singularities, and can successfully explain the existence of a wide range of observed compact objects. These objects have masses ranging from $0.85^{+0.15}_{-0.15}$ to 2.67 M⊙, with the upper value falling within the mass gap regime observed in gravitational events like GW190814. A notable finding of this study has two aspects: we observe significant effects on the maximum mass (Mmax) and the corresponding radii of these objects. Increasing values of χ1 lead to higher Mmax (approximately $2.64^{+0.13}_{-0.14}$) and smaller radii (approximately $10.40^{+0.16}_{-0.60}$), suggesting the possibility of the existence of massive neutron stars within the system. Conversely, increasing values of Q result in a decrease in Mmax (approximately $1.70^{+0.05}_{-0.03}$) and larger radii (approximately $13.71^{+0.19}_{-0.20}$). Furthermore, an intriguing observation arises from comparing the results: for all values of χ1, nonrotating stars possess higher masses compared to slow-rotating stars, whereas this trend is reversed when adjusting Q.

Exploring the applicability of traversable wormhole formation in [formula omitted] gravity

In this work, we construct three different models of static wormhole (WH) geometries within the realm of f(R,Lm) gravity theory. We start by deriving the corresponding field equations for the Morris–Thorne WH geometry in the context of anisotropic matter distribution under the generic form of f(R,Lm) gravity. By adequately specifying the key features of three different shape function models generated with different assumptions about their matter content, and assuming that WHs exert no tidal force by setting the gravitational redshift function to be a constant or φ′(r)=0, we disclose a variety of exact WH solutions in the theory. Our exact solutions for f(R,Lm) show that for all three classes of WHs found, the energy density is consistently positive in all spacetime, while the radial pressure is negative. This signifies that exotic matter is mandatory for the existence of WHs in f(R,Lm) gravity. We have also applied the energy conditions (ECs) for the WHs’ physical content and found that exact WH models are filled with exotic matter that violates the necessary ECs throughout spacetime and makes them compatible and traversable.

Gravitationally decoupled charged anisotropic solutions in Rastall gravity

This paper develops the stellar interior geometry for charged anisotropic spherical matter distribution by developing an exact solution of the field equations of Rastall gravity using the notion of gravitational decoupling. The main purpose of this investigation is the extension of the well-known isotropic model within the context of charged isotropic Rastall gravity solutions. The second aim of this work is to apply gravitational decoupling via a minimal geometric deformation scheme in Rastall gravity. Finally, the third one is to derive an anisotropic version of the charged isotropic model previously obtained by applying gravitational decoupling technology. We construct the field equations which are divided into two sets by employing the geometric deformation in radial metric function. The first set corresponds to the seed (charged isotropic) source, while the other one relates the deformation function with an extra source. We choose a known isotropic solution for spherical matter configuration including electromagnetic effects and extend it to an anisotropic model by finding the solution of the field equations associated with a new source. We construct two anisotropic models by adopting some physical constraints on the additional source. To evaluate the unknown constants, we use the matching of interior and exterior spacetimes. We investigate the physical feasibility of the constructed charged anisotropic solutions by the graphical analysis of the metric functions, density, pressure, anisotropy parameter, energy conditions, stability criterion, mass function, compactness, and redshift parameters. For the considered choice of parameters, it is concluded that the developed solutions are physically acceptable as all the physical aspects are well-behaved.

Anisotropic quintessence compact star in f(T) gravity with Tolman–Kuchowicz metric potentials

To obtain analytically relativistic quintessence anisotropic spherical solutions in the f(T) paradigm is the primary objective of this paper. To do this, the pressure anisotropy condition is imposed, and we employ a metric potential of the Tolman–Kuchowicz (TK) type. We also suppose that our current model incorporates a quintessence field characterized by a parameter ω q , in addition to the anisotropic matter distribution. In the presence of the parameter α, the field equations are modified by the choice of the f(T) function. The f(T) gravity parameter α adds new components to the basic physical characteristics, such as density, pressure, subliminal sound velocity, surface redshift, etc, of the present model. By selecting the compact star Her X-1 and varying α from 0.5 to 2.5, we examined all the physical characteristics of the model parameter of the configuration. The graphical process demonstrates that a more compact item is produced with greater values of α. The hydrostatic equilibrium condition of the model is discussed, as well as the mass-radius relationship for our current model is obtained.

Anisotropic dark matter distribution in Saez–Ballester theory of gravitation

Anisotropic dark matter distribution in Saez–Ballester theory of gravitation

Anisotropic quark stars in energy-momentum squared gravity

At super-saturation densities, quarks in the core of neutron stars (NSs) have been a subject of intense investigation for last few decades. In particular, an intriguing conjecture has emerged suggesting that the true ground state of hadronic matter may be strange quark matter (SQM). In the present manuscript, we study internal structure and the physical properties of quark stars (QSs) in energy-momentum squared gravity (EMSG) with MIT bag model equations of state (EoS). An important feature of this theory is the addition of the term f(TμνTμν) to the Einstein-Hilbert action. This modification in the action lead to changes in the right-hand side of Einstein's field equations (EFE). We obtain mass-radius relations for a spherically symmetric configuration supported by the anisotropic fluid matter distribution and solved the hydrostatic equilibrium equations numerically in the framework of EMSG. In addition, we present and discuss the stability of stellar structure depending on the model parameters.

Relativistic tolman stellar spheres in f(R,ϕ) theory of gravity

In this study, we investigate the literature on anisotropic stellar spheres in [Formula: see text] gravity utilizing Tolman–Kuchowicz (TK) spacetime. Due to the existence of anisotropic matter distribution, we derive the equations of motion for spherically symmetric spacetime by taking into account physically accurate formulations of the metric potentials. For this purpose, we develop the matching conditions by comparing them with the exterior solution to determine the TK constants. We have also discussed the graphical analysis of energy density, pressure components, equation of state components, equilibrium condition, and stability analysis. Moreover, other properties of a compact star, like the mass–radius function, compactness, and redshift function, have also been investigated. It is also noticed that energy conditions are satisfied, which justifies that our considered stars are viable. The validity of our proposed model has been proven by studying the development of various physical characteristics, and it is determined that our system is physically stable and free of any singularities.

Physical properties of a quintessence anisotropic stellar model in f(Q) gravity and the mass–radius relation

In this article, we present a new family of solutions to the Einstein field equations of an uncharged spherically symmetric anisotropic matter distribution in the context of f(Q) gravity by choosing f(Q)=Q+aQ^2, a being the coupling constant. Along with the fundamental quintessence dark energy defined by the equation of state parameter -1<omega _q<-frac{1}{3}, we have generated the field equations in modified gravity. Using the linear relationship between radial pressure and energy density along with the Krori–Barua (KB) metric potential, we are able to solve the field equations. Next, we discuss the smooth matching between the exterior Schwarzschild spacetime and the interior spherically symmetric spacetime. We have presented a thorough physical analysis of several factors analytically and graphically to show the physical viability of our suggested model. For the compact star SAXJ 1808.4-3658, our entire graphical analysis was carried out in the context of our solutions for various values of the coupling constant connection to the f(Q) gravity. The influence of coupling constant “a” on different model parameters has been numerically determined and is presented in tabular form. We checked the radial and tangential sound speeds, the stability factor, the adiabatic index, etc. to determine whether our model was stable. It is evident from our analysis that the model is potentially stable when coupling constant a in [0,,5]. The maximum allowable mass and radius from our present model have been obtained through the mass–radius (M-R) plot for different values of a.

Effects of f(R, G) gravity on anisotropic charged compact objects

The present study provides an in-depth analysis of the anisotropic matter distribution and various physical aspects of compact stars in the context of a f(R, G)-gravity framework. In order to gain an exhaustive understanding of these aspects, our study focuses on three particular compact stars: VELA X-1 (CS1), SAXJ1808.4-3658 (CS2), and 4U1820-30 (CS3). We conducted calculations on the relevant characteristics of these compact stars by employing three different models of f(R, G)-gravity. As a convenient approach, the f(R, G)-gravity is organized into two distinct components, which include f 1(R) and f 2(G). The R dependent component is modeled similarly to the Hu-Sawicki approach, while for modeling the G dependent component, we chose logarithmic and power law-like approaches and suggested three viable gravity models. Graphical methods are used to analyze the physical properties of the compact stars in the domain of suggested models of gravity.

Static traversable wormhole solutions in f(R,ℒm) gravity

In this study, we explore the new wormhole solutions in the framework of new modified $f(R,L_m)$ gravity. To obtain a characteristic wormhole solution, we use anisotropic matter distribution and a specific form of energy density. As second adopt the isotropic case with a linear EoS relation as a general technique for the system and discuss several physical attributes of the system under the wormhole geometry. Detailed analytical and graphical discussion about the matter contents via energy conditions is discussed. In both cases, the shape function of wormhole geometry satisfies the required conditions. Several interesting points have evolved from the entire investigation along with the features of the exotic matter within the wormhole geometry. Finally, we have concluding remarks.

Relativistic configurations of Tolman stellar spheres in f(𝒢,𝒯 ) gravity

This study is devoted to investigate the formation of compact stars using Tolman–Kuchowicz space-time in [Formula: see text] gravity. By taking into account the physically reliable formulations of metric potentials, [Formula: see text] = [Formula: see text] and [Formula: see text] = [Formula: see text], we investigate the equation of motion for spherically symmetric space-time in the presence of an anisotropic matter distribution. Furthermore, matching conditions are employed to compute the unknown constants. By making use of dynamical equations, the pivotal relevant aspects, including energy density, radial and tangential pressures, dynamical equilibrium, anisotropy effect, energy conditions and stability, are physically tested in order to determine the physical acceptability of yielding celestial model, which are thoroughly compared with experimental facts and figures of ten different compact stars. Finally, we observe that obtained anisotropic outcomes are physically viable, free from geometrical and physical singularities. Moreover, these outcomes also provide circumstantial evidence for the existence of super-massive compact stars.

Wormhole geometry and three-dimensional embedding in extended symmetric teleparallel gravity

In the present manuscript, we study traversable wormhole solutions in the background of extended symmetric teleparallel gravity with matter coupling. With the anisotropic matter distribution we probe the wormhole geometry for two different gravity models. Primarily, we consider the linear model f(Q,T)=Q+2ξT. Firstly, we presume a logarithmic form of shape function and analyze the scenario for different redshift functions. Secondly, for a specific form of energy density, we derive a shape function and note its satisfying behavior. Next, for the non-linear model f(Q,T)=Q+αQ2+βT and a specific shape function we examine the wormhole solution. Further, with the aid of embedding diagrams, we interpreted the geometry of wormhole models. Finally, we conclude results.

Study of charged cylindrical collapse in [formula omitted] gravity

This paper investigates the effects of electromagnetic field on the gravitational collapse in f(R,T,Q) theory, where Q=RφϑTφϑ. For this, we assume dynamical cylindrically symmetric self-gravitating geometry which is coupled with generalized anisotropic matter distribution as well as dissipation flux. We adopt the model R+ΦT+ΨQ to formulate the corresponding dynamical and transport equations by employing the Misner–Sharp as well as Müler-Israel Stewart formalisms, where Φ and Ψ are real-valued coupling constants. The influence of state variables, heat dissipation, charge and the bulk viscosity on the collapsing phenomenon is then studied by establishing some relations between these evolution equations. Moreover, the Weyl scalar and the modified field equations are expressed in terms of each other. We apply some constraints on the considered modified model and the fluid configuration to obtain conformally flat spacetime. Finally, we address different cases to check how the modified corrections and charge affect the collapse rate of cylindrical matter source.

Geometric structures of Morris-Thorne wormhole metric in f(, ℒ m ) gravity and energy conditions

The aim of this manuscript is to study the traversable wormhole (WH) geometries in the curvature matter coupling gravity. We investigate static spherically symmetric Morris-Thorne WHs within the context of gravity. To accomplish this, we examine the WH model in four different cases (i) linear model, with anisotropic matter distribution having the relation p r = mp t (ii) linear model having anisotropic matter distribution along with the equation of state parameter, p r = ω ρ, (iii) non-linear model with specific form of energy density and (iv) non-linear model, with isotropic matter distribution and having the linear relation between pressure and energy density, p = ω ρ. Additionally, in the latter case, we consider a specific power-law shape function . Furthermore, we analyze the energy conditions for each WH model to verify their physical viability. As a novel outcome, we can see the validation of the null energy condition for the model that suggests ruling out the necessity of exotic matter for the traversability of the WH. At last, an embedding diagram for each model is illustrated that describes the WH geometry.

New wormhole solutions using dark matter profiles with the signature of observational data in teleparallel gravity

In this paper, we calculate a new class of wormhole solutions in the framework of teleparallel gravity. To obtain a characteristic wormhole solution, we use anisotropic matter distribution and a specific form of two dark matter profiles (URC profile and Quantum wave dark matter). As a general strategy, we create a relationship between calculated energy density and dark matter profiles for the system and investigate the physical properties of the wormhole geometry. A detailed analytical and graphical explanation of the matter contents via energy conditions is provided. The calculated shape functions of wormhole geometry meet the required conditions in both circumstances. Several intriguing features have emerged from the investigation, as have the properties of the exotic matter within the wormhole geometry. Finally, we have concluding remarks.

Study of compact stars in {mathcal {R}}+ alpha {mathcal {A}} gravity

The main goal of this work is to provide a comprehensive study of relativistic structures in the context of recently proposed {mathcal {R}}+ alpha {mathcal {A}} gravity, where {mathcal {R}} is the Ricci scalar, and {mathcal {A}} is the anti-curvature scalar. For this purpose, we examine a new classification of embedded class-I solutions of compact stars. To accomplish this goal, we consider an anisotropic matter distribution for {mathcal {R}}+ alpha {mathcal {A}} gravity model with static spherically symmetric spacetime distribution. Due to highly non-linear nature of field equations, we use the Karmarkar condition to link the g_{rr} and g_{tt} components of the metric. Further, we compute the values of constant parameters using the observational data of different compact stars. It is worthy to mention here that we choose a set of twelve important compact stars from the recent literature namely 4U~1538{-}52, SAX~J1808.4{-}3658, Her~X{-}1, LMC~X{-}4, SMC~X{-}4, 4U~1820{-}30, Cen~X{-}3, 4U~1608{-}52, PSR~J1903{+}327, PSR~J1614{-}2230, Vela~X{-}1, EXO~1785{-}248. To evaluate the feasibility of {mathcal {R}}+ alpha {mathcal {A}} gravity model, we conduct several physical checks, such as evolution of energy density and pressure components, stability and equilibrium conditions, energy bounds, behavior of mass function and adiabatic index. It is concluded that {mathcal {R}}+ alpha {mathcal {A}} gravity supports the existence of compact objects which follow observable patterns.