Compact Star Models Research Articles

Model of a charged compact star: A brief study in f(T) gravity

Using modified [Formula: see text] gravity and the diagonal tetrad, we propose a new kind of analytical solution to describe anisotropic charged stellar structures in this study. We obtain precise solutions by applying the linear form of [Formula: see text] as [Formula: see text] in the framework of Tolman–Kuchowicz physically sound metric potentials. The stellar structures of the compact star EXO 1785-248 are then investigated using the model by incorporating a linear equation of state relating the radial pressure [Formula: see text] and the matter density [Formula: see text]. We computed the closed-form expressions for the model parameters and illustrated their characteristics. The comprehensive graphical analysis demonstrates the scientific plausibility, causality, and dynamical stability of the model describing charged anisotropic stars. Finally, using the M-R curve, we estimate the numerical values of mass for different values of [Formula: see text]. The observational data of the neutron star candidates 4U 1820-30, PSR J1614-2230, and PSR J2215 + 5135 are covered by the maximum allowable masses for different values of [Formula: see text] additionally, when [Formula: see text], the charged compact star’s maximum permissible mass is calculated to be [Formula: see text], which could indicate the secondary component of the GW190814 event discovered by LIGO/VIRGO experiments.

Finch–Skea quintessence models in non-conservative theory of gravity

This study is dedicated to presenting a new solution of the field equations in the Rastall theory with a quintessence field defined by the parameter ωq as −1<ωq<−13 by considering the isotropic matter content inside the sphere. The Finch–Skea ansatz (FS) is used in a static and spherically symmetric geometry to obtain the feasible relativistic solution. The results obtained in the physical evaluation are analyzed analytically and graphically. In the appropriate limit of the Rastall coupling parameter, one can regain the original results in the General Relativity. This complete analysis considers five different compact stars: HerX−1 with mass 0.88M⊙ and radius 7.7 km, VelaX−12 with mass 1.77M⊙ and radius 9.99 km, SAXJ1808−3658(SSI) with mass 1.435M⊙ and radius 7.07 km, 4U1608−52 with mass 1.74M⊙ and radius 9.30 km, 4U1538−52 with mass 0.87M⊙ and radius 7.86 km and PSRJ1416−2230 with mass 1.97M⊙ and radius 10.30 km. The physical validity of the obtained solution is verified by computing the necessary physical parameters like energy density and pressure, quintessence density, energy conditions, sound speed via the Herrera cracking concept, hydrostatic equilibrium of forces, mass function, compactness, Buchdahl limit, and surface redshift and analyze their behavior graphically. To investigate the demeanor of these parameters more closely, we computed the numerical values and manifested them in tabular form. We conclude that our presented mathematical model of compact stars in the Finch–Skea geometry with quintessence field fulfills all the requirements for a physically viable solution.

Impact of charge and non-minimal fluid-geometry coupling on anisotropic interiors

This paper explores the interior configuration of various charged anisotropic compact models within the framework of f(R,T,RληTλη) gravity. The chosen model in this theory is represented by R+γRληTλη , where γ is a real-valued parameter. We adopt a static spherical metric to describe the interior of compact strange stars and derive the corresponding field equations. The solution to these equations is then obtained using the Finch-Skea metric and a linear equation of state. Taking the radius and mass of the compact star model 4U 1820-30 as a case study, we investigate the impact of charge and modified corrections on its internal distribution. The stability of the resulting model is also determined within a specific range of γ. Additionally, we determine the values of the model parameter through the vanishing radial pressure constraint, aligning with the experimental data of eight different stars. Our findings indicate that the resulting model adheres to the conditions necessary for physically relevant interiors, particularly in the case of lower charge.

Exploring the physical properties of anisotropic compact objects and constraining their mass–radius relations beyond standard limit in [formula omitted]-gravity

The progress in theoretical modeling of compact high-mass stars in the context of alternative gravity has become important in minimizing challenges associated with neutron star (NS) radius measurements. On this basis, we have presented a rigorous study of compact objects beyond the standard limit in gravity F(Q) in particular F(Q)=b1Q+b2 where b1 and b2 are constants. After formulating the basic equations and finding their relevant solutions by assuming a well-behaved ansatz for the metric potential as well as for anisotropy monitored by the parameters μ1,μ2,b1, along with imposing the boundary conditions on the system under treatment, we have developed a stellar model for anisotropic stars. Specifically, we explored the physical properties of these anisotropic stars and provided novel mass–radius (M−R) relations with models falling in the mass gap of the events GW190814 and GW200210, as well as the effects of slow rotation and moment of inertia on these findings. Interestingly, the behavior of the M−R curves represents a polytropic-type equation of state (EOS) for a negative Λ, while a positive Λ corresponds to a quark matter EOS. However, the analysis reveals that the predicted radii of the compact object observed in the GW190814 event, with a mass of 2.5–2.67 M⊙, is approximately 11.4 km for the de Sitter (dS) case and 11.8 km for the anti-de Sitter (AdS) case, assuming a specific value of the parameter b1=1.1. Furthermore, for b1>1.1, the model predicts the existence of more compact stars with a maximum mass of approximately 3M⊙, which is in good agreement with the R2 model of NSs maintaining the Sly EOS. From the I−M curves, it can be observed that higher values of b1 and μ1 in F(Q) gravity can sustain high moments of inertia (I) of stars with high masses. Interestingly, we obtained the range of I for the dS space as [1.92,3.92]×1045gcm2 and for the AdS space as [2.01,4.03]×1045gcm2 for 1.0≤b1≤1.2.

Insights on the stability of compact stars under Durgapal–Lake metric potentials in the framework of non-conservative theory of gravity

This research deals with the impacts of non-conserved gravitational theory on the physical behavior of three anisotropic compact stars. For this purpose, the metric of static spherically symmetric comprising the anisotropic matter composition is taken into account. To examine the various aspects of some particular compact star models, the Durgapal–Lake metric functions are considered. The unknown parameters involved in Durgapal–Lake metric functions are computed via matching constraints with observed data of masses and radii of three particular stellar objects. The obtained results are noted to be as accurate as possible in terms of physical viability. All the physical crucial parameters and characteristics are displayed graphically and these visuals depict the evaluated solutions that are consistent for three distinct stellar models. It is observed that the parameters occurring in the set of solutions have some valuable insights for these solutions. It is determined that the stars under consideration manifest stable structures corresponding to Durgapal–Lake metric potentials in this framework while they exhibit instability in the case of conservative theory, i.e., general relativity. Further, it is exhibited that for the theory factor equals to zero, the results of general relativity can also be observed graphically.

Compact stars with non-uniform relativistic polytrope

This paper presents new relativistic composite polytropic models for compact stars by simultaneously solving Einstein field equations with the polytropic state equation to simulate the spherically symmetric, static matter distribution. Using a non-uniform polytropic index, we get the Tolman–Oppenheimer–Volkoff equation for the relativistic composite polytrope (CTOV). To analyze the star's structure, we numerically solve the CTOV equation and compute the Emden and mass functions for various relativistic parameters and polytropic indices appropriate for neutron stars. The calculation results show that, as the relativistic parameter approaches zero, we recover the well-known Lane-Emden equation from the Newtonian theory of polytropic stars; thus, testing the computational code by comparing composite Newtonian models to those in the literature yields good agreement. We compute composite relativistic models for the neutron star candidates Cen X-3, SAXJ1808.4-3658, and PSR J1614-22304. We compare the findings with various existing models in the literature. Based on the accepted models for PSR J1614-22304 and Cen X-3, the star's core radius is predicted to be between 50 and 60% percent of its total radius, while we found that the radius of the core of star SAXJ1808.4-3658 is around 30% of the total radius. Our findings show that the neutron star structure may be approximated by a composite relativistic polytrope, resulting in masses and radii that are quite consistent with observation.

Stellar modeling with quintessence field via embedding approach in Ratsall teleparallel gravity

This paper proposes a new model for anisotropic compact stars with quintessence in Rastall teleparallel gravity via embedding approach. In the gravity, the acquired field equations encompassing the anisotropic matter source as well as the quintessence field are studied using the specific character of the scalar torsion [Formula: see text] for the observed stars candidates PSRJ[Formula: see text]1416–2230, 4U[Formula: see text]1608–52, CenX–3, EXO 1785–248 and SMC[Formula: see text]X–1. All of the stellar structures under consideration are said to be advantageously independent of any central singularity and are stable. A thorough graphical analysis reveals that numerous physical properties critical for forming stellar structures are satisfied.

Impact of Tolman–Kuchowicz potentials on Gauss–Bonnet gravity and isotropic stellar structures

In this manuscript, we study the behavior of charged isotropic compact stellar objects within the framework of modified f(G) theory of gravity by considering the Tolman–Kuchowicz spacetime. We use some matching condition of spherically symmetric space–time with Bardeen’s model as an exterior geometry and examine the physical behavior of stellar structures. In the current analysis, we discuss the energy conditions to check the viability of our model. Many physical aspects have been examined, such as energy density, pressure evolution, equation of state parameter, and causality condition. Furthermore, an equilibrium condition can be visualized through the modified Tolman–Oppenheimer–Volkov equation. Further, we study mass–radius function, compactness and redshift function, which are some essential features of charged compact star model. It is worthwhile to mention here for the current study that our stellar structure in the background of Bardeen’s model is more viable and stable.

Charged anisotropic fluid sphere in [formula omitted] gravity satisfying Vaidya - Tikekar metric

In this paper, we study the properties of electrically charged anisotropic and spherically symmetric compact stars in f(Q) gravity theory. The field equations have been solved using the MIT-Bag Equation of State (EoS) along with the Vaidya–Tikekar potential. However, the specific form of charge E2(r)=q0L2r2(1+Lr2)2 has been used to study the charged compact star model. The interior charge anisotropic solution has been matched with the charged Schwarzchild-(Anti)-de-Sitter metric. In particular, this study has been conducted on different compact stars viz, EXO 1785-248, PSR J1614-2230, PSR J0740+620 and SMC X-1. The mass–radius ratio of these compact stars has been predicted, and the physical viability of the model has been checked through the behaviour of causality condition, matter variables, energy constraints, modified TOV equation, and adiabatic index of the star. In conclusion, we observe a well-behaved model of a compact star in f(Q) gravity with charged matter distribution.

Finch–Skea Stellar structures obeying Karmarkar condition in modified [formula omitted] gravity

The current research addresses the composition and modeling of compact dense astrophysical objects in a renowned modified gravity namely f(G) theory, where G denotes the Gauss Bonnet term. In this respect, a family of anisotropic spherically symmetric relativistic solutions of compact objects in hydrostatic equilibrium are obtained. To solve the corresponding modified field equations, we employ the well-famed Karmarkar condition along with the Finch–Skea ansatz for one of the metric potentials. By taking the outer area as Schwarzschild metric, we expand the boundary conditions for spacetime continuity. The unknown constants, appearing in the solutions, are then assessed by using data (mass and radius) of some realistic compact stars namely SMCX-1, 4U 1728-34, 4U 1538-52, EXO 1785-248, SAXJ 1808.4-3658. Furthermore, a graphical analysis is performed for examining the physical behavior of these compact star models. We discuss several physical properties of anisotropic compact stellar structures and explore viability as well as stability of the proposed models. It is concluded that features of established models are in good agreement with the reality of compact stellar structures in the background of f(G) theory.

Non-radial oscillations in newly born compact star considering effects of phase transition

Abstract The massive stars end their lives by supernova explosions leaving central compact objects that may evolve into neutron stars. Initially, after birth, the star remains hot and gradually cools down. We explore the matter and star properties during this initial stage of the compact stars considering the possibility of the appearance of deconfined quark matter in the core of the star. At the initial stage after the supernova explosion, the occurrence of non-radial oscillation in the newly born compact object is highly possible. Non-radial oscillations are an important source of GWs. There is a high chance for GWs from these oscillations, especially the nodeless fundamental (f-) mode to be detected by next-generation GW detectors. We study the evolution in frequencies of non-radial oscillation after birth considering phase transition and predicting the possible signature for different possibilities of theoretical compact star models.

Singularity‐Free Charged Compact Star Model Under F(Q)$F(Q)$‐Gravity Regime

AbstractIn this paper, the possibility of existing a novel class of compact charged spheres based on a charged perfect fluid within the realm of gravity theory is explored. The authors started by proposing physically meaningful explicit formulas for the potential, denoted , and the electric field to find a close‐form solution. More precisely, the change of the dependent variable approach by exploiting the transformation is applied. Successively, the field equations analytically are solved and generate the most general solution, which leads us to examine various significant aspects of the stellar system. These aspects comprise the regularity of gravitational potentials, energy density and pressure, electric charge, the mass‐radius relationship, subluminal sound velocities in the radial direction, and the adiabatic index for charged compact stars. For a more in‐depth system study, mass measurements using contour diagrams are carried out. This mainly involves varying the variable parameters and to distinguish their effect on the mass distribution within the stellar structure. What is more, the electric charge controls the stability of the stellar system is shown, which yields that a stable system can possess a maximum charge of order . The results strongly argue that charged stars could conceivably exist in nature and that such a deviation from traditional theories may be seen in future astrophysical observations.

Study on physical properties and maximum mass limit of Finch–Skea anisotropic model under Karmarkar condition in [formula omitted]-gravity

The primary objective of this work is to study the dynamical characteristics of an anisotropic compact star model with spherical symmetry. This investigation is conducted in the framework of modified f(Q) gravity. To simplify the calculations, we employ the Karmarkar condition and derive a differential equation that establishes a relationship between two crucial components of the spacetime namely eν and eλ. Additionally, we incorporate the well-known Finch–Skea structure as the component representing grr and subsequently find the resulting form of the component gtt from the relation of metric functions to formulate the precise solutions for the stellar structure. To assess the behavior of the anisotropic fluid and stability of the compact star, we use the observed values of mass and radius for the compact star model PSRJ0437−4715. The graphical analysis depicts that the stellar structure possesses physical viability and exhibits intriguing properties. Furthermore, we predicted the mass–radius relation along with the maximum mass limit of several objects for different parameter values by assuming two different surface densities. It is discovered that the compactness rises when density increases.

Impact of [formula omitted] gravity on anisotropic compact star model and stability analysis

The aim of this study is to explore the relativistic anisotropic configuration of a hybrid star in the proximity of strange quark matter and normal baryonic matter within the context of f(Q) theory of gravity. To associate pressure and density due to strange quark matter, the MIT bag model equation of state has been exploited. Here, for establishing the dynamical equations, the Krori–Barua ansatz and a linear form of f(Q) have been considered. We further utilize the Schwarzschild metric as an exterior geometry to find the unknown parameters. Furthermore, several physical properties such as energy density, pressure components, anisotropy, sound speeds, energy conditions, compactness factor, etc., have been analyzed through the graphical representation. Additionally, the variation of bag constant Bg and the measurement of the mass have been examined through contour plots. We further study the mass–radius (M−R) relation to determine the maximum permitted mass. According to our analysis, the maximum mass of a hybrid star rises to more than 2 M⊙ when ‘m’ is decreased. For instance, with m=0.2, the mass of the hybrid star is about 2.6M⊙, which is in the lower mass gap and corresponds to the mass of the lighter component of the GW190814 event. Finally, our investigation validates the stability of the suggested model. We came to the conclusion that f(Q) gravity theory can produce super massive hybrid stars and provide a plausible explanation of the M−R relation that satisfies the observable constraints.

Possible existence of Bose–Einstein condensate compact stars

In this paper, we have model a compact star model composed of Bose–Einstein Condensate (BEC) matter that satisfy a polytropic equation of state (EoS) with γ=2 and a specific density profile. Then we tested the model through various physical criteria like non-singular pressure and density, energy conditions, causality condition etc. Further, we have checked the stability through Bondi criterion, hydrostatic equilibrium and static stability criterion. The stiffness of the EoS, stability, adiabatic index and Mmax depends upon a single parameter k. As k increases, the central Γ decreases near 4/3 and the compactness increases closer to 4/9 while the mass that can hold when increasing central density due to radial perturbation decreases, implies that the system will undergo gravitational collapse sooner if k increases. We have also found that this new category of compact star also follows that constraints provided by GW 170817 event. Hence, this work put forward the possibility of different category of compact star composed of BEC matters that can mimic neutron stars.

Features of anisotropic compact stars in rastall teleparallel gravity via linear equation of state

This paper aims to discuss the model of compact stars based on spherically symmetric spacetime, with a focus on the gravitational effects of Rastall teleparallel gravity, where T represents torsion and λ represents the Rastall parameter. In this study, we evaluate the spherically symmetric spacetime component e a(r) in terms of e b(r) using the linear equation of state p r = β ρ + γ, while the other component e b(r) is assumed from the literature. The paper delves into a detailed analysis of various properties of compact stars such as energy density profile, pressure components, gradients profiles, anisotropic conduct, energy limits, equation of state profiles, velocities of sound profiles, TOV equation profiles, and compactification profile. We use the well-known junction conditions to facilitate the evaluation of the unknown parameters, taking the standard Schwarzschild metric as the outer spacetime. Through detailed analysis in graphical form, we demonstrate that the model showing the anisotropic conduct of stellar objects is viably legitimate, regular, and stable. Overall, the paper provides a comprehensive analysis of the properties of compact stars, which will undoubtedly contribute to our understanding of these astrophysical phenomena.

Isotropization and complexity shift of gravitationally decoupled charged anisotropic sources

This article focuses on investigating the role of decoupling in isotropizing anisotropic, self-gravitational charged sources with spherical symmetry through a well-known gravitational technique, known as minimal geometric deformation (MGD). This technique separates the given system into two gravitational systems: the Einstein-Maxwell system and the gravitational system governed by additional source. We employ novel approaches, including the zero complexity factor and isotropization techniques, to construct various charged compact star models using the Tolman IV as the seed source within the framework of the MGD scheme. The term complexity factor emerges as one of the structure-defining scalar quantities resulting from the orthogonal splitting of the Riemann–Christoffel curvature tensor, as proposed by Herrera (Phys Rev D 97(4):044010, 2018). This scalar function, denoted as YTF\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$Y_{TF}$$\\end{document}, is associated with the fundamental structural characteristics of self-gravitational compact configurations. Our approach is innovative in that it derives the deformation functions by imposing the requirement of YTF=0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$Y_{TF}=0$$\\end{document} and employs isotropization techniques for electrically charged anisotropic configurations.

Some new relativistic charged models with anisotropic pressure

In this paper, we found new classes of solutions to the Einstein-Maxwell field equations with matter anisotropic distribution incorporating a particular form of electric field intensity within the framework of general relativity. We use a metric potential or ansatz that depends on an adjustable parametern in order to get the new solutions. We generated new models of compact stars with n=1 and n=2. Graphical analysis allows us to conclude that the new models satisfy all the physical characteristics for astrophysical objects and can be very useful in the study and description of compact structures. We obtained models consistent with the pulsars PSR J1311-3430 and PSR J0952–0607.

The effect of modified hybrid and logarithmic teleparallel gravity on the interior solutions of compact stars

This study aims to investigate spherically symmetric anisotropic solutions that describe compact stellar objects in the modified Rastall teleparallel (MRT) theory of gravity. In order to achieve this goal, we utilize the Karmarkar condition to evaluate the spherically symmetric components of the line element. We explore the field equations by selecting appropriate off-diagonal tetrad fields for two different scenarios. In the first scenario, we use a hybrid form of f(T)=βemTTn\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$f(T)=\\beta e^{m T} T^n$$\\end{document} and a linear equation of state (EoS) pr=ξρ+ϕ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$p_r=\\xi \\rho +\\phi $$\\end{document}, where 0<ξ<1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$0< \\xi < 1$$\\end{document}, to evaluate h(T). In the second scenario, we again use a hybrid form of f(T)=βemTTn\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$f(T)=\\beta e^{m T} T^n$$\\end{document} and a logarithmic form of h(T)=ψlog(ϕTχ)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$h(T)=\\psi \\log (\\phi T^{\\chi })$$\\end{document}. We aim to investigate the possible forms of gravity modifications by evaluating the function for different values of m and n, reducing the gravity forms to hybrid, power law form, and exponential form. Our findings reveal that the exponential-logarithmic case is unstable in our scenario. To the best of our knowledge, we are the first to attempt to explore compact star models in MRT gravity. After obtaining the field equations, we investigate different physical parameters that demonstrate the stability and physical acceptability of the stellar models. We utilize observational data, such as the mass and radius of the PSRJ1416-2230\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$PSRJ\\;1416-2230$$\\end{document} model, to ensure the physical plausibility of our findings.

Anisotropic strange stars and its maximum mass in Finch-Skea geometry in dimensions D ≥ 4

In this article, we have demonstrated a stellar model for compact stars in the presence of strange matter embedded in D ≥ 4 dimensional space-time defined by the Finch-Skea metric. To study the relevant physical properties of the interior matter, we consider the equation of state (henceforth EOS) as proposed in the MIT bag model, where B is termed the bag constant. The mass-radius relationship in four and higher dimensions is determined using the range of values of surface density through the relation ρ s = 4B, for which bulk strange matter may be a viable issue for compact objects. Here, we choose the range of B so that stable strange matter may exist relative to a neutron at zero external pressure. We note that a maximum value of the stellar radius exists when B is fixed at a given allowed value for which metric functions considered to be real here. This is the maximum allowed radius in this model, which depends on the surface density of a strange star. In four dimensions, the compactness of a star is found to be greater than 0.33. In the case of higher dimensions (D > 4), we observed different values of compactness. Causality conditions are satisfied interior to the star up to the maximum allowed radius , for which the metric function is real. The validity of the energy conditions, surface redshift and other parameters of the stellar configuration are studied, and new results are found. The stability of the model is also studied.