Massive compact Bardeen stars with conformal motion

We consider [Formula: see text] corrected model, i.e. [Formula: see text], where [Formula: see text] is the Ricci scalar and [Formula: see text], [Formula: see text] are arbitrary constant values, to investigate some of the interior configurations of static anisotropic spherical charged stellar structures. The existence of electric charge and a strong electric field confirms due to the higher values of pressure distribution and energy density of the matter inside the stars. Furthermore, for compact star configurations, we also consider the simplified MIT bag model equation of state (EoS) given by [Formula: see text], where [Formula: see text] is radial pressure, [Formula: see text] is energy density and [Formula: see text] is bag constant. This approach allows to find electric charge from the Einstein–Maxwell field equations. We have extensively discussed the behavior of the electric charge and anisotropic fluid distribution factor for five different values of [Formula: see text]. Interestingly, it is noticed during this study, for smaller values of [Formula: see text] we get intensity in electric charge. The Tolman–Oppenheimer–Volkoff equation (TOV), is modified in order to carry electric charge. In particular, we model the compact star candidates SAXJ 1808.4–3658 and Vela X-1 and give graphical representation of some important properties such as equilibrium condition, mass-radius ratio and surface redshift. In the end, our calculated solutions provide strong evidences for more realistic and viable charged stellar model.

We study a new solution for an isotropic compact star model admitting conformal motion in the background of Rastall theory. The conformal Killing vector (\(\mathit{CKV}\)) and the equation of state (EoS) \(p=\omega \rho \), where \(\omega \) satisfying \(0<\omega <1\) is the \(\mathit{EoS}\) parameter for normal matter distribution, are the main ingredients of our methodology. Several physical aspects of the model has been explored analytically to observe the behavior of compact stars such as \(\mathit{TOV}\) equation, energy conditions, Buchdahl condition, stability analysis, compactness and surface redshift. Graphical analysis of the physical parameters have also been presented to support our analytical investigation. We observed that all the physical requirements are fulfilled and the presented model is quite acceptable.

Whether analytic exact vacuum(electrovacuum) solutions of the Einstein(Einstein-Maxwell) field equations can accurately describe or not the exterior spacetime of compact stars remains still an interesting open question in Relativistic Astrophysics. As an attempt to establish their level of accuracy, the radii of the Innermost Stable Circular Orbits (ISCOs) of test particles given by analytic exterior spacetime geometries have been compared with the ones given by numerical solutions for neutron stars (NSs) obeying a realistic equation of state (EoS). It has been so shown that the six-parametric solution of Pach\'on, Rueda, and Sanabria (2006) (hereafter PRS) is more accurate to describe the NS ISCO radii than other analytic models. We propose here an additional test of accuracy for analytic exterior geometries based on the comparison of orbital frequencies of neutral test particles. We compute the Keplerian, frame-dragging, as well as the precession and oscillation frequencies of the radial and vertical motions of neutral test particles for the Kerr and PRS geometries; then we compare them with the numerical values obtained by Morsink and Stella (1999) for realistic NSs. We identify the role of high-order multipole moments such as the mass quadrupole and current octupole in the determination of the orbital frequencies especially in the rapid rotation regime. The results of this work are relevant to cast a separatrix between black hole (BH) and NS signatures as well as probe the nuclear matter EoS and NS parameters from the Quasi-Periodic Oscillations (QPOs) observed in Low Mass X-Ray Binaries.

In this paper, we provide a new parametric class of solutions to Einstein–Maxwell field equations to study the relativistic structure of a compact star via embedding class I condition. The interior of the star is delineated by Karmarkar condition and at the boundary of the star, we match the class of solutions with Bardeen and Reissner–Nordstrom exterior spacetimes. We assume one of the metric potentials as [Formula: see text] to obtain other metric potential. Subsequently, we solve Maxwell field equations. We verify and compare all the thermodynamic properties like matter density, anisotropy, radial and tangential pressures, compactification factor, energy conditions, and stability conditions, namely, adiabatic index, balancing forces via modified TOV equations, Harrision–Zeldovich criteria, casualty condition, Herrera cracking condition, etc., of our class of charged solutions. All the physical and stability conditions are with the viable trend throughout the interior of the stellar object. For a suitable range of values of [Formula: see text] and parameters, it is depicted from this study that the present class of charged solutions yields effective results to obtain realistic and viable modeling of the neutron star in EXO 1785-248 in both the Bardeen and Reissner–Nordstrom exterior spacetimes.

New solution for the Einstein field equations satisfying a neutral anisotropic quark star object is generated. The quark linear equation of state together with the conformal Killing vector (CKV) are used to investigate the behavior and properties of quark stars. The CKV plays an important role in providing the relationship between the two gravitational potentials. The process of combining the CKV and an equation of state has currently led to new realistic solutions. In obtaining the matter variables, one of the gravitational potentials is specified on physical grounds to generate compact star model with physical significance. The generated quark star model undergoes several physical tests for the validity and acceptability. Several realistic physical conditions are found to be satisfied. The model stability in terms of the adiabatic index and equilibrium of the physical forces is satisfied. The behavior of the mass-radius relationship and the surface red shift are well obeyed. Their parameters values are found to be compatible with observations. The gravitational potentials are continuous throughout the interior of the star, and the model's energy conditions are satisfied as well. Quark star models that admit conformal symmetry in the absence of charge are missing in the existing literature.

The present analysis deals with the wormhole (WH) solutions in [Formula: see text] gravity, where [Formula: see text], [Formula: see text] and [Formula: see text] represent the Ricci scalar, kinetic expression and potential field, respectively. To complete this analysis, we use the WH geometry via spherical spacetime with the anisotropic matter distribution. Further, we consider the Gaussian distribution as non-commutative geometry to complete the analysis under conformal symmetry. We calculate the exact WH shape function by plugging the possible conformal Killing vectors. Further, we have discussed the embedded surface to understand the WH geometry. Furthermore, the Tolman–Oppenheimer–Volkoff equation is considered to discuss the stability of WH configuration with the Gaussian energy density source.

In this work, we present a general framework for obtaining exact solutions to the symmetric teleparallel gravity field equations describing strange stars obeying a colour-flavour-locked (CFL) equation of state. This study examines four star candidates: PSR J1614-2230, RXJ1856-37, HER X-1, and SAX J1808-3658. These stars have masses of 1.3 M ⊙ , 0.9031 M ⊙ , 0.98 M ⊙ , and 0.9 M ⊙ , respectively, and radii of 7.259 km, 6 km, 6.7 km, and 7.26 km, respectively. In our study, we solve the f(Q) gravity field equations by assuming a specific metric ansatz g rr component, and evaluate the g tt component by using the colour-flavour-locked (CFL) equation of state. We calculate the exterior spacetime using the principle of f(Q) gravity. The matching of the interior solution with that of the exterior spacetime is employed to determine the model parameters for given realistic compact stars. In this research, we study some properties of stellar models such as the behavior of the density and pressure components, the energy conditions, the metric components, the equation of state components, the sound speeds, the adiabatic index, the gradients, the mass function, the compactness, and the redshift function. Additionally, we examine the stability and equilibrium of the proposed stellar configuration. Our detailed theoretical analysis justifies the realism and feasibility of the stellar configuration considered by demonstrating that the proposed model is free of singularities and satisfies all stability requirements.

Stationary and axisymmetric perfect fluid metrics are studied under the assumption of the existence of a conformal Killing vector field and in the general case of differential rotation. The possible Lie algebras for the conformal group and corresponding canonical line elements are explicitly given. It turns out that only four different cases appear, the Abelian and three others called I, II and III. We explicitly find all the solutions in the Abelian and I cases. For the Abelian case the general solution depends on an arbitrary function of a single variable and the perfect fluid satisfies the equation of state . This class of metrics is the one presented recently by one of us. The general solution for case I is a new Petrov type D metric, with the velocity vector outside the 2-space spanned by the two principal null directions and a barotropic equation of state . For the cases II and III, the general solution has been found only under the further assumption of a natural separation of variables ansatz. The conformal Killing vectors in the solutions that come out here are, in fact, homothetic. No barotropic equation of state exists in these metrics unless for a new Petrov type D solution belonging to case II and with which cannot be interpreted as an axially symmetric solution and such that the velocity vector points in the direction of one of the Killing vectors. This solution has the previously unknown curious property that both commuting Killing vectors are timelike everywhere.

In the present article, we explore a new static, spherically symmetric charged anisotropic fluid model of compact star in curvature coordinates. We consider metric potential g44 of Durgapal’s fifth solution [1] with a specific choice of electric field intensity E and physically acceptable expression of anisotropy factor Δ , which involve parameters K (charge) and Δ (anisotropy) respectively. The solution so obtained is utilized to construct the model for superdense star like neutron star. We have analysed that corresponding to X=0.1, K=2.8, a=1.6 and by assuming surface density , the mass of the compact star comes out to be with radius 14.51 kms, which closely resembles to that of PSRJ0348 + 0432. The solution is well behaved for the values of K satisfying 1≤K5. Our model is described analytically as well as with the help of graphical representations. Our solution is well behaved and free from any central singularity. It also satisfies all the energy conditions as well as the causality condition thus reconfirming the stability of our model.

In this paper, we present a model of a compact relativistic anisotropic star in the presence of an electric field. In order to obtain an exact solution of the Einstein–Maxwell field equations, we assume that the stellar material inside the star obeys a Chaplygin equation of state which is a nonlinear relationship between the radial pressure and the matter density. Using Tolman’s metric potential for [Formula: see text], we obtain the other metric co-efficient by employing the Karmarkar condition which is a necessary and sufficient condition for the interior spacetime of our model to be of embedding class I. Our stellar model is free from central singularity and obeys all the conditions for a realistic stellar object.

We describe a shielding mechanism for a charged black hole immersed in a background involving charged matter fields, solely arising from the Einstein-Maxwell field equations. In particular, we consider a charged generalization of the Einstein cluster, that is a charged black hole surrounded by an effective fluid model for a partially charged dust cloud. We show that the shielding mechanism, arising thereof, is generic and appears in a different parametrization of the problem as well. In this process, we provide the most general electrovacuum solution in a spacetime region devoid of charges, but in the presence of a static and spherically symmetric charge distribution elsewhere. Side by side, we also introduce a convenient parametrization, providing the global solution of the Einstein-Maxwell's field equations in the presence of a charged black hole within the environment of charged fluid. We also comment on the nature of the photon sphere, shadow radius and the eikonal quasi-normal modes in the Einstein-Maxwell cluster.

A new quark star model for a charged anisotropic stellar object is generated using the Einstein–Maxwell field equations. We use a metric function, linear equation of state, and a new measure of anisotropy in form of logarithmic function to formulate the model. For particular choices of parameters in the anisotropic measure, some anisotropic and isotropic models are regained as a special case. Physical analysis indicates that matter variables and gravitational potentials in the model are well behaved. The generated model satisfies the energy, regularity, causality, and stability conditions. The speed of sound is consistent with quark stars.

The aim of this paper is to obtain new physically admissible exact anisotropic stellar models via gravitational decoupling technique. This will be done by taking Korkina and Orlyanskii model solution as a seed solution and extend it to an anisotropic domain via gravitational decoupling through the minimal geometric deformation (MGD) approach. We analyze the physical properties of four compact star models Her [Formula: see text] (Mass [Formula: see text], [Formula: see text][Formula: see text]km), LMC [Formula: see text] ([Formula: see text], [Formula: see text][Formula: see text]km), PSR [Formula: see text] ([Formula: see text], [Formula: see text][Formula: see text]km) and PSR [Formula: see text] ([Formula: see text], [Formula: see text][Formula: see text]km). We demonstrate the stability conditions of the obtained solution by plotting energy conditions, velocity of sound, adiabatic index and all the thermodynamic parameters and equilibrium conditions via TOV equation, etc. We found that the results are physically well behaved and also fulfill the requirement of stability criteria inside the anisotropic fluid sphere. We study the physical features of the solutions in detail, analytically and graphically for the four compact stars Her [Formula: see text], LMC [Formula: see text], PSR [Formula: see text] and PSR [Formula: see text]. Based on the results we realized that the extended gravitational decoupling technique is very effective for the analysis of the interior of the compact stellar structures.

The influence of macroscopic intermediate-range forces (such as the recently postulated ``fifth force'') on stellar structure is investigated through the use of the Lane-Emden equation. It emerges that their effects are similar in magnitude to general-relativistic effects. The Lane-Emden equation is generalized to include intermediate-range forces. To facilitate comparison, the Oppenheimer-Volkoff equation with a polytropic equation of state is cast into Lane-Emden form.

In this work, we have investigated a new solution for charged anisotropic compact stellar system in the framework of an extended theory of symmetric teleparallel gravity known as f(Q, T) gravity with the non-metricity term Q and the trace T for energy–momentum tensor. We have constructed a complete set of the gravitational field equations for a non-linear function f(Q,T)=αQ+β(1+Q2)+λT\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$f(Q,T)=\\alpha Q + \\beta (1+Q^{2}) + \\lambda T$$\\end{document} with α,β\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\alpha , \\beta $$\\end{document} and λ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\lambda $$\\end{document} are dimensionless constant parameters in case of static spherically symmetric space-time. To evaluate the expression of relevant unknown constants interior space-time has been matched with exterior Reissner–Nordstro¨\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\ddot{\ extrm{o}}$$\\end{document}m metric. We have performed a graphical discussion in detail to test the behavior of physical parameters in the interior region of a stellar system like energy density, radial and tangential pressure, anisotropies of matter portion, electric field intensity etc. Also, to check the physical validity of our solutions, we have performed various tests viz., energy conditions, stability, mass–radius relation, surface redshift etc. The hydrostatic equilibrium position of our stellar system has been analysed through the TOV equation. Finally, we have determined that our stellar structure solutions satisfy all required physical conditions for viability and acceptability in the context of some pulsar like neutron stars. So our model can be used to characterise the neutron stars in f(Q, T) modified gravity.