arXiv subjects

Pramit Rej

Publications and source records attributed to Pramit Rej.

At least 19 recordsLinked to original sources

arXiv2026

Implications of Adler-Finch-Skea solution on charged dark energy star satisfying Karmarkar Condition

A possible approach for preventing compact astrophysical objects from gravitational collapse into singularities is the idea of dark energy. Since it is the cause of our universe's accelerated expansion, it has the greatest impact on the cosmos. As a result, it appears that dark energy can interact with any compact astrophysical stellar object [Phys. Rev. D 103, 084042 (2021)]. In this study, our primary objective is to develop a simpler model of a charged strange star coupled with anisotropic dark energy admitting the Adler-Finch-Skea solution [J. Math. Phys. 15, 727 (1974); Class. Quantum Grav. 6, 467 (1989)] within Einstein gravity. To develop this model, the Karmarkar condition was employed to determine the radial metric component, while Adler's methodology was used to choose the time-metric component. For this purpose, we explored a particular strange star, Her X-1, with observed values of mass $(0.85 \pm 0.15)M_{\odot}$ and radius $= 8.1_{-0.41}^{+0.41}$ km. In this context, we proceeded to model dark energy using the equation of state (EoS), such that the density of dark energy is proportional to the density of isotropic perfect fluid matter. The unknown constants in the metric were determined by smooth matching using the Darmois-Israel criterion. We conduct an in-depth examination of the stability and force equilibrium of our suggested star framework, as well as several physical characteristics of the model such as the metric function, pressure, density, mass-radius relation, and dark energy parameters. Thus, the physical consistency and stability of the present model are investigated. Therefore, following a comprehensive theoretical investigation, we discovered that our proposed model is singularity free and meets all the stability requirements to be a stable and physically realistic stellar model.

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arXiv2024

Well behaved class of Heintzmann's solution within $f(R,\,T)$ framework

The primary objective of this paper is to develop a well-behaved class of Heintzmann IIa [{\em H. Heintzmann, Z. Physik 228, 489-493 (1969)}] solution in the context of $f(R,\, T)$ gravity. In the $f(R, T)$ framework, the gravitational action includes both the Ricci scalar ($R$) and the trace of the energy-momentum tensor ($T$). We chose a particular $f(R,\,T)$ model s.t. $f(R,\,T) = R+2 \chi T$, where $\chi$ is known as the coupling parameter. This solution describes a novel isotropic compact fluid sphere with positively finite central pressure and density in this extended theory of gravity. The results obtained analytically are better described by graphical representations of the physical parameters for various values of the coupling parameter $\chi$. The solution for a specific compact object, Vela X-1, with radius $\mathfrak{R} = 9.56_{-0.08}^{+0.08}$ km and mass $\mathcal{M} = 1.77 \pm 0.08~\mathcal{M}_{\odot}$ [{\em M. L. Rawls et al. ApJ, 730, 25 (2011)}], is shown here. We analyze the fundamental physical attributes of the star, which reveals the influence of the coupling parameter $\chi$ on the values of substance parameters. This helps us to make a fruitful comparison of this modified $f(R,\, T)$ gravity with the standard GR and notice that it holds good for stable compact objects. In this framework, the star under our consideration exhibits a stable structure consistent with the Heintzmann IIa {\em ansatz}. From all of our obtained graphical and numerical results, we can ultimately conclude that our reported model is physically admissible and satisfies all the physical criteria for an acceptable model.

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arXiv2024

Charged analog of anisotropic dark energy star in Rastall gravity

Dark energy is one of the potential strategies for preventing compact objects from gravitationally collapsing into singularities. Because it is the cause of the accelerated expansion of our universe, it has the greatest impact on the cosmos. Thus, it is plausible that dark energy will interact with any stellar object that is compact in the universe [\textit{Phys. Rev. D} \textbf{103}, 084042 (2021)]. Our main goal in this work is to create a simplified model, in the Rastall gravitational framework, of a charged strange star coupled to anisotropic dark energy in Krori-Barua spacetime [\textit{J. Phys. A, Math. Gen.} \textbf{8}:508, 1975]. Here, we consider a specific strange star object, Her X-1, with observed values of mass $=(0.85 \pm 0.15)M_{\odot}$ and radius $= 8.1_{-0.41}^{+0.41}$ km., so that we can develop our model. In this context, we began by modeling dark energy using the equation of state (EoS), in which the dark energy density is proportional to the isotropic perfect fluid matter-energy density. The Darmois-Israel condition has been used to calculate the unknown constants that are present in the metric. We perform a detailed analysis of the model's physical properties, including the mass-radius relation, pressure, density, metric function, and dark energy parameters, by varying the Rastall coupling parameter. We also examine the stability and force equilibrium of our proposed stellar configuration. Following a comprehensive theoretical analysis, we discovered that our suggested model is both singularity-free and meets all stability requirements needed to be a stable, physically reasonable stellar model.

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arXiv2024

Hybrid star within $f(\mathcal{G})$ gravity

The purpose of this work is to investigate some interesting features of a static anisotropic relativistic stellar object composed of two different types of fluid distributions typically termed as quark matter (QM) and ordinary baryonic matter (OBM) together with Krori-Barua type (KB) {\em ansatz} in the regime of modified $f(\mathcal{G})$ gravity, where $\mathcal{G}$ being the Gauss-Bonnet invariant term. In order to explain the correlation between pressure and matter density for the quark matter distribution within the compact object, we have taken into consideration the well-known MIT bag equation of state (EoS) whereas there is a simple linear correlation between pressure and matter density for ordinary baryonic matter. Furthermore, using graphical representations for varying parameters, the physical credibility of our obtained solutions has been intensively examined by regularity checking of the metric coefficients and matter variables, energy conditions, mass function, and causality conditions. For these analyses, we consider a particular compact stellar candidate 4U 1538-52. Finally, we found that the resulting outcome depicts the viability of the considered hybrid stellar model.

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arXiv2024

Polytropic stellar structure in 5$\mathcal{D}$ Einstein-Gauss-Bonnet gravity

Polytropic stars are useful tools for learning about stellar structure without the complexity of comprehensive stellar models. These models rely on a certain power-law correlation between the star's pressure and density. This paper proposes a polytropic star model to investigate some new features in the context of $5\mathcal{D}$ Einstein-Gauss-Bonnet (EGB) gravity using the Finch-Skea {\em ansatz} [{\em M. R. Finch and J. E. Skea, Classical and Quantum Gravity 6, 467 (1989)}]. Analytical results are better described by graphical representations of the physical parameters for various values of the Gauss-Bonnet coupling constant $\alpha$. The solution for a specific compact object, EXO 1785-248, with radius $\mathfrak{R} = 8.849_{-0.04}^{+0.04}$ km and mass $\mathcal{M} = 1.3 \pm 0.02~\mathcal{M}_{\odot}$, is shown here. We analyze the essential physical attributes of the star, which reveal the influence of the coupling parameter $\alpha$ on the values of the parameters. Ultimately, we conclude that our current model is realistic because it satisfies all the physical criteria for an acceptable model.

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arXiv2023

Celestial attributes of Hybrid star in $5\mathcal{D}$ Einstein-Gauss-Bonnet gravity

Hybrid star is the term given to a neutron star with a quark core. Due to a lot of uncertainties in the calculations and compositions of such a high-density system, it is of great interest and a preferred scenario for particle physicists and astrophysicists. To explore some novel aspects within the framework of the $5\mathcal{D}$ Einstein-Gauss-Bonnet(EGB) gravity, our current study presents a hybrid star model that includes strange quark matter in addition to regular baryonic matter. In hybrid stellar objects, a hadronic outer component surrounds a quark inner component, which prompts the consideration of the most basic MIT bag model equation of state to correlate the density and pressure of strange quark matter within the stellar interior, while radial pressure and matter density due to baryonic matter are connected by a linear equation of state. The model is constructed within the specifications of the Krori and Barua (KB) {\em ansatz} (Krori and Barua, J. Phys. A: Math. Gen. $\bold{8},508, 1975$). Here we present the solution for a particular compact object 4U 1538 - 52 with mass $\mathcal{M} = 0.87 \pm 0.07~\mathcal{M}_{\odot}$ and radius $\mathfrak{R} = 7.866_{-0.21}^{+0.21}$ km. We examine the fundamental physical characteristics of the star, which highlights how the values of matter variables are affected by the Gauss-Bonnet coupling parameter $\alpha$. Finally, as it meets all the physical requirements for a realistic model, we have come to realize that our present model is realistic.

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arXiv2023

Relativistic isotropic stellar model in $f(R,\,T)$ gravity with Durgapal- IV Metric

In this work, a new static, non-singular, spherically symmetric fluid model has been obtained in the background of $f(R,\,T)$ gravity. Here we consider the isotropic metric potentials of Durgapal-IV [M.C. Durgapal, J. Phys. A {\bf 15} 2637 (1982)] solution as input to handle the Einstein field equations in $f(R,\,T)$ environment. For different coupling parameter values of $\chi$, graphical representations of the physical parameters have been demonstrated to describe the analytical results more clearly. It should be highlighted that the results of General Relativity (GR) are given by $\chi=0$. With the use of both analytical discussion and graphical illustrations, a thorough comparison of our results with the GR outcomes is also covered. The numerical values of the various physical attributes have been given for various coupling parameter $\chi$ values in order to discuss the impact of this parameter. Here we apply our solution by considering the compact star candidate LMC X-4 [M.L. Rawls et al., Astrophys. J. {\bf 730} 25 (2011)] with mass$=(1.04 \pm 0.09)M_{\odot}$ and radius $= 8.301_{-0.2}^{+0.2}$ km. respectively, to analyze both analytically and graphically. To confirm the physical acceptance of our model, we discuss certain physical properties of our obtained solution such as energy conditions, causality, hydrostatic equilibrium through a modified Tolman-Oppenheimer-Volkoff (TOV) conservation equation, pressure-density ratio, etc. Also, our solution is well-behaved and free from any singularity at the center. From our present study, it is observed that all of our obtained results fall within the physically admissible regime, indicating the viability of our model.

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arXiv2023

Charged strange star coupled to anisotropic dark energy in Tolman-Kuchowicz spacetime

The concept of dark energy can be used as a possible option to prevent the gravitational collapse of compact objects into singularities. It affects the universe on the largest scale, as it is responsible for our universe's accelerated expansion. As a consequence, it seems possible that dark energy will interact with any compact astrophysical stellar object [Phys. Rev. D 103, 084042 (2021)]. In this work, our prime focus is to develop a simplified model of a charged strange star coupled to anisotropic dark energy in Tolman-Kuchowicz spacetime (Tolman, Phys Rev 55:364, 1939; Kuchowicz, Acta Phys Pol 33:541, 1968) within the context of general relativity. To develop our model, here we consider a particular strange star object, Her X-1 with observed values of mass $=(0.85 \pm 0.15)M_{\odot}$ and radius $= 8.1_{-0.41}^{+0.41}$ km. respectively. In this context, we initially started with the equation of state (EoS) to model the dark energy, in which the dark energy density is proportional to the isotropic perfect fluid matter-energy density. The unknown constants present in the metric have been calculated by using the Darmois-Israel condition. We perform an in-depth analysis of the stability and force equilibrium of our proposed stellar configuration as well as multiple physical attributes of the model such as metric function, pressure, density, mass-radius relation, and dark energy parameters by varying dark energy coupling parameter $\alpha$. Thus after a thorough theoretical analysis, we found that our proposed model is free from any singularity and also satisfies all stability criteria to be a stable and physically realistic stellar model.

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arXiv2023

Charged strange star model in Tolman-Kuchowicz spacetime in the background of 5D Einstein-Maxwell-Gauss-Bonnet gravity

In this article, we provide a new model of static charged anisotropic fluid sphere made of a charged perfect fluid in the context of 5D Einstein-Maxwell-Gauss-Bonnet (EMGB) gravity theory. To generate exact solutions of the EMGB field equations, we utilize the well-behaved Tolman-Kuchowicz (TK) {\it ansatz} together with a linear equation of state (EoS) of the form $p_r=\beta \rho-\gamma$, (where $\beta$ and $\gamma$ are constants). Here the exterior space-time is described by the EGB Schwarzschild metric. The Gauss-Bonnet Lagrangian term $\mathcal{L}_{GB}$ is coupled with the Einstein-Hilbert action through the coupling constant $\alpha$. When $\alpha \to 0$, we obtain the general relativity (GR) results. Here we present the solution for the compact star candidate EXO 1785-248 with mass$=(1.3 \pm 0.2)M_{\odot}$; Radius $= 10_{-1}^{+1}$ km. respectively. We analyze the effect of this coupling constant $\alpha$ on the principal characteristics of our model, such as energy density, pressure components, anisotropy factor, sound speed etc. We compare these results with corresponding GR results. Moreover, we studied the hydrostatic equilibrium of the stellar system by using a modified Tolman-Oppenheimer-Volkoff (TOV) equation and the dynamical stability through the critical value of the radial adiabatic index.The mass-radius relationship is also established to determine the compactness factor and surface redshift of our model. In this way, the stellar model obtained here is found to satisfy the elementary physical requirements necessary for a physically viable stellar object.

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arXiv2022

Isotropic Buchdahl's relativistic fluid sphere within $f(R,\,T)$ gravity

The aim of the research is to look into a new solution for isotropic compact stars in the context of the $f(R,\,T)$ theory of gravity. We used the Buchdahl [H.A. Buchdahl, Phys. Rev. {\bf 116} (1959) 1027] metric potentials as input to deal with the field equations in the $f(R,\,T)$ framework. For different values of the coupling parameter $\chi$, graphical representation of the model parameters have been shown to canvass the analytical results more clearly. Interestingly, we have proven that for $\chi=0$, the standard General Relativity (GR) results can be recovered. A comparison of our obtained solutions with the GR results is also discussed. To study the effect of the coupling parameter $\chi$, the numerical values of the different physical variables have been tabulated for the values of the coupling parameter $\chi=0,\,0.25,\,0.5,\,0.75,1,\,1.25$. We used the compact stars candidate LMC X-4 with mass$=(1.04 \pm 0.09)M_{\odot}$; Radius $= 8.301_{-0.2}^{+0.2}$ km. respectively, for graphical analysis. To determine the physical acceptability of the model, we looked into the necessary physical properties such as energy conditions, causality, hydrostatic equilibrium, and pressure-density ratio etc. and found that our system satisfies all of these criteria, indicating that the model is physically reasonable.

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arXiv2022

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

The purpose of our present 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 $p_q = \frac{1}{3}(\rho_q - 4B_g)$ 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 $p_r = \alpha \rho - \beta$. In order to obtain the solution of the Einstein field equations, we have used the Tolman-Kuchowicz {\em ansatz} [Tolman, Phys Rev 55:364, 1939; Kuchowicz, Acta Phys Pol 33:541, 1968] 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 $X-1$ [Mass=$(0.98 \pm 0.12)M_{\odot}$; Radius= $8.1_{-0.41}^{+0.41}$ 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 etc. 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).

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arXiv2021

Tolman IV fluid sphere in f(R, T) gravity

In this article, we studied the behavior of relativistic spherical objects considering Tolman IV spacetime in modified $f(R,\,T)$ gravity for the uncharged perfect fluid matter. We have chosen the matter Lagrangian as $\mathcal{L}_m=-p$ to develop our present model. In particular, for this investigation we have reported for the compact object LMC $X-4$ [Mass=$(1.04 \pm 0.09)M_{\odot}$; Radius= $8.301_{-0.2}^{+0.2}$ Km] in our paper. The effect of the coupling parameter $\beta$ on the local matter distribution of compact stars has been investigated in this paper. It can be seen that with greater values of $\beta$, the sound speed and adiabatic index are higher. On contrary, the mass function takes lower value for higher values of $\beta$. Our obtained solution does not admit singularities in the matter density, pressure and metric functions. According to our graphical analysis, this new stellar model satisfies all physical requirements anticipated in a realistic star.

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arXiv2021

Phantom energy supported wormhole model in $f(R,\,T)$ gravity assuming conformal motion

In this article, we have discussed Morris and Thorne (MT) wormhole solutions in a modified theory of gravity that admits conformal motion. Here we explore the wormhole solutions in $f(R,\,T)$ gravity, which is a function of the Ricci scalar ($R$) and the trace of the stress-energy tensor ($T$). To study wormhole geometries, we make assumption of spherical symmetric static spacetime and the existence of conformal Killing symmetry to get more acceptable astrophysical outcomes. To do this, we choose the expression of $f(R,\,T)$ as $f(R,T)= R+2 \gamma T$. Here we employ the phantom energy EoS relating to radial pressure and density given by $p_r=\omega \rho$ with $\omega<-1$ to constrain our model. Following a discussion of wormhole geometry and behavior of shape function, the study moves on to the computation of proper radial distance, active mass function, the nature of total gravitational energy and a discussion on the violation of energy conditions. We have shown that the wormhole solutions exist for positive as well as negative values of the coupling constant $\gamma$. From our analysis we see that no wormhole solution exists for $\gamma =-4\pi,\,-\pi(3+\omega)$. All the physical parameters have been drawn by employing the values of $\gamma$ as $\gamma=-0.3,\,-0.2,\,-0.1,\,0,\,0.1$ and $0.2$, where $\gamma=0$ corresponds to general relativity (GR) case. It is found that for our proposed model, a realistic wormhole solutions satisfying all the properties can be obtained.

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arXiv2021

Stable and self consistent charged gravastar model within the framework of $f(R,\,T)$ gravity

In this work, we discuss the configuration of a gravastar (gravitational vacuum stars) in the context of $f(R, \,T )$ gravity by employing the Mazur-Mottola conjecture [P. Mazur and E. Mottola, Report No. LA-UR-01-5067; P. Mazur and E. Mottola, Proc. Natl. Acad. Sci. USA $101$, $9545$ ($2004$)]. Gravastar is conceptually a substitute for a black hole theory as available in literature and it has three regions with different equation of states. By assuming that the gravastar geometry admits conformal killing vector, the Einstein-Maxwell field equations have been solved in different regions of gravastar by taking a specific equation of state as proposed by Mazur and Mottola. We match our interior spacetime to the exterior spherical region which is completely vacuum and described by Reissner-Nordstr\"{o}m geometry. For a particular choice of $f(R,\,T)$ as $f(R, \,T )=R+2\gamma T$, here we analyze various physical properties of the thin shell and also presented our results graphically for these properties. The stability analysis of our present model is also studied by introducing a new parameter $\eta$ and we explored the stability regions. Our proposed gravastar model in presence of charge might be treated as a successful stable alternative of the charged black hole in the context of this gravity.

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arXiv2021

Relativistic compact stars in Tolman spacetime via an anisotropic approach

In this present work, we have obtained a singularity-free spherically symmetric stellar model with anisotropic pressure in the background of Einstein's general theory of relativity. The Einstein's field equations have been solved by exploiting Tolman {\em ansatz} [Richard C Tolman, Phys. Rev. 55:364, 1939] in $(3+1)$-dimensional space-time. Using observed values of mass and radius of the compact star PSR J1903+327, we have calculated the numerical values of all the constants from the boundary conditions. All the physical characteristics of the proposed model have been discussed both analytically and graphically. The new exact solution satisfies all the physical criteria for a realistic compact star. The matter variables are regular and well behaved throughout the stellar structure. Constraints on model parameters have been obtained. All the energy conditions are verified with the help of graphical representation. The stability condition of the present model has been described through different testings.

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arXiv2021

Compact stellar model in presence of pressure anisotropy in modified Finch Skea spacetime

A new model of anisotropic compact star is obtained in our present paper by assuming the pressure anisotropy. The proposed model is singularity free. The model is obtained by considering a physically reasonable choice for the metric potential $g_{rr}$ which depends on a dimensionless parameter `n'. The effect of $n$ is discussed numerically, analytically and through plotting. We have concentrated a wide range for n ($10\leq n \leq 1000$) for drawing the profiles of different physical parameters. The maximum allowable mass for different values of $n$ have been obtained by M-R plot. We have checked that the stability of the model is increased for larger value of $n$. For the viability of the model we have considered two compact stars PSR J1614-2230 and EXO 1785-248. We have shown that the expressions for the anisotropy factor and the metric component may serve as generating functions for uncharged stellar models in the context of the general theory of relativity.

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arXiv2021

Charged compact star in $f(R,T)$ gravity in Tolman-Kuchowicz spacetime

In this current study, our main focus is to model a specific charged compact star SAX J 1808.4-3658 (M = 0.88 $M_{\odot}$,\, R = 8.9 km) within the realm of $f(R,\,T)$ modified gravity theory using the metric potentials proposed by Tolman-Kuchowicz (Tolman, Phys Rev 55:364, 1939; Kuchowicz Acta Phys Pol 33:541, 1968) and the interior spacetime is matched to the exterior Reissner-Nordstr\"{o}m line element at the surface of the star. Tolman-Kuchowicz metric potentials provide a singularity-free solution which satisfies the stability criteria. Here we have used the simplified phenomenological MIT bag model equation of state (EoS) to solve Einstein-Maxwell field equations where the density profile ($\rho$) is related to the radial pressure ($p_r$) as $p_r(r) = (\rho - 4B_g)/3$. Further, to derive the values of unknown constants $a,\, b,\, B,\, C$ and the bag constant $B_g$, we match our interior space-time to the exterior Reissner-Nordstr\"{o}m line element at the surface of stellar system. In addition to this, to check the physical validity and stability of our suggested model, we evaluate some important properties such as effective energy density, effective pressures, radial and transverse sound velocities, relativistic adiabatic index, all energy conditions, compactness factor and surface redshift. It is depicted from our current study that all our derived results lie within the physically accepted regime which provides the viability of our present model in the context of $f(R,\,T)$ modified gravity.

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arXiv2021

Charged strange star in $f(R,T)$ gravity with linear equation of state

Our present study involves the strange stars model in the framework of $f(R,T)$ theory of gravitation. We have taken a linear function of the Ricci scalar $R$ and the trace $T$ of the stress-energy tensor $T_{\mu \nu}$ for the expression of $f(R,T)$, i.e., $f(R,T)=R+ 2 \gamma T $ to obtain the proposed model, where $\gamma$ is a coupling constant. Moreover, to solve the hydrostatic equilibrium equations, we consider a linear equation of state between the radial pressure $p_r$ and matter density $\rho$ as $p_r=\alpha \rho-\beta$, where $\alpha$ and $\beta$ are some positive constants, Both $\alpha,\,\beta$ depend on coupling constant $\gamma$ which have been also depicted in this paper. By employing the Krori-Barua {\em ansatz} already reported in the literature [J. Phys. A, Math. Gen. 8:508, 1975] we have found the solutions of the field equations in $f (R, T )$ gravity. The effect of coupling constant $\gamma$ have been studied on the model parameters like density, pressures, anisotropic factor, compactness, surface redshift, etc. both numerically and graphically. A suitable range for $\gamma$ is also obtained. The physical acceptability and stability of the stellar system have been tested by different physical tests, e.g., the causality condition, Herrera cracking concept, relativistic adiabatic index, energy conditions, etc. One can regain the solutions in Einstein gravity when $\gamma\rightarrow 0$

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