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Piyali Bhar

Publications and source records attributed to Piyali Bhar.

At least 37 records · Page 2Linked to original sources
arXiv2021

Charged gravastar model in $f(T)$ gravity admitting conformal motion

In this paper, model of charged gravastar under $f(T)$ modified gravity is obtained. The model has been explored by taking the diagonal tetrad field of static spacetime together with electric charge. To solve the Einstein-Maxwell field equations, along with $f(T)$ gravity, we assume the existence of a conformal Killing vector which relates between geometry and matter through the Einstein-Maxwell field equations by an inheritance symmetry. We study several cases of interest to explore physically valid features of the solutions. Some physical properties of the model are discussed and we match our interior spacetime to the exterior Reissner-Nordström spacetime in presence of thin shell.

gr-qc↗
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 $T_{μν}$ for the expression of $f(R,T)$, i.e., $f(R,T)=R+ 2 γT $ to obtain the proposed model, where $γ$ 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 $ρ$ as $p_r=αρ-β$, where $α$ and $β$ are some positive constants, Both $α,\,β$ depend on coupling constant $γ$ 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 $γ$ have been studied on the model parameters like density, pressures, anisotropic factor, compactness, surface redshift, etc. both numerically and graphically. A suitable range for $γ$ 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 $γ\rightarrow 0$

gr-qc↗
arXiv2021

Charged strange star with Krori-Barua potential in $f(R,T)$ gravity admitting Chaplygin equation of state

In present paper a new compact star model in f(R,T) gravity is obtained where R and T denote the Ricci scalar and the trace of energy-momentum tensor $T_{μν}$ respectively. To develop the model we consider the spherically symmetric space-time along with anisotropic fluid distribution in presence of electric field with $f(R,T) = R + 2γT$ where $γ$ is a small positive constant. We have used the Chaplygin equation of state to explore the stellar model. The field equations for $f(R,T)$ gravity have been solved by employing the Krori-Barua ansatz already reported in literature [J. Phys. A, Math. Gen. 8:508, 1975]. The exterior spacetime is described by Reissner-Nordstrom line element for smooth matching at the boundary. It is worthwhile to mention here that the values of all the constants involved with this model have been calculated for the strange stars 4U 1538-52 for different values of γ with the help of matching conditions. The acceptability of the model is discussed in details both analytically and graphically by studying the physical attributes of matter density, pressures, anisotropy factor, stability etc. We have also obtained the numerical values in tabular form for central density, surface density, central pressure and central adiabatic index for different values of $γ$. The solutions of the field equations in Einstein gravity can be regained by simply putting $γ= 0$ to our solution. Moreover, the proposed model is shown to be physically admissible and corroborate with experimental observations on strange star candidates such as 4U 1538-52.

gr-qc↗
arXiv2021

Strange star with Krori-Barua potential in presence of anisotropy

In present paper a well-behaved new model of anisotropic compact star in (3+1)-dimensional spacetime has been investigated in the background of Einstein's general theory of relativity. The model has been developed by choosing $g_rr$ component as Krori-Barua (KB) ansatz [Krori and Barua in J. Phys. A, Math. Gen. 8:508, 1975]. The field equations have been solved by a proper choice of the anisotropy factor which is physically reasonable and well behaved inside the stellar interior. Interior spacetime has been matched smoothly to the exterior Schwarzschild vacuum solution and it has also been depicted graphically. Model is free from all types of singularities and is in static equilibrium under different forces acting on the system. The stability of the model has been tested with the help of various conditions available in literature. The solution is compatible with observed masses and radii of a few compact stars.

gr-qc↗
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.

gr-qc↗
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-Nordström 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 ($ρ$) is related to the radial pressure ($p_r$) as $p_r(r) = (ρ- 4B_g)/3$. 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-Nordström 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.

gr-qc↗
arXiv2021

Finch-Skea star model in f(R, T ) theory of gravity

The present work discusses about the existence of compact star model in the context of $f(R,T)$ gravity with $R$ as the Ricci scalar and $T$ as the trace of energy-momentum tensor $T_{μν}$. The model has been developed by considering the spherically symmetric spacetime consisting of isotropic fluid with $f(R,T)=R+2 βT$ with $β$ be the coupling parameter. The corresponding field equations are solved by choosing well known Finch-Skea {\em ansatz} [Finch, M.R., Skea, J.E.F.:{\it Class. Quantum Gravity} {\bf 6}, 467 (1989)]. For spacetime continuity we elaborate the boundary conditions by considering the exterior region as Schwarzschild metric. The unknown constants appearing in the solution are evaluated for the compact star PSR~J 1614-2230 for different values of coupling constant. The physical properties of the model, e.g., matter density, pressure, stability etc. have been discussed both analytically and graphically. This analysis showed that the geometry and matter are compatible with each other as well as the model is in stable equilibrium in the context of $f(R,\,T)$ modified gravity.

gr-qc↗
arXiv2020

Compact stellar model in Tolman space-time in presence of pressure anisotropy

In this paper, we develop a new relativistic compact stellar model for a spherically symmetric anisotropic matter distribution. The model has been obtained through generating a new class of solutions by invoking the Tolman {\em ansatz} for one of the metric potentials $g_{rr}$ and a physically reasonable selective profile of radial pressure. We have matched our obtained interior solution to the Schwarzschild exterior spacetime over the bounding surface of the compact star. These matching conditions together with the condition of vanishing the radial pressure across the boundary of the star have been utilized to determine the model parameters. We have shown that the central pressure of the star depends on the parameter $p_0$. We have estimated the range of $p_0$ by using the recent data of compact stars 4U 1608-52 and Vela X-1. The effect of $p_0$ on different physical parameters e.g., pressure anisotropy, the subliminal velocity of sound, relativistic adiabatic index etc. have also been discussed. The developed model of the compact star is elaborately discussed both analytically and graphically to justify that it satisfies all the criteria demanded a realistic star. From our analysis, we have shown that the effect of anisotropy becomes small for higher values of $p_0$. The mass-radius (M-R) relationship which indicates the maximum mass admissible for observed pulsars for a given surface density has also been investigated in our model. Moreover, the variation of radius and mass with central density has been shown which allow us to estimate central density for a given radius (or mass) of a compact star.

gr-qc↗
arXiv2020

Durgapal IV model in light of the minimal geometric deformation approach

The present article is devoted to the study of local anisotropies effects on the Durgapal's fourth model in the context of gravitational decoupling via the Minimal Geometric Deformation approach. To do it, the most general equation of state relating the components of the $θ$--sector is imposed to obtain the decoupler function $f(r)$. In addition, certain properties of the obtained solution are investigated, such as the behavior of the salient material content threading the stellar interior, causality and energy conditions, hydrostatic balance through modified Tolman--Oppenheimer--Volkoff conservation equation and stability mechanism against local anisotropies by means of adiabatic index, sound velocity of the pressure waves, convection factor and Harrison--Zeldovich--Novikov procedure, in order to check if the model is physically admissible or not. Regarding the stability analysis, it is found that the model presents unstable regions when the sound speed of the pressure waves and convection factor are used in distinction with what happens in the adiabatic index and Harrison--Zeldovich--Novikov case. To produce a more realistic picture the numerical data for some known compact objects was placed and different values of the parameter $α$ were considered to compare with the GR case ı.e, $α=0$.

gr-qc↗
arXiv2019

Compact star in Tolman Kuchowicz spacetime in background of Einstein Gauss Bonnet gravity

The present work is devoted to the study of anisotropic compact matter distributions within the framework of 5-dimensional Einstein-Gauss-Bonnet gravity. To solve the field equations, we have considered that the inner geometry is described by Tolman-Kuchowicz spacetime. The Gauss-Bonnet Lagrangian is coupled to Einstein-Hilbert action through a coupling constant. When this coupling tends to zero general relativity results are recovered. We analyze the effect of this parameter on the principal salient features of the model, such as energy density, radial and tangential pressure and anisotropy factor.Additionally, the behaviour of the subliminal sound speed of the pressure waves in the principal direction of the configuration and the conduct of the energy-momentum tensor throughout the star are analyzed employing causality condition and energy conditions, respectively. All these subjects are supported by mean of physical, mathematical and graphical survey

physics.gen-ph↗
arXiv2017

Dark energy stars: Stable configurations

In present paper a spherically symmetric stellar configuration has been analyzed by assuming the matter distribution of the stellar configuration is anisotropic in nature and compared with the realistic objects, namely, the low mass X-ray binaries (LMXBs) and X-ray pulsars. The analytic solution has been obtained by utilizing the dark energy equation of state for the interior solution corresponding to the Schwarzschild exterior vacuum solution at the junction interface. Several physical properties like energy conditions, stability, mass-radius ratio, and surface redshift are described through mathematical calculations as well as graphical plots. It is found that obtained mass-radius ration of the compact stars candidates like 4U 1820-30, PSR J 1614-2230, Vela X-1 and Cen X-3 are very much consistent with the observed data by Gangopadhyay et al. (Mon. Not. R. Astron. Soc. 431, 3216 (2013)). So our proposed model would be useful in the investigation of the possible clustering of dark energy.

gr-qc↗
arXiv2017

Charged compact star model in Einstein-Maxwell-Gauss-Bonnet gravity

Present paper provides a model of static charged anisotropic fluid sphere in the EinsteinMaxwell- GaussBonnet (EMGB) theory of gravitation. We select KB anstz as the metric co-efficient along with electric field intensity. To develop our model we assume a linear EoS between the radial pressure and the matter density. The model obtained here is found to satisfy the elementary physical requirements like non-negativity nature of pressure and density, the energy conditions, continuity of the metric co-efficients, subliminal velocity of sound and also pressure free hypersurface etc. It may also noted that the solution is free from any kind of singularities.

physics.gen-ph↗
arXiv2017

A charged anisotropic well-behaved Adler-Finch-Skea solution Satisfying Karmarkar Condition

In the present article, we discover a new well-behaved charged anisotropic solution of Einstein-Maxwell's field equations. We ansatz the metric potential $g_{00}$ of the form given by Maurya el al. (arXiv:1607.05582v1) with $n=2$. In their article it is mentioned that for $n=2$ the solution is not well-behaved for neutral configuration as the speed of sound is non-decreasing radially outward. However, the solution can represent a physically possible configuration with the inclusion of some net electric charged i.e. the solution can become a well-behaved solution with decreasing sound speed radially outward for a charged configuration. Due to the inclusion of electric charged the solution leads to a very stiff equation of state (EoS) with the velocity of sound at the center $v_{r0}^2=0.819, ~v_{t0}^2=0.923$ and the compactness parameter $u=0.823$ is closed to the Buchdahl limit 0.889. This stiff EoS support a compact star configuration of mass $5.418M_\odot$ and radius of $10.1 km$.

physics.gen-ph↗
arXiv2017

A new class of relativistic model of compact stars of embedding class I

In the present paper we have constructed a new relativistic anisotropic compact star model having a spherically symmetric metric of embedding class one. Here we have assumed an arbitrary form of metric function and solved the Einstein relativistic field equations with the help of Karmarkar condition for an anisotropic matter distri- bution. The physical properties of our model such as pressure, density, mass function, surface red-shift, gravitational red-shift are investigated and the stability of the stellar configuration is discussed in details. Our model is free from central singularities and satisfies all energy conditions. The model we present here satisfy the static stability criterion.

gr-qc↗
arXiv2016

A New Class of Anisotropic Charged Compact Star

A new model of charged compact star is reported by solving the Einstein-Maxwell field equations by choosing a suitable form of radial pressure. The model parameters $ρ$, $p_r$, $p_{\perp}$ and $E^{2}$ are in closed form and all are well behaved inside the stellar interior. A comparative study of charged and uncharged model is done with the help of graphical analysis.

gr-qc↗
arXiv2016

Wormhole supported by dark energy admitting conformal motion

In this article, we study the possibility of sustaining a static and spherically symmetric traversable wormhole geometries admitting conformal motion in Einstein gravity, which presents a more systematic approach to search a relation between matter and geometry. In wormhole physics, the presence of exotic matter is a fundamental ingredient and we show that this exotic source can be dark energy type which support the existence of wormhole spacetimes. In this work we model a wormhole supported by dark energy which admits conformal motion. We also discuss the possibility of detection of wormholes in the outer regions of galactic halos by means of gravitational lensing. The studies of the total gravitational energy for the exotic matter inside a static wormhole configuration are also done.

gr-qc↗
arXiv2016

Modelling of anisotropic compact stars of emebedding class one

In the present article, we have constructed static anisotropic compact star models of Einstein field equations for the spherical symmetric metric of embedding class one. By assuming the particular form of metric function $ν$, We have solved the Einstein field equations for anisotropic matter distribution. The anisotropic models are representing the realistic compact objects such as SAX J 1808.4-3658 (SS1), Her X - 1, Vela X-12, PSR J1614-2230 and Cen X - 3. We have reported our results in details for compact star Her X-1 on the ground of physical properties such as pressure, density, velocity of sound, energy conditions, TOV equation and red-shift etc. Along with these, we have also discussed about stability of the compact star models. Finally we made the comparison between our anisotropic stars with the realistic objects on the key aspects as central density, central pressure, compactness and surface red-shift.

gr-qc↗