Stellar model for anisotropic compact stars in Schwarzchild’s coordinates

2021 ◽  
Vol 104 (8) ◽  
Author(s):  
Jitendra Kumar ◽  
Puja Bharti
Keyword(s):  
Stellar Model ◽  
Compact Stars

scholarly journals An analytical anisotropic compact stellar model of embedding class I

2021 ◽  
Vol 36 (05) ◽  
pp. 2150028
Author(s):  
Lipi Baskey ◽  
Shyam Das ◽  
Farook Rahaman
Keyword(s):  
Radial Pressure ◽  
Stellar Model ◽  
Compact Objects ◽  
Compact Stars ◽  
Model Parameters ◽  
Field Equations ◽  
Principal Stresses ◽  
Schwarzschild Solution ◽  
Spherical Fluid ◽  
Physical Profile

A class of solutions of Einstein field equations satisfying Karmarkar embedding condition is presented which could describe static, spherical fluid configurations, and could serve as models for compact stars. The fluid under consideration has unequal principal stresses i.e. fluid is locally anisotropic. A certain physically motivated geometry of metric potential has been chosen and codependency of the metric potentials outlines the formation of the model. The exterior spacetime is assumed as described by the exterior Schwarzschild solution. The smooth matching of the interior to the exterior Schwarzschild spacetime metric across the boundary and the condition that radial pressure is zero across the boundary lead us to determine the model parameters. Physical requirements and stability analysis of the model demanded for a physically realistic star are satisfied. The developed model has been investigated graphically by exploring data from some of the known compact objects. The mass-radius (M-R) relationship that shows the maximum mass admissible for observed pulsars for a given surface density has also been investigated. Moreover, the physical profile of the moment of inertia (I) thus obtained from the solutions is confirmed by the Bejger–Haensel concept.

Analysis of compact stars in logarithmic-corrected R2 gravity

2019 ◽  
Vol 35 (02) ◽  
pp. 1950354 ◽  
Author(s):  
M. Farasat Shamir ◽  
Iffat Fayyaz
Keyword(s):  
Graphical Representation ◽  
Stellar Model ◽  
Compact Stars ◽  
Energy Conditions ◽  
Einstein Field Equations ◽  
Field Equations ◽  
Logarithmic Corrections ◽  
Proposed Model ◽  
Physical Tests ◽  
Surface Redshift

We discuss the existence of compact stars in the context of [Formula: see text] gravity model, where additional logarithmic corrections are assumed. Here, [Formula: see text] is the Ricci scalar and [Formula: see text], [Formula: see text] are constant values. Further, the compact stars are considered to be anisotropic in nature, due to the spherical symmetry and high density. For this purpose, we derive the Einstein field equations by considering Krori–Barua spacetime. For our proposed model, the physical acceptability is verified by employing several physical tests like the energy conditions, Herrera cracking concept and stability condition. In addition to this, we also discuss some important properties such as mass–radius relation, surface redshift and the speed of sound are analyzed. Our results are compared with observational stellar mass data, namely, 4U 1820-30, Cen X-3, EXO 1785-248 and LMC X-4. The graphical representation of obtained solutions provide strong evidences for more realistic and viable stellar model.

scholarly journals A charged perfect fluid model with high compactness

2019 ◽  
Vol 65 (4 Jul-Aug) ◽  
pp. 382 ◽  
Author(s):  
G. Estevez-Delgado ◽  
J. Estevez-Delgado ◽  
M. Pineda Duran ◽  
N. Montelongo García ◽  
J.M. Paulin-Fuentes
Keyword(s):  
Electric Field ◽  
Perfect Fluid ◽  
Maxwell Equations ◽  
Fluid Model ◽  
Stellar Model ◽  
Compact Stars ◽  
Charged Fluid ◽  
Charge Parameter ◽  
Positive Functions ◽  
Increasing Function

A relativistic, static and spherically symmetrical stellar model is presented, constituted by a perfect charged fluid. This represents a generalization to the case of a perfect neutral fluid, whose construction is made through the solution to the Einstein-Maxwell equations proposing a form of gravitational potential  $g_{tt}$ and the electric field. The choice of electric field implies that this model supports values of compactness$u=GM/c^2R\leq 0.5337972212$, values higher than the case without electric charge ($u\leq 0.3581350065$), being this feature of relevance to get to represent compact stars. In addition, density and pressure are positive functions, bounded and decreasing monotones, the electric field is a monotonously increasing function as well as satisfying the condition of causality so the model is physically acceptable. In a complementary way, the internal behavior of the hydrostatic functions and their values are obtained taking as a data the corresponding to a star of $1 M_\odot$,for different values of the charge parameter, obtaining an interval for the central density $\rho_c\approx (7.9545,2.7279) 10^{19}$ $ Kg/m^3$ characteristic of compact stars.

Compact stars

2018 ◽  
Vol 33 (15) ◽  
pp. 1850081 ◽  
Author(s):  
Gabino Estevez-Delgado ◽  
Joaquin Estevez-Delgado
Keyword(s):  
Speed Of Sound ◽  
Anisotropy Parameter ◽  
Compact Object ◽  
Stellar Model ◽  
Compact Stars ◽  
Central Density ◽  
Speeds Of Sound ◽  
Light Speed ◽  
Maximum Value ◽  
Two Parameters

An analysis and construction is presented for a stellar model characterized by two parameters (w, n) associated with the compactness ratio and anisotropy, respectively. The reliability range for the parameter w [Formula: see text] 1.97981225149 corresponds with a compactness ratio u [Formula: see text] 0.2644959374, the density and pressures are positive, regular and monotonic decrescent functions, the radial and tangential speed of sound are lower than the light speed, moreover, than the plausible stability. The behavior of the speeds of sound are determinate for the anisotropy parameter n, admitting a subinterval where the speeds are monotonic crescent functions and other where we have monotonic decrescent functions for the same speeds, both cases describing a compact object that is also potentially stable. In the bigger value for the observational mass M = 2.05 M[Formula: see text] and radii R = 12.957 Km for the star PSR J0348+0432, the model indicates that the maximum central density [Formula: see text] = 1.283820319 × 10[Formula: see text] Kg/m3 corresponds to the maximum value of the anisotropy parameter and the radial and tangential speed of the sound are monotonic decrescent functions.

A uniparametric perfect fluid solution to represent compact stars

2021 ◽  
Vol 36 (10) ◽  
pp. 2150068
Author(s):  
Joaquin Estevez-Delgado ◽  
Noel Enrique Rodríguez Maya ◽  
José Martínez Peña ◽  
David Rivera Rangel ◽  
Nancy Cambron Muñoz
Keyword(s):  
Neutron Stars ◽  
Perfect Fluid ◽  
Stellar Model ◽  
Compact Objects ◽  
Compact Stars ◽  
Index Formula ◽  
Perfect Fluid Solution ◽  
Gravitational Theories ◽  
State Formula ◽  
The Stability

In the description of neutron stars, it is very important to consider gravitational theories as general relativity, due to the determining influence on the behavior of the different types of stars, since some objects show densities even bigger than nuclear density. This paper starts with Einstein’s equations for a perfect fluid and then we present a uniparametric stellar model which allows to describe compact objects like neutron stars with compactness ratio [Formula: see text]. The pressure and density are monotone decreasing regular functions, the speed of sound satisfies the causality condition, while the value for its adiabatic index [Formula: see text] guarantees the stability. In addition, the graph of [Formula: see text] versus [Formula: see text] shows a quasi-linear relationship for the equation of state [Formula: see text], which is similar to the so-called MIT Bag equation when we have the interaction between quarks. In our case it is due to the interaction of the different components found inside the star, such as electrons and neutrons. As an application of the model, we describe the star PSR J1614-2230 with a observed mass of [Formula: see text] and a radius [Formula: see text], the model shows that the maximum central density occurs for a maximal compactness value [Formula: see text].

scholarly journals Anisotropic strange star with Tolman V potential

2018 ◽  
Vol 27 (08) ◽  
pp. 1850089 ◽  
Author(s):  
Dibyendu Shee ◽  
Debabrata Deb ◽  
Shounak Ghosh ◽  
Saibal Ray ◽  
B. K. Guha
Keyword(s):  
Stellar System ◽  
Energy Condition ◽  
Anisotropy Parameter ◽  
Stellar Model ◽  
Compact Stars ◽  
Anisotropic Fluid ◽  
Physical Parameters ◽  
Model Matching ◽  
Field Equations ◽  
Bag Constant

In this paper, we present a strange stellar model using Tolman [Formula: see text]-type metric potential employing simplest form of the MIT bag equation of state (EOS) for the quark matter. We consider that the stellar system is spherically symmetric, compact and made of an anisotropic fluid. Choosing different values of [Formula: see text] we obtain exact solutions of the Einstein field equations and finally conclude that for a specific value of the parameter [Formula: see text], we find physically acceptable features of the stellar object. Further, we conduct different physical tests, viz., the energy condition, generalized Tolman–Oppeheimer–Volkoff (TOV) equation, Herrera’s cracking concept, etc., to confirm the physical validity of the presented model. Matching conditions provide expressions for different constants whereas maximization of the anisotropy parameter provides bag constant. By using the observed data of several compact stars, we derive exact values of some of the physical parameters and exhibit their features in tabular form. It is to note that our predicted value of the bag constant satisfies the report of CERN-SPS and RHIC.

scholarly journals NLTE Model Atmospheres for Extremely Hot Compact Stars

2000 ◽  
Vol 195 ◽  
pp. 423-424
Author(s):  
T. Rauch ◽  
J. L. Deetjen ◽  
S. Dreizler ◽  
K. Werner
Keyword(s):  
Signal To Noise Ratio ◽  
Far Infrared ◽  
Model Atmosphere ◽  
Stellar Model ◽  
Compact Stars ◽  
Local Thermal Equilibrium ◽  
High Signal ◽  
X Rays ◽  
Metal Line ◽  
Stellar Spectra

Present observational techniques provide stellar spectra with high resolution at a high signal-to-noise ratio over the complete wavelength range—from the far infrared to X-rays.The effects of Non-“Local Thermal Equilibrium” (NLTE) are particularly important for hot stars, hence the use of reliable NLTE stellar model atmosphere fluxes is required for an adequate spectral analysis.State-of-the-art NLTE model atmospheres include metal-line blanketing of millions of lines of all elements from hydrogen up to the iron-group elements, and thus permit precise analyses of extremely hot compact stars, e.g., central stars of planetary nebulae, PG 1159 stars, white dwarfs, and neutron stars. Their careful spectroscopic study is of great interest in several branches of modern astrophysics, e.g., stellar and galactic evolution, and interstellar matter.

A study of anisotropic compact stars based on embedding class 1 condition

2019 ◽  
Vol 28 (09) ◽  
pp. 1950116 ◽  
Author(s):  
S. K. Maurya ◽  
Debabrata Deb ◽  
Saibal Ray ◽  
P. K. F. Kuhfittig
Keyword(s):  
Stellar Model ◽  
Einstein Equations ◽  
Compact Stars ◽  
Energy Conditions ◽  
Physical Parameters ◽  
Matter Distribution ◽  
Generalized Model ◽  
Anisotropic Factor ◽  
Class 1 ◽  
Metric Functions

This paper discusses a generalized model for compact stars, assumed to be anisotropic in nature due to the presence of highly dense and ultra-relativistic matter distribution. After embedding the 4D Riemannian space locally and isometrically into a 5D pseudo-Euclidean space, we solve the Einstein equations by employing a class of physically acceptable metric functions. The physical properties determined include the anisotropic factor showing that the anisotropy is zero at the center and maximum at the surface. Other boundary conditions yield the values of various parameters needed for rendering the numerous plots and also led to the EOS parameters. It is further determined that the usual energy conditions are satisfied and that the compact structures are stable, based on several criteria, viz., the equilibrium of forces, Herrera cracking concept, adiabatic index, etc. We note that the proposed stellar model satisfies the Buchdahl condition. Finally, the values of the numerous constants and physical parameters are determined, specifically for the compact stellar object [Formula: see text], which we choose as a representative of the compact stars to present the analysis of the obtained results. Finally, we show that the present generalized model can justify most of the compact stars including white dwarfs and ultra-dense compact stars for a suitable tuning of the parametric values of [Formula: see text].

An isotropic analytical model for charged stars

2021 ◽  
pp. 2150089
Author(s):  
Joaquin Estevez-Delgado ◽  
Gabino Estevez-Delgado ◽  
Noel Enrique Rodríguez Maya ◽  
José Martínez Peña ◽  
Modesto Pineda Duran
Keyword(s):  
Speed Of Sound ◽  
Stellar Model ◽  
Compact Stars ◽  
Spherically Symmetric ◽  
Model Case ◽  
Charged Fluid ◽  
Two Parameters ◽  
Charged Model ◽  
Increasing Function ◽  
Investigation Report

In this investigation report, we present a perfect charged fluid solution for a static and spherically symmetric spacetime; for its construction, we suppose a metric potential, [Formula: see text], and a specific form of the electric field’s intensity, [Formula: see text], in such a manner that the resulting stellar model is physically acceptable and stable. The model presented depends on two parameters [Formula: see text] related to the compactness and the magnitude of the electric field and these same parameters will generate different possibilities for the behavior of the speed of sound. For the particular case in which [Formula: see text], we obtain once more a chargeless model constructed previously, the compactness for the charged model case is greater than in the chargeless case. As an effect of the charge, the model admits two regions for the parameter [Formula: see text], in one of these the speed of sound is a monotonic decreasing function and in the other it is a monotonic increasing function. By means of a numerical analysis, it is shown that the orders of magnitude associated to the pressure and density are characteristic of the compact stars. In particular for [Formula: see text], the range of [Formula: see text], which implies that the radius of an object with mass [Formula: see text] is found between 6554.620 m and 7672.702 m with a maximum central density of [Formula: see text].

Exploring physical features of anisotropic quark stars in Brans-Dicke theory with a massive scalar field via embedding approach

2021 ◽  
Author(s):  
Abdelghani Errehymy ◽  
G. Mustafa ◽  
Youssef Khedif ◽  
Mohammed Daoud
Keyword(s):  
Scalar Field ◽  
Coupling Parameter ◽  
Stellar System ◽  
Stellar Model ◽  
Compact Stars ◽  
Energy Conditions ◽  
Field Equations ◽  
Massive Scalar Field ◽  
Quark Stars ◽  
Free Fermi

Abstract The main aim of this manuscript is to explore the existence and salient features of spherically symmetric relativistic quark stars in the background of massive Brans-Dicke gravity. The exact solutions to the modified Einstein field equations are derived for specific forms of coupling and scalar field functions by using the equation of state relating to the strange quark matter that stimulates the phenomenological MIT-Bag model as a free Fermi gas of quarks. We use a well-behaved function along with Karmarkar condition for class-one embedding as well as junction conditions to determine the unknown metric tensors. The radii of the strange compact stars viz., PSR J1416-2230, PSR J1903+327, 4U 1820-30, CenX-3, EXO1785-248 are predicted via their observed mass for different values of the massive Brans-Dicke parameters. We explore the influences of mass of scalar field $m_{\phi}$ as well as coupling parameter $\omega_{BD}$ along with bag constant $\mathcal{B}$ on state determinants and perform several tests on the viability and stability of the constructed stellar model. Conclusively, we find that our stellar system is physically viable and stable as it satisfies all the energy conditions as well as necessary stability criteria under the influence of a gravitational scalar field.

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