A study of anisotropic compact stars in f(R,ϕ,X) theory of gravity

2021 ◽  
Author(s):  
Adnan Malik ◽  
Iftikhar Ahmad ◽  
Kiran
Keyword(s):  
Modified Gravity ◽  
Scalar Potential ◽  
Radial Pressure ◽  
Compact Stars ◽  
Energy Conditions ◽  
Kinetic Term ◽  
Spherically Symmetric ◽  
Tangential Pressure ◽  
Equilibrium Conditions ◽  
Pressure Equilibrium

In this paper, we investigate the behavior of anisotropic compact stars in generalized modified gravity, namely [Formula: see text] gravity, where [Formula: see text] represents the Ricci scalar, [Formula: see text] is the scalar potential function and [Formula: see text] is a kinetic term of [Formula: see text]. We consider the spherically symmetric spacetime to analyze the feasible exposure of compact stars. We observe the behavior of anisotropic compact stars which includes Her X1, SAX J 1808.4-3658 and 4U 1820-30. From the graphical evaluation of energy density, tangential pressure, radial pressure, equilibrium conditions, energy conditions, mass–radius relationship, compactness and stability analysis of compact stars, it is concluded that the behavior of candidates of compact stars is regular in [Formula: see text] gravity for the considered parameter.

Wormhole solutions in modified f(R,φ,X) gravity

2021 ◽  
Vol 36 (04) ◽  
pp. 2150021
Author(s):  
M. Farasat Shamir ◽  
Adnan Malik ◽  
G. Mustafa
Keyword(s):  
Shape Function ◽  
Scalar Potential ◽  
Three Dimensional ◽  
State Parameter ◽  
Energy Conditions ◽  
Kinetic Term ◽  
Anisotropic Fluid ◽  
Shape Functions ◽  
Current Analysis ◽  
Static Space

This work aims to investigate the wormhole solutions in the background of [Formula: see text] theory of gravity, where [Formula: see text] is Ricci scalar, [Formula: see text] is scalar potential, and [Formula: see text] is the kinetic term. We consider spherically symmetric static space–time for exploring the wormhole geometry with anisotropic fluid. For our current analysis, we consider a particular equation of state parameter to study the behavior of traceless fluid and examine the physical behavior of energy density and pressure components. Furthermore, we also choose a particular shape function and explore the energy conditions. It can be noticed that energy conditions are violated for both shape functions. The violation of energy conditions indicates the existence of exotic matter and wormhole. Therefore, it can be concluded that our results are stable and realistic. The interesting feature of this work is to show two- and three-dimensional plotting for the analysis of wormhole geometry.

A generalized anisotropic model for super dense stars

2021 ◽  
pp. 2150070
Author(s):  
Joaquin Estevez-Delgado ◽  
Gabino Estevez-Delgado ◽  
Noel Enrique Rodríguez Maya ◽  
José Martínez Peña ◽  
Aurelio Tamez Murguía
Keyword(s):  
Radial Pressure ◽  
Compact Stars ◽  
Anisotropic Model ◽  
Speed Of Light ◽  
Matter Distribution ◽  
Sphere Model ◽  
Tangential Pressure ◽  
Relativistic Fluid ◽  
Causal Condition ◽  
Dense Stars

A static anisotropic relativistic fluid sphere model with regular geometry and finite hydrostatic functions is presented. In the interior of the sphere, the density, radial pressure and tangential pressure are positives, monotonically decreasing with increasing radius and the radial pressure vanishes at the surface of the matter distribution and is joined continuously to the exterior Schwarzschild’s solution at this surface. The speeds of the radial and tangential sound are positive and lower than the speed of light, that is, the causal condition is not violated, and also the behavior of these guarantees that the model is potentially stable. Furthermore, the range of the compactness ratio is characteristic of compact stars and it is shown that the effect of the anisotropy generates that the speed of the radial sound can behave as a function monotonically increasing or monotonically decreasing.

scholarly journals Analysis of charged compact stars in modified gravity

2018 ◽  
Vol 27 (08) ◽  
pp. 1850082 ◽  
Author(s):  
M. Farasat Shamir ◽  
Saeeda Zia
Keyword(s):  
Modified Gravity ◽  
Compact Star ◽  
Compact Object ◽  
Relative Difference ◽  
Comprehensive Analysis ◽  
Compact Stars ◽  
Energy Conditions ◽  
Anisotropic Pressure ◽  
Field Equations ◽  
Stability Energy

Current study highlights the physical characteristics of charged anisotropic compact stars by exploring some exact solutions of modified field equations in [Formula: see text] gravity. A comprehensive analysis is performed from the obtained solutions regarding stability, energy conditions, regularity, sound velocity and compactness. These solutions can be referred to model the compact celestial entities. In particular, a compact star named, [Formula: see text] has been modeled which indicates that current solution fits and is in conformity to the observational data as well. A useful and interesting fact from this model arises that relative difference between two forces of anisotropic pressure and electromagnetic force may occur inside the aforementioned compact star. This is another mechanism which is essential for stability of the compact object and prevent stellar object to annihilate.

scholarly journals Mimicking static anisotropic fluid spheres in general relativity

2016 ◽  
Vol 25 (02) ◽  
pp. 1650019 ◽  
Author(s):  
Petarpa Boonserm ◽  
Tritos Ngampitipan ◽  
Matt Visser
Keyword(s):  
Electromagnetic Field ◽  
Scalar Field ◽  
Charge Density ◽  
Perfect Fluid ◽  
Radial Pressure ◽  
Energy Conditions ◽  
Fluid Sphere ◽  
Anisotropic Fluid ◽  
Spherically Symmetric ◽  
Anisotropic Fluid Sphere

We argue that an arbitrary general relativistic static anisotropic fluid sphere, (static and spherically symmetric but with transverse pressure not equal to radial pressure), can nevertheless be successfully mimicked by suitable linear combinations of theoretically attractive and quite simple classical matter: a classical (charged) isotropic perfect fluid, a classical electromagnetic field and a classical (minimally coupled) scalar field. While the most general decomposition is not unique, a preferred minimal decomposition can be constructed that is unique. We show how the classical energy conditions for the anisotropic fluid sphere can be related to energy conditions for the isotropic perfect fluid, electromagnetic field, and scalar field components of the model. Furthermore, we show how this decomposition relates to the distribution of both electric charge density and scalar charge density throughout the model. The generalized TOV equation implies that the perfect fluid component in this model is automatically in internal equilibrium, with pressure forces, electric forces, and scalar forces balancing the gravitational pseudo-force. Consequently, we can build theoretically attractive matter models that can be used to mimic almost any static spherically symmetric spacetime.

GRAVITATIONAL COLLAPSE OF SPHERICALLY SYMMETRIC ANISOTROPIC FLUID WITH HOMOTHETIC SELF-SIMILARITY

2003 ◽  
Vol 12 (07) ◽  
pp. 1315-1332 ◽  
Author(s):  
C. F. C. BRANDT ◽  
M. F. A. DA SILVA ◽  
JAIME F. VILLAS DA ROCHA ◽  
R. CHAN
Keyword(s):  
Physical Properties ◽  
Gravitational Collapse ◽  
Energy Conditions ◽  
Anisotropic Fluid ◽  
Spherically Symmetric ◽  
Einstein Field Equations ◽  
Field Equations ◽  
Self Similarity ◽  
Tangential Pressure

We study spacetimes of spherically symmetric anisotropic fluid with homothetic self-similarity. We find a class of solutions to the Einstein field equations by assuming that the tangential pressure of the fluid is proportional to its radial one and that the fluid moves along time-like geodesics. The energy conditions, and geometrical and physical properties of these solutions are studied and found that some of them represent gravitational collapse of an anisotropic fluid.

scholarly journals Chaplygin strange stars in presence of quintessence

2021 ◽  
Vol 36 (29) ◽  
Author(s):  
Joaquin Estevez-Delgado ◽  
Modesto Pineda Duran ◽  
Arthur Cleary-Balderas ◽  
Noel Enrique Rodríguez Maya ◽  
José Martínez Peña
Keyword(s):  
Radial Pressure ◽  
State Equation ◽  
Stellar Model ◽  
Maximum Density ◽  
Spherically Symmetric ◽  
Tangential Pressure ◽  
Strange Stars ◽  
Ordinary Matter ◽  
Anisotropic Pressures ◽  
Symmetric Spacetime

Starting from a regular, static and spherically symmetric spacetime, we present a stellar model formed by two sources of ordinary and quintessence matter both with anisotropic pressures. The ordinary matter, with density [Formula: see text], is formed by a fluid with a state equation type Chaplygin [Formula: see text] for the radial pressure. And the quintessence matter, with density [Formula: see text], has a state equation [Formula: see text] for the radial pressure and [Formula: see text] for the tangential pressure with [Formula: see text]. The model satisfies the required conditions to be physically acceptable and additionally the solution is potentially stable, i.e. [Formula: see text] according to the cracking concept, and it also satisfies the Harrison–Zeldovich–Novikov criteria. We describe in a graphic manner the behavior of the solution for the case in which the mass is [Formula: see text] and radius [Formula: see text][Formula: see text]km which matches the star EXO 1785-248, from where we obtain the maximum density [Formula: see text] for the values of the parameters [Formula: see text], [Formula: see text].

scholarly journals Charged compact star in f(R, T) gravity in Tolman–Kuchowicz spacetime

2021 ◽  
Vol 81 (4) ◽  
Author(s):  
Pramit Rej ◽  
Piyali Bhar ◽  
Megan Govender
Keyword(s):  
Modified Gravity ◽  
Line Element ◽  
Compact Star ◽  
Stellar System ◽  
Radial Pressure ◽  
Energy Conditions ◽  
Field Equations ◽  
Compactness Factor ◽  
Physical Validity ◽  
The Stability

AbstractIn this current study, our main focus is on modeling the specific charged compact star SAX J 1808.4-3658 (M = 0.88 $$M_{\odot }$$ M ⊙ ,  R = 8.9 km) within the framework of $$f(R,\,T)$$ f ( R , T ) modified gravity theory using the metric potentials proposed by Tolman–Kuchowicz (Tolman in Phys Rev 55:364, 1939; Kuchowicz in 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 the Einstein–Maxwell field equations where the density profile ($$\rho $$ ρ ) is related to the radial pressure ($$p_{\mathrm{r}}$$ p r ) as $$p_{\mathrm{r}}(r) = (\rho - 4B_{\mathrm{g}})/3$$ p r ( r ) = ( ρ - 4 B g ) / 3 . Furthermore, to derive the values of the unknown constants $$a,\, b,\, B,\, C$$ a , b , B , C and the bag constant $$B_{\mathrm{g}}$$ B g , we match our interior spacetime to the exterior Reissner–Nordström line element at the surface of stellar system. In addition, 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 shows the viability of our present model in the context of $$f(R,\,T)$$ f ( R , T ) modified gravity.

scholarly journals Conformally symmetric relativistic star

2017 ◽  
Vol 32 (08) ◽  
pp. 1750053 ◽  
Author(s):  
Farook Rahaman ◽  
Sunil D. Maharaj ◽  
Iftikar Hossain Sardar ◽  
Koushik Chakraborty
Keyword(s):  
Conformal Symmetry ◽  
Compact Object ◽  
Radial Pressure ◽  
Compact Stars ◽  
Energy Conditions ◽  
Anisotropic Pressure ◽  
Matter Distribution ◽  
Strong Energy ◽  
Principal Directions ◽  
The Masses

We investigate whether compact stars having Tolman-like interior geometry admit conformal symmetry. Taking anisotropic pressure along the two principal directions within the compact object, we obtain physically relevant quantities such as transverse and radial pressure, density and redshift function. We study the equation of state (EOS) for the matter distribution inside the star. From the relation between pressure and density function of the constituent matter, we explore the nature and properties of the interior matter. The redshift function and compactness parameter are found to be physically reasonable. The matter inside the star satisfies the null, weak and strong energy conditions. Finally, we compare the masses and radii predicted from the model with corresponding values in some observed stars.

scholarly journals Some specific wormhole solutions in f(R)-modified gravity theory

2021 ◽  
pp. 2150024
Author(s):  
Bikram Ghosh ◽  
Saugata Mitra ◽  
Subenoy Chakraborty
Keyword(s):  
Modified Gravity ◽  
Shape Function ◽  
Matter Field ◽  
Gravity Theory ◽  
Energy Conditions ◽  
Spherically Symmetric ◽  
Shape Functions ◽  
Matter Distribution ◽  
Anisotropic Matter ◽  
Modified Gravity Theory

The paper deals with the static spherically symmetric wormhole solutions in [Formula: see text]-modified gravity theory with anisotropic matter field and for some particular choices for the shape functions. This work may be considered as an extension of the general formalism in [S. Halder, S. Bhattacharya and S. Chakraborty, Phys. Lett. B 791, 270 (2019)] for finding wormhole solutions. For isotropic matter distribution it has been shown that wormhole solutions are possible for zero tidal force and it modifies the claim in [M. Cataldo, L. Leimpi and P. Rodriguez, Phys. Lett. B 757, 130 (2016)]. Finally, energy conditions are examined and it is found that all energy conditions are satisfied in a particular domain with a particular choice of the shape function.

scholarly journals Traversable wormhole in logarithmic f(R) gravity by various shape and redshift functions

2022 ◽  
Author(s):  
Jafar Sadeghi ◽  
Mehdi Shokri ◽  
Saeed Noori Gashti ◽  
Behnam Pourhassan ◽  
Prabir Rudra
Keyword(s):  
Energy Condition ◽  
Radial Pressure ◽  
Null Energy Condition ◽  
Energy Conditions ◽  
Dominant Energy Condition ◽  
Tangential Pressure ◽  
Strong Energy Condition ◽  
Traversable Wormhole ◽  
Strong Energy ◽  
Text Model

In this paper, we study the traversable wormhole solutions for a logarithmic corrected [Formula: see text] model by considering two different statements of shape [Formula: see text] and redshift [Formula: see text] functions. We calculate the parameters of the model including energy density [Formula: see text], tangential pressure [Formula: see text] and radial pressure [Formula: see text] for the corresponding forms of the functions. Then, we investigate different energy conditions such as null energy condition, weak energy condition, dominant energy condition and strong energy condition for our considered cases. Finally, we explain the satisfactory conditions of energy of the models by related plots.

Sign in / Sign up

Export Citation Format

Share Document