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 Quintessences compact star with Durgapal potential

2020 ◽  
Vol 35 (17) ◽  
pp. 2050144 ◽  
Author(s):  
Gabino Estevez-Delgado ◽  
Joaquin Estevez-Delgado ◽  
Aurelio Tamez Murguía ◽  
Rafael Soto-Espitia ◽  
Arthur Cleary-Balderas
Keyword(s):  
Compact Star ◽  
Radial Pressure ◽  
State Equation ◽  
Central Density ◽  
Star Model ◽  
Tangential Pressure ◽  
State Equations ◽  
Ordinary Matter ◽  
Linear State ◽  
Anisotropic Pressures

A compact star model formed by quintessence and ordinary matter is presented, both sources have anisotropic pressures and are described by linear state equations, also the state equation of the tangential pressure for the ordinary matter incorporates the effect of the quintessence. It is shown that depending on the compactness of the star [Formula: see text] the constant of proportionality [Formula: see text] between the density of the ordinary matter and the radial pressure, [Formula: see text], has an interval of values which is consistent with the possibility that the matter is formed by a mixture of particles like quarks, neutrons and electrons and not only by one type of them. The geometry is described by the Durgapal metric for [Formula: see text] and each one of the pressures and densities is positive, finite and monotonic decreasing, as well as satisfying the condition of causality and of stability [Formula: see text], which makes our model physically acceptable. The maximum compactness that we have is [Formula: see text], so we can apply our solution considering the observational data of mass and radii [Formula: see text], [Formula: see text] km which generate a compactness [Formula: see text] associated to the star PSR J0348[Formula: see text]+[Formula: see text]0432. In this case, the interval of [Formula: see text] and its maximum central density [Formula: see text] and in the surface [Formula: see text] of the star are [Formula: see text] and [Formula: see text], respectively, meanwhile the central density of the quintessence [Formula: see text].

An anisotropic charged fluids with Chaplygin equation of state

2021 ◽  
Vol 36 (21) ◽  
pp. 2150153
Author(s):  
Joaquin Estevez-Delgado ◽  
Noel Enrique Rodríguez Maya ◽  
José Martínez Peña ◽  
Arthur Cleary-Balderas ◽  
Jorge Mauricio Paulin-Fuentes
Keyword(s):  
Speed Of Sound ◽  
Radial Pressure ◽  
State Equation ◽  
Stellar Model ◽  
Compact Objects ◽  
Anisotropic Fluid ◽  
The Stability ◽  
Electrically Charged ◽  
Chaplygin Equation ◽  
Graphic Description

A stellar model with an electrically charged anisotropic fluid as a source of matter is presented. The radial pressure is described by a Chaplygin state equation, [Formula: see text], while the anisotropy [Formula: see text] is annulled in the center of the star [Formula: see text] is regular and [Formula: see text], the electric field, is also annulled in the center. The density pressures and the tangential speed of sound are regular, while the radial speed of sound is monotonically increasing. The model is physically acceptable and meets the stability criteria of Harrison–Zeldovich–Novikov and in respect of the cracking concept the solution is unstable in the region of the center and potentially stable near the surface. A graphic description is presented for the case of an object with a compactness rate [Formula: see text], mass [Formula: see text] and radius [Formula: see text] km that matches the star Vela X-1. Also, the interval of the central density [Formula: see text], which is consistent with the expected magnitudes for this type of stars, which shows that the behavior is accurate for describing compact objects.

scholarly journals Isotropic Stars in Higher-Order Torsion Scalar Theories

2016 ◽  
Vol 2016 ◽  
pp. 1-12 ◽  
Author(s):  
Gamal G. L. Nashed
Keyword(s):  
Killing Vector ◽  
Higher Order ◽  
Stellar Model ◽  
The Other ◽  
Conformal Killing ◽  
Spherically Symmetric ◽  
Field Equations ◽  
Torsion Scalar ◽  
Scalar Theories ◽  
Symmetric Spacetime

Two different nondiagonal tetrad spaces reproducing spherically symmetric spacetime are applied to the field equations of higher-order torsion scalar theories. Assuming the existence of conformal Killing vector, two isotropic solutions are derived. We show that the first solution is not stable while the second one confirms a stable behavior. We also discuss the construction of the stellar model and show that one of our solutions is capable of such construction while the other is not. Finally, we discuss the generalized Tolman-Oppenheimer-Volkoff and show that one of our models has a tendency to equilibrium.

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.

The two-body problem: an effective-one-body approach

2018 ◽  
Author(s):  
Nathalie Deruelle ◽  
Jean-Philippe Uzan
Keyword(s):  
Body Problem ◽  
Equations Of Motion ◽  
Reaction Force ◽  
Kerr Black Hole ◽  
Radiation Reaction ◽  
Spherically Symmetric ◽  
Geodesic Motion ◽  
Two Body Problem ◽  
Symmetric Spacetime ◽  
Radiation Reaction Force

This chapter presents the basics of the ‘effective-one-body’ approach to the two-body problem in general relativity. It also shows that the 2PN equations of motion can be mapped. This can be done by means of an appropriate canonical transformation, to a geodesic motion in a static, spherically symmetric spacetime, thus considerably simplifying the dynamics. Then, including the 2.5PN radiation reaction force in the (resummed) equations of motion, this chapter provides the waveform during the inspiral, merger, and ringdown phases of the coalescence of two non-spinning black holes into a final Kerr black hole. The chapter also comments on the current developments of this approach, which is instrumental in building the libraries of waveform templates that are needed to analyze the data collected by the current gravitational wave detectors.

scholarly journals Vaidya solutions in general covariant Hořava–Lifshitz gravity without projectability: Infrared limit

2014 ◽  
Vol 23 (08) ◽  
pp. 1450068 ◽  
Author(s):  
O. Goldoni ◽  
M. F. A. da Silva ◽  
G. Pinheiro ◽  
R. Chan
Keyword(s):  
General Relativity ◽  
Gauge Field ◽  
Radiation Field ◽  
Relativity Theory ◽  
Covariant Theory ◽  
Spherically Symmetric ◽  
Theory U ◽  
General Relativity Theory ◽  
Infrared Limit ◽  
Symmetric Spacetime

In this paper, we have studied nonstationary radiative spherically symmetric spacetime, in general covariant theory (U(1) extension) of Hořava–Lifshitz (HL) gravity without the projectability condition and in the infrared (IR) limit. The Newtonian prepotential φ was assumed null. We have shown that there is not the analogue of the Vaidya's solution in the Hořava–Lifshitz Theory (HLT), as we know in the General Relativity Theory (GRT). Therefore, we conclude that the gauge field A should interact with the null radiation field of the Vaidya's spacetime in the HLT.

scholarly journals Perihelion Precession and Deflection of Light in the General Spherically Symmetric Spacetime

2014 ◽  
Vol 2014 ◽  
pp. 1-7 ◽  
Author(s):  
Ya-Peng Hu ◽  
Hongsheng Zhang ◽  
Jun-Peng Hou ◽  
Liang-Zun Tang
Keyword(s):  
Solar System ◽  
Theoretical Result ◽  
Master Equation ◽  
Electric Charge ◽  
Spherically Symmetric ◽  
Experiment Data ◽  
Perihelion Precession ◽  
Deflection Of Light ◽  
Symmetric Spacetime ◽  
Spherically Symmetric Spacetime

The perihelion precession and deflection of light have been investigated in the 4-dimensional general spherically symmetric spacetime, and the master equation is obtained. As the application of this master equation, the Reissner-Nordstorm-AdS solution and Clifton-Barrow solution inf(R)gravity have been taken as examples. We find that both the electric charge andf(R)gravity can affect the perihelion precession and deflection of light, while the cosmological constant can only effect the perihelion precession. Moreover, we clarify a subtlety in the deflection of light in the solar system that the possible sun’s electric charge is usually used to interpret the gap between the experiment data and theoretical result. However, after also considering the effect from the sun’s same electric charge on the perihelion precession of Mercury, we can find that it is not the truth.

scholarly journals Anisotropic compact stars in higher-order curvature theory

2021 ◽  
Vol 81 (6) ◽  
Author(s):  
G. G. L. Nashed ◽  
S. D. Odintsov ◽  
V. K. Oikonomou
Keyword(s):  
General Relativity ◽  
Differential Equations ◽  
Higher Order ◽  
Specific Form ◽  
Ricci Scalar ◽  
Spherically Symmetric ◽  
Curvature Theory ◽  
Anisotropic Star ◽  
Symmetric Spacetime ◽  
Spherically Symmetric Spacetime

AbstractIn this paper we shall consider spherically symmetric spacetime solutions describing the interior of stellar compact objects, in the context of higher-order curvature theory of the $${{\mathrm {f(R)}}}$$ f ( R ) type. We shall derive the non-vacuum field equations of the higher-order curvature theory, without assuming any specific form of the $${{\mathrm {f(R)}}}$$ f ( R ) theory, specifying the analysis for a spherically symmetric spacetime with two unknown functions. We obtain a system of highly non-linear differential equations, which consists of four differential equations with six unknown functions. To solve such a system, we assume a specific form of metric potentials, using the Krori–Barua ansatz. We successfully solve the system of differential equations, and we derive all the components of the energy–momentum tensor. Moreover, we derive the non-trivial general form of $${{\mathrm {f(R)}}}$$ f ( R ) that may generate such solutions and calculate the dynamic Ricci scalar of the anisotropic star. Accordingly, we calculate the asymptotic form of the function $${\mathrm {f(R)}}$$ f ( R ) , which is a polynomial function. We match the derived interior solution with the exterior one, which was derived in [1], with the latter also resulting to a non-trivial form of the Ricci scalar. Notably but rather expected, the exterior solution differs from the Schwarzschild one in the context of general relativity. The matching procedure will eventually relate two constants with the mass and radius of the compact stellar object. We list the necessary conditions that any compact anisotropic star must satisfy and explain in detail that our model bypasses all of these conditions for a special compact star $$\textit{Her X--1}$$ Her X - - 1 , which has an estimated mass and radius $$(mass = 0.85 \pm 0.15M_{\circledcirc }\ and\ radius = 8.1 \pm 0.41~\text {km}$$ ( m a s s = 0.85 ± 0.15 M ⊚ a n d r a d i u s = 8.1 ± 0.41 km ). Moreover, we study the stability of this model by using the Tolman–Oppenheimer–Volkoff equation and adiabatic index, and we show that the considered model is different and more stable compared to the corresponding models in the context of general relativity.

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.

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