Non-trivial class of anisotropic compact stellar model in Rastall gravity

Nashed, G. G. L.; Hanafy, W. El

doi:10.1140/epjc/s10052-022-10634-0

Cited by 41 publications

(14 citation statements)

References 124 publications

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“…Remarkably, the matter-geometry coupling due to the trace T does not contribute to the anisotropy once the spherically symmetric spacetime configuration is assumed (Nashed & Hanafy 2022). However, for ò ≠ 0 (κ ≠ κ E ), a slight change in anisotropy is expected.…”

Section: The Modelmentioning

confidence: 98%

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Impact of Rastall Gravity on Mass, Radius, and Sound Speed of the Pulsar PSR J0740+6620

Hanafy

2022

ApJ

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Millisecond pulsars are perfect laboratories to test possible matter–geometry coupling and its physical implications in light of recent Neutron Star Interior Composition Explorer (NICER) observations. We apply Rastall field equations of gravity, where matter and geometry are nonminimally coupled, to Krori–Barua interior spacetime whereas the matter source is assumed to be anisotropic fluid. We show that all physical quantities inside the star can be expressed in terms of Rastall, ϵ, and compactness, C = 2GM/Rc 2, parameters. Using NICER and X-ray Multi-Mirror Newton X-ray-observational constraints on the mass and radius of the pulsar PSR J0740+6620, we determine the Rastall parameter to be at most ϵ = 0.041 in the positive range. The obtained solution provides a stable compact object; in addition the squared sound speed does not violate the conjectured sound speed c s 2 ≤ c 2 / 3 unlike the general relativistic treatment. We note that no equations of state are assumed; the model however fits well with linear patterns with bag constants. In general, for ϵ > 0, the theory predicts a slightly larger-size star in comparison to general relativity for the same mass. This has been explained as an additional force, due to matter–geometry coupling, in the hydrodynamic equilibrium equation, which contributes to partially diminishing the gravitational force effect. Consequently, we calculate the maximal compactness as allowed by the strong energy condition to be C = 0.735, which is ∼2% higher than general relativity prediction. Moreover, for the surface density at saturation nuclear density ρ nuc = 2.7 × 1014 g cm−3, we estimate the maximum mass M = 4M ⊙ at radius R = 16 km.

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Section: The Modelmentioning

confidence: 98%

“…This will be discussed in more details in Section 6. Notably, for ò < 0, the matter-geometry coupling turns the star to slightly smaller sizes in comparison with GR for the same mass (Nashed & Hanafy 2022); and therefore we omit this choice in the present work.…”

Section: Mass and Radius Observational Constraints From Psr J0740+6620mentioning

confidence: 99%

Impact of Rastall Gravity on Mass, Radius, and Sound Speed of the Pulsar PSR J0740+6620

Hanafy

2022

ApJ

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“…Remarkably, the matter-geometry coupling due to the trace T does not contribute to the anisotropy once the spherically symmetric spacetime configuration is assumed (Nashed & El Hanafy 2022). However, for α 1 ≠ 0 slight change in anisotropy is expected.…”

Section: The Linear Form Of F (R T) Modelmentioning

confidence: 95%

The Effect of f(R, T) Modified Gravity on the Mass and Radius of Pulsar HerX1

Nashed

2023

ApJ

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Millisecond pulsars are the perfect testable to examine potential matter-geometry coupling and its physical consequences in the context of the recent Neutron Star Interior Composition Explorer discoveries. We apply the field equations of modified gravity, f(R, T) = R + α T, to a spherically symmetric spacetime, where R is the Ricci scalar, α is a dimensional parameter, and T is the matter of the geometry. Five unknown functions are present in the output system of differential equations, which consists of three equations. To close the system, we make explicit assumptions about the anisotropy and the radial metric potential, g rr . We then solve the output differential equations and derive the explicit forms of the components of the energy-momentum tensor, i.e., density, radial, and tangential pressures. We look into the possibility that all of the physical parameters in the star can be reexpressed in terms of α and the compactness parameters, C = 2 GM Rc−2. We show that, for a given mass, the size permitted by Einstein’s general relativity is less due to the matter-geometry coupling in f(R, T). The validity of the hypothesis was validated by observations from an extra 21 pulsars. To achieve a surface density that is compatible with a neutron core at nuclear saturation density, the mass–radius curve enables masses up to 3.35M ⊙. We emphasize that although there is no assumption of an equation of state, the model fits well with a linear behavior. When comparing the surface densities of these 20 pulsars, we divided them into three groups. We show that these three groups are compatible with neutron cores.

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“…Equation (30) shows that the total mass of BH is function of r h , the charge and Λ ef f. . For specific value of the charge we plot the relation of the horizon mass-radius in Fig.…”

Section: The Thermodynamical Properties Of the Of Bh Given By Eq (19)mentioning

confidence: 99%

“…Moreover, external fields in the Lagrangian could give essentially the same behavior as Rastall's theory (for discussion of the external field see, for example [29]). An investigation of Rastall gravity, for an anisotropic star with a static spherical symmetry, has been discussed in [30]. The study of shadow and energy emission rates for a spherically symmetric non-commutative black hole in Rastall gravity has been carried out [31].…”

Section: Introductionmentioning

confidence: 99%

Nonlinear charged black hole solution in Rastall gravity

Nashed¹

2022

Preprint

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We show that the spherically symmetric black hole (BH) solution of a charged (linear case) field equation of Rastall gravitational theory is not affected by the Rastall parameter and this is consistent with the results presented in the literature. However, when we apply the field equation of Rastall's theory to a special form of nonlinear electrodynamics (NED) source, we derive a novel spherically symmetric BH solution that involves the Rastall parameter. The main source of the appearance of this parameter is the trace part of the NED source, which has a non-vanishing value, unlike the linear charged field equation. We show that the new BH solution is just Anti-de-Sitter Reissner-Nordström spacetime in which the Rastall parameter is absorbed into the cosmological constant. This solution coincides with Reissner-Nordström solution in the GR limit, i.e. when Rastall's parameter vanishing. To gain more insight into this BH, we study the stability using the deviation of geodesic equations to derive the stability condition. Moreover, we explain the thermodynamical properties of this BH and show that it is stable, unlike the linear charged case that has a second-order phase transition. Finally, we prove the validity of the first law of thermodynamics.

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Non-trivial class of anisotropic compact stellar model in Rastall gravity

Cited by 41 publications

References 124 publications

Impact of Rastall Gravity on Mass, Radius, and Sound Speed of the Pulsar PSR J0740+6620

Impact of Rastall Gravity on Mass, Radius, and Sound Speed of the Pulsar PSR J0740+6620

The Effect of f(R, T) Modified Gravity on the Mass and Radius of Pulsar HerX1

Nonlinear charged black hole solution in Rastall gravity

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