Analytical Stellar Models of Neutron Stars in f (T) Gravity (original) (raw)
Related papers
Analytical Stellar Models of Neutron Stars in Teleparallel Gravity
2021
In this paper, we developed three analytical models and obtained a new class of solutions describing compact stellar structures using the theory of teleparallel gravity. We consider the general anisotropic nature of stellar configurations and solve teleparallel gravity equations. In order to thoroughly analyze the various parameters of the stars, we developed three models by choosing various physically acceptable forms of metric potential e and radial pressure pr(r). We also analyze the impact of teleparallel gravity’s parameters β and β1 on the description of the stellar structures. We calculated model parameters such that models describing various observed neutron stars obey all physical conditions to be potentially stable and causal. By analyzing the impact of various parameters of teleparallel gravity on the description of anisotropic stellar structures, we found that three models developed in this paper can describe anisotropic neutron stars ranging from low density to high den...
Anisotropic compact stars in f(R) gravity
The European Physical Journal C, 2021
We derive a new interior solution for stellar compact objects in f\mathcal {(R)}f(R)gravityassumingadifferentialrelationtoconstraintheRiccicurvaturescalar.Tothisaim,weconsiderspecificformsfortheradialcomponentofthemetricandthefirstderivativeoff ( R ) gravity assuming a differential relation to constrain the Ricci curvature scalar. To this aim, we consider specific forms for the radial component of the metric and the first derivative off(R)gravityassumingadifferentialrelationtoconstraintheRiccicurvaturescalar.Tothisaim,weconsiderspecificformsfortheradialcomponentofthemetricandthefirstderivativeoff\mathcal {(R)}f(R).After,thetimecomponentofthemetricpotentialandtheformoff ( R ) . After, the time component of the metric potential and the form off(R).After,thetimecomponentofthemetricpotentialandtheformoff({\mathcal {R}})f(R)functionarederived.Fromtheseresults,itispossibletoobtaintheradialandtangentialcomponentsofpressureandthedensity.Theresultinginteriorsolutionrepresentsaphysicallymotivatedanisotropicneutronstarmodel.Itispossibletomatchitwithaboundaryexteriorsolution.Fromthismatching,thecomponentsofmetricpotentialscanberewrittenintermsofacompactnessparameterCwhichhastobef ( R ) function are derived. From these results, it is possible to obtain the radial and tangential components of pressure and the density. The resulting interior solution represents a physically motivated anisotropic neutron star model. It is possible to match it with a boundary exterior solution. From this matching, the components of metric potentials can be rewritten in terms of a compactness parameter C which has to bef(R)functionarederived.Fromtheseresults,itispossibletoobtaintheradialandtangentialcomponentsofpressureandthedensity.Theresultinginteriorsolutionrepresentsaphysicallymotivatedanisotropicneutronstarmodel.Itispossibletomatchitwithaboundaryexteriorsolution.Fromthismatching,thecomponentsofmetricpotentialscanberewrittenintermsofacompactnessparameterCwhichhastobeC=2GM/Rc^2<<0.5$$ C = 2 G M / R c 2 < < 0.5 for physical consistency. Other physical conditions for real stellar objects are taken into account according t...
Further stable neutron star models from f ( R ) gravity
Journal of Cosmology and Astroparticle Physics, 2013
Neutron star models in perturbative f (R) gravity are considered with realistic equations of state. In particular, we consider the FPS, SLy and other equations of state and a case of piecewise equation of state for stars with quark cores. The mass-radius relations for f (R) = R + R(e −R/R 0 − 1) model and for R 2 models with logarithmic and cubic corrections are obtained. In the case of R 2 gravity with cubic corrections, we obtain that at high central densities (ρ > 10ρns, where ρns = 2.7 × 10 14 g/cm 3 is the nuclear saturation density), stable star configurations exist. The minimal radius of such stars is close to 9 km with maximal mass ∼ 1.9M⊙ (SLy equation). A similar situation takes place for AP4 and BSK20 EoS. Such an effect can give rise to more compact stars than in General Relativity. If observationally identified, such objects could constitute a formidable signature for modified gravity at astrophysical level. Another interesting result can be achieved in modified gravity with only a cubic correction. For some EoS, the upper limit of neutron star mass increases and therefore these EoS can describe realistic star configurations (although, in General Relativity, these EoS are excluded by observational constraints).
Anisotropic compact stars in f(T) gravity
Astrophysics and Space Science, 2015
This paper deals with the theoretical modeling of anisotropic compact stars in the framework of f (T) theory of gravity, where T is torsion scalar. To this end, we have used the exact solutions of Krori and Barua metric to a static spherically symmetric metric. The unknown constants involved in the Krori and Barua metric have been specified by using the masses and radii of compact stars 4U 1820-30, Her X-1, SAX J 1808-3658. The physical properties of these stars have been analyzed in the framework of f (T) theory. In this setting, we have checked the anisotropic behavior, regularity conditions, stability and surface redshift of the compact stars.
Anisotropic neutron stars by gravitational decoupling
The European Physical Journal C, 2019
In this work we obtain an anisotropic neutron star solution by gravitational decoupling starting from a perfect fluid configuration which has been used to model the compact object PSR J0348+0432. Additionally, we consider the same solution to model the Binary Pulsar SAX J1808.4-3658 and X-ray Binaries Her X-1 and Cen X-3 ones. We study the acceptability conditions and obtain that the MGD-deformed solution obey the same physical requirements as its isotropic counterpart. Finally, we conclude that the most stable solutions, according to the adiabatic index and gravitational cracking criterion, are those with the smallest compactness parameters, namely SAX J1808.4-3658 and Her X-1.
Journal of Cosmology and Astroparticle Physics
In this work we investigate neutron stars (NS) in f (R, T) gravity for the case R + 2λT , R is the Ricci scalar and T the trace of the energy-momentum tensor. The hydrostatic equilibrium equations are solved considering realistic equations of state (EsoS). The NS masses and radii obtained are subject to a joint constrain from massive pulsars and the event GW170817. The parameter λ needs to be negative as in previous NS studies, however we found a minimum value for it. The value should be |λ| 0.02 and the reason for so small value in comparison with previous ones obtained with simpler EsoS is due to the existence of the NS crust. The pressure in theory of gravity depends on the inverse of the sound velocity v s. Since, v s is low in the crust, |λ| need to be very small. We found that the increment in the star mass is less than 1%, much smaller than previous ones obtained not considering the realistic stellar structure, and the star radius cannot become larger, its changes compared to GR is less than 3.6% in all cases. The finding that using several relativistic and non-relativistic models the variation on the NS mass and radius are almost the same for all the EsoS, manifests that our results are insensitive to the high density part of the EsoS. It confirms that stellar mass and radii changes depend only on crust, where the EoS is essentially the same for all the models. The NS crust effect implying very small values of |λ| does not depend on the theory's function chosen, since for any other one the hydrostatic equilibrium equation would always have the dependence 1/v s. Finally, we highlight that our results indicate that conclusions obtained from NS studies done in modified theories of gravity without using realistic EsoS that describe correctly the NS interior can be unreliable.
Neutron Stars : A Comparative Study
arXiv: General Relativity and Quantum Cosmology, 2015
The inner structure of neutron star is considered from theoretical point of view and is compared with the observed data. We have proposed a form of an equation of state relating pressure with matter density which indicates the stiff equation of state of neutron stars. From our study we have calculated mass(M), compactness(u) and surface red-shift(Zs ) for the neutron stars namely PSR J1614-2230, PSR J1903+327, Cen X-3, SMC X-1, Vela X-1, Her X-1 and compared with the recent observational data. We have also indicated the possible radii of the different stars which needs further study. Finally we have examined the stability for such type of theoretical structure.
Structure of neutron stars in R-squared gravity
The effects implied for the structure of compact objects by the modification of General Relativity (GR) produced by the generalization of the Lagrangian density to the form f (R) = R+αR2,where R is the Ricci curvature scalar, have been recently explored. It seems likely that this squared-gravity may allow heavier Neutron Stars (NSs) than GR. In addition, these objects can be useful to constrain free parameters of modified-gravity theories. The differences between alternative gravity theories are enhanced in the strong gravitational regime. In this regime, because of the complexity of the field equations, perturbativemethods become a good choice to treat the problem. Following previous works in the field, we performed a numerical integration of the structure equations that describe NSs in f (R)-gravity, recovering their mass-radius relations, but focusing on particular features that arise from this approach in the profiles of the NS interior.We show that these profiles run in correlation with the second-order derivative of the analytic approximation to the Equation of State (EoS), which leads to regions where the enclosed mass decreases with the radius in a counter-intuitive way. We reproduce all computations with a simple polytropic EoS to separate zeroth-order modified gravity effects.
Neutron stars: compact objects with relativistic gravity
TURKISH JOURNAL OF PHYSICS, 2016
General properties of neutron stars are briefly reviewed with an emphasis on the indispensability of general relativity in our understanding of these fascinating objects. In Newtonian gravity the pressure within a star merely plays the role of opposing self-gravity. In general relativity all sources of energy and momentum contribute to the gravity. As a result the pressure not only opposes gravity but also enhances it. The latter role of pressure becomes more pronounced with increasing compactness, M/R where M and R are the mass and radius of the star, and sets a critical mass beyond which collapse is inevitable. This critical mass has no Newtonian analogue; it is conceptually different than the Stoner-Landau-Chandrasekhar limit in Newtonian gravity which is attained asymptotically for ultrarelativistic fermions. For white dwarfs the general relativistic critical mass is very close to the Stoner-Landau-Chandrasekhar limit. For neutron stars the maximum mass-so called Oppenheimer-Volkoff limit-is significantly smaller than the Stoner-Landau-Chandrasekhar limit. This follows from the fact that the general relativistic correction to hydrostatic equilibrium within a neutron star is significant throughout the star, including the central part where the mass contained within radial coordinate, m(r), and the Newtonian gravitational acceleration, Gm(r)/r 2 , are small.
The European Physical Journal Plus
The solutions for the Tolmann-Oppenheimer-Volkoff (TOV) equation bring valuable informations about the macroscopical features of compact astrophysical objects as neutron stars. They are sensitive to both the equation of state considered for nuclear matter and the background gravitational theory. In this work we construct the TOV equation for a conservative version of the f (R, T) gravity. While the non-vanishing of the covariant derivative of the f (R, T) energy-momentum tensor yields, in a cosmological perspective, the prediction of creation of matter throughout the universe evolution as shown by T. Harko, in the analysis of the hydrostatic equilibrium of compact astrophysical objects, this property still lacks a convincing physical explanation. The imposition of ∇ µ Tµν = 0 demands a particular form for the function h(T) in f (R, T) = R + h(T), which is here derived. Therefore, the choice of a specific equation of state for the star matter demands a unique form of h(T), manifesting a strong connection between conserved f (R, T) gravity and the star matter constitution. We construct and solve the TOV equation for the general equation of state for p = kρ Γ , with k being the EoS parameter, ρ the energy density and Γ is the adiabatic index. We also derive the macroscopical properties of neutron stars (Γ = 5/3) within this approach.