Relativistic Stars Research Articles

Stabilization of spherically symmetric static Boson stars by Coleman-Weinberg self-interaction potential

Our motivation in this work is due to the great importance of relativistic boson stars as fierce competitors of black holes. From theoretical perspective, they described by complex Klein Gordon (KG) scalar fields interacting with curved background in general form. In this work we use the Einstein-Klein Gordon (EKG) scalar tensor gravity in presence of the Coleman-Weinberg (CW) self-interaction potential to study formation of a spherically symmetric boson star and situation of its stability. We choose the CW potential because of its important role in description of cosmic inflation.

Physical viability of [formula omitted] gravity corrected charged anisotropic solutions

This article explores the impact of charge on the properties of relativistic compact star candidates exhibiting anisotropic distribution in f(Q) gravity, where Q represents a nonmetricity. A specific model of this gravitational theory is considered to simplify the system and establish the precise field equations that regulate the interaction between matter and geometry. Analysis of the static spherical symmetric structures is conducted by considering the non-singular feasible solutions. The Darmois constraints are used to determine the unknown constants in the metric coefficients. We explore different physical characteristics in the interior of charged compact stars to check their viability. Sound velocity and adiabatic index techniques are employed for stability state analysis. Proposed charged stars are determined to be both viable and stable in this theoretical framework.

Slowly rotating relativistic stars in [formula omitted] theory of gravity

In this paper, we investigate slowly rotating compact stars within the framework of f(R) gravity in a self-consistent way. We derive the equations describing the structure of compact stars in f(R) gravity and solve both the exterior and interior problems simultaneously. The study includes an equation of state. We considerably analyze the moment of inertia and its dependence on the stellar mass and the f(R) gravity. Future studies of the moment of inertia of compact stars may help determine the difference between f(R) gravity and general relativity, providing information on the high field domain of gravity. For our current analysis, we consider five different compact stars, namely, PSR1903+327, PSR1937+21, PSRJ1614−2230, CenX−3, and VelaX−1. To determine the viability of our model, we conduct a number of physical experiments, such as the analysis of energy density and pressure components, equilibrium and energy conditions, stability analysis, and the adiabatic index. The relationship between stellar objects’ mass, energy density, radius, and moment of inertia is observed. Our findings indicate that obtained results are physically adequate and consistent with the model we considered.

Noncomoving description of adiabatic radial perturbations of relativistic stars

Noncomoving description of adiabatic radial perturbations of relativistic stars

Adiabatic radial perturbations of relativistic stars: Analytic solutions to an old problem

Adiabatic radial perturbations of relativistic stars: Analytic solutions to an old problem

Strange star model in higher dimensions (D ≥ 4) with density-dependent B in pseudo-spheroidal geometry

In this paper, we have developed a class of new solutions for relativistic compact stars in higher-dimensional [Formula: see text] space-time assuming pseudo-spheroidal geometry of the [Formula: see text] metric component. To study the physical properties, we consider equation of state of interior strange matter [Formula: see text], as proposed in MIT bag model in the presence of a density-dependent [Formula: see text] parameter. The interior matter of a quark star may consist of three flavor quarks. We observe some interesting results. The parameter [Formula: see text] depends on the anisotropy [Formula: see text] in the interior, and at the stellar surface, [Formula: see text] attains a constant value independent of [Formula: see text]. At the interior, [Formula: see text] increases with the increase of [Formula: see text]. We also note that the value of B approaches a constant value with increasing spheroidal parameter [Formula: see text]. [Formula: see text] also depends on space-time dimensions and it is interesting to note that [Formula: see text] picks up negative values near core region which limits the number of space-time dimensions available for a stellar model. All the stability criterion and energy conditions hold good for a physically realistic stellar configuration. It is observed that strange quark matter may be stable or metastable or unstable depending upon the value of energy per baryon [Formula: see text]. Strange quark matter will be stable if energy per baryon [Formula: see text]. It is noted that the maximum mass obtainable in this model is [Formula: see text] considering stable strange quark matter when dimension [Formula: see text]. In addition, we observe that the dimensions have some effect on the gross properties of strange stars (SS).

Slowly rotating anisotropic relativistic stars

Slowly rotating anisotropic relativistic stars

Exact perfect fluid interior solutions and slowly rotating relativistic stars

Exact perfect fluid interior solutions and slowly rotating relativistic stars

Dynamical tidal response of nonrotating relativistic stars

Dynamical tidal response of nonrotating relativistic stars

The non-spherical ground state of Proca stars

Spherical Proca Stars (PSs) are regarded as the ground state amongst the family of PSs. In accordance, spherical PSs are thought to have a fundamental branch of stable solutions. In this Letter, we provide energetic, morphological and dynamical evidence that spherical PSs are actually excited states. The ground state is shown to be a family of static, non-spherical, in fact prolate, PSs. The spherical stars in the fundamental branch, albeit stable against spherical perturbations, turn out to succumb to non-spherical dynamics, undergoing an isometry breaking into prolate PSs. We also provide evidence for the dynamical formation of prolate PSs, starting from spherical dilute initial data, via gravitational cooling. Consequently, PSs provide a remarkable example of (possibly compact) relativistic stars, in General Relativity minimally coupled to a simple, physical, field theory model, where staticity plus stability implies non-sphericity.

Induced polar perturbations with stochastic effects in dense matter relativistic stars: A theoretical probe at intermediate sub-hydro mesoscopic scales

A linear response relation between metric and fluid perturbations driven by a background internal noise source is used as a framework for addressing stochastic effects in order to establish a mesoscopic theory for dense matter relativistic stars. In this paper, nonradial polar perturbations are worked out, which are important from the point of view of detection in future. We present qualitative first results in this paper, numerical estimates have to await further progress in theoretical modeling. These perturbations carry a new generalized stochastic nature and are obtained as solutions of the classical Einstein–Langevin equation which has been recently proposed. The significance of these stochastic nonradial polar perturbations lies at probing the intermediate sub-hydro scales inside the dense fluid. This formalism extends towards a mesoscopic scale nonequilibrium/near-equilibrium statistical mechanics study for relativistic star interiors. The generalized stochastic noise originates as the remnant of collapse mechanism and dynamical effects at intermediate scales in isolated massive stars which drives these polar perturbations. More specifically, for cold dense matter which is our focus in this paper, it is either the interplay between the degeneracy pressure and the gravitational pressure, or the multiscale phenomena like turbulences giving rise to the seeds of stochastic effects in the gravitating body. Characterizing such stochastic effects can lead to an improved understanding of the nature of dense matter and help to probe multiple scales which are yet untouched.

Compact stellar model with vanishing complexity under Vaidya–Tikekar background geometry

We make use of the condition of vanishing complexity, based on the current definition proposed by Herrera (Phys Rev D 97:044010, 2018), to find exact interior solutions to the Einstein equations for describing compact stellar objects. In the framework of general relativity, the complexity factor is an outcome of the orthogonal splitting of the Riemann tensor from which structure scalars are obtained. By using the Vaidya–Tikekar (V–T) metric ansatz (J Astrophys Astron 3:325, 1982) for the spacetime of a static spherically symmetric matter distribution, we model superdense, relativistic stars. The interior spacetime is matched to the exterior Schwarzschild solution across the boundary of the star where the radial pressure vanishes. The physical viability of the model has been tested following the current data corresponding to the pulsar 4U1820-30\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ 4U 1820-30 $$\\end{document}. The stability of the model fulfilled the given criteria, namely the Tolman–Oppenheimer–Volkoff equation, the adiabatic index and the causality conditions.

Impact of spacetime curvature on the physical behaviour of Vaidya and Tikekar (VT) type anisotropic compact objects

The Vaidya and Tikekar (1982) ansatz has so far provided numerous stellar solutions which are useful for the description of compact stars like neutron stars and quark stars. We re-examine the impacts of the spacetime curvature parameter of the Vaidya–Tikekar ansatz on the physical properties of the relativistic anisotropic star. For a spherically symmetric, static and anisotropic stellar configuration, in the Vaidya–Tikekar background spacetime, we develop new exact solutions by assuming a polytropic type equation of state pr=kρ1+1n−β. Recent data from observed pulsars are taken as input parameters to validate the developed model. We examine the impact of the spheroidal curvature parameter of the VT spacetime on the stellar behaviour and mass–radius (M–R) relationship. It is observed that with the increase in the departure from spherical geometry, values of physical quantities, such as density and pressure, increase.

Some new dark energy star models in Rastall gravity via Tolman–Kuchowicz potentials

In this paper, we are interested in modeling a new relativistic dark energy star by enforcing the static and anisotropic spherically symmetric fluid distribution in the realm of the Rastall theory of gravity. To do so, we have assumed a linear dark energy equation of state coupled with baryonic stellar matter: ρde=βρ, which has been used as a seed solution along with Tolman–Kuchowicz potentials to obtain the analytical solutions of the Rastall field equations. The stability of various physical attributes like matter variables, energy conditions, stability analysis, mass–radius relation, compactness and surface redshift have been examined corresponding to the observational data of the compact star PSRJ1614−2230 (R=9.69 km). Based on the evident results, for the small values of the Rastall parameter α, our proposed solutions are viable for a new stable relativistic dark energy star model in the realm of Rastall gravity, which comparatively seems to be more interesting than the results given in previous study (Saklany et al., 2022).

EVOLUTION OF THE X-RAY BINARY SYSTEM Sco X-1

The possible evolution of a bright low-mass X-ray binary system Sco X-1 is numerically investigated within the framework of a model assuming that the donor of the system (a satellite of a neutron star) fills its Roche lobe. The calculations take into account a strong induced stellar wind (ISW) of the donor, which occurs due to irradiation by hard radiation of an accreting relativistic star. At the same time, using the example of Sco X-1, three hypotheses are investigated, within the framework of which a high rate of mass exchange can be obtained for semi-separated X-ray binary stars. The first hypothesis is the presence of a strong ISW of the donor with standard magnetic braking. Calculations have shown that in this case it is possible to obtain a high rate of mass exchange, but at the same time the donor cannot fill the Roche lobe – it “goes under it”. The second hypothesis is an increase of magnetic braking, that is, an increase of the loss of angular momentum from the system due to the magnetic stellar wind of the donor (MSW). Such an amplification may be associated with the intense ISW of the donor in the presence of a strong magnetic field. Numerical modeling shows that with an increase of MSW by ~20 times, a high rate of mass exchange is possible when the donor fills the Roche lobe. The third hypothesis suggests the possibility of canceling the direct exchange of angular momentum between the orbital moment of the system and the moment of accreted matter passing from a low-mass donor to a more massive accretor. With such cancellation, the main process, increasing the semi-axis of the orbit, disappears. Calculations show that in this case it is possible to obtain a sufficiently high rate of mass exchange. However, the most likely reason for the increase of the rate of mass exchange in low-mass X-ray binary systems is probably the increase of magnetic braking.

Stellar structure modeling in Ricci-inverse gravity with Tolman–Kuchowicz spacetime

The primary objective of this research is to conduct an extensive investigation of stellar compact structures within the frame of the newly proposed Ricci-Inverse theory of gravity. The study utilizes the Tolman–Kuchowicz spacetime to explore these relativistic stars. In this work, we derive the modified field equations for a spherically symmetric line element with an isotropic matter distribution. To ensure physical validity, we consider appropriate expressions for the metric potentials i.e., ɛ=Br2+2ln(X) and ϑ=ln(1+ar2+br4). In order to determine the unknown parameters, we employ observational evidence from star models such as 4U1538−52, LMCX−4, EXO1785−248, 4U1820−30, and VelaX−1. Next, we examine and discuss the graphical behavior of several key parameters, including energy density and pressure, adiabatic index, equation of state, redshift function, and stability analysis. The observed behavior of these attributes aligns with accepted physical properties, and the emerging outcomes fall within the observed range. This demonstrates the viability of our proposed Ricci-Inverse gravity model.

Magnetic equilibria of relativistic axisymmetric stars: The impact of flow constants

Magnetic equilibria of relativistic axisymmetric stars: The impact of flow constants

Correction to: Formalism for stochastic perturbations and analysis in relativistic stars

Correction to: Formalism for stochastic perturbations and analysis in relativistic stars

On the Earth’s Electric Field Components Spectrally Localized at the Gravitational Waves of the Relativistic Binary Star Systems

On the Earth’s Electric Field Components Spectrally Localized at the Gravitational Waves of the Relativistic Binary Star Systems

Compact stars with dark energy in general relativity and modified gravity

We investigate realistic models of compact objects, focusing on neutron and strange stars, composed by dense matter and dark energy in the form of a simple fluid or scalar field interacting with matter. For the dark energy component, we use equations of state compatible with cosmological observations. This requirement strongly constrains possible deviations from the simple Λ-Cold Dark-Matter model with EoS pd=−ρd at least for small densities of the dark component. But we can propose that the density of dark energy interacting with matter can reach large values in relativistic stars and affects the star parameters such as the mass and radius. Simple models of dark energy are considered. Then we investigated possible effects from modified gravity choosing to study the R2 model combined with dark energy. Finally, the case of dark energy as scalar field non-minimally interacting with gravity is considered.