Exploring structure and stability of charged gravastar in non-conservative theory of gravity

The ([formula omitted])-dimensional gravastars

In this paper, we have constructed a unique gravastar model proposed by Mazur and Mottola in the spherically symmetric stellar system under the mimetic gravitational framework with the presence of isotropic fluid source. The gravastar consists of three regions namely the interior, the shell and the exterior. In the interior region, the gravastar follows the equation of state(EoS) p = −ρ. Here we have found the non-singular solutions. The next region is a thin shell of ultra-relativistic stiff fluid having EoS p = ρ in which we have investigated several physical properties such as the proper length, energy and entropy and it is observed that all these properties are increasing with the increase in thickness of the shell. The exterior of the gravastar has been described as the Schwarzschild type. We found the matching between the surfaces of interior and exterior of the gravastar. Using the junction conditions, we have obtained the surface energy density and surface pressure which are found to be decreasing with the thickness of the shell. Moreover our gravastar model is found to be stable as we observe from the speed of sound and the entropy maximization technique. Our derived model is in accordance with the works also. Finally we have developed a stable gravastar model without singularities and devoid of any incompleteness in classical black hole theory.

New gravastar model in generalised cylindrically symmetric space–time and prediction of mass limit

The gravastar (or the Gravitational Vacuum Star) is a very serious alternative proposed to the principle of the black hole, the model of which was originally developed by Mazur and Mottola. A gravastar is an astronomically hypothetically condensed object which is a gravitationally dark vacuum star or a gravitational vacuum condensate star, which is singularity free, spherically symmetric and also super compact. This study concerns about the model of the gravastar in the modified [Formula: see text] gravity considering the form [Formula: see text]. From Mazur–Mottola [P. O. Mazur and E. Mottola, Universe 9, 88 (2023); P. O. Mazur and E. Mottola, Proc. Natl. Acad. Sci. 101, 9545 (2004)], we get to know that a gravastar model has three distinct regions having various Equations of State (EoS). We have inquired into the interior portion with the spacetime considering [Formula: see text], for the dark sector of the interior region, here the negative matter-energy density exerting a repulsive force on the immediate thin shell with the EoS [Formula: see text] where it is considered as an ultra-relativistic fluid. We have studied the properties such as energy density, proper length, total energy and entropy. Next comes the vacuum exterior region of the gravastar which is being described by the Schwarzschild-de-Sitter solution. Also from Darmois–Israel formalism, we have probed the junction connecting the inner and the outer surfaces of the gravastar.

This paper discusses the configuration of gravitational vacuum star or gravastar with the impact of geometry and matter coupling present in $f(R,T)$ gravity. The gravastar is also conceptualized as a substitute for a black hole which is illustrated by three geometries known as (1) the interior geometry, (2) the intermediate thin-shell and (3) the exterior geometry. For a particular $f(R,T)$ model, we analyze these geometries corresponding to Kuchowicz metric function. We evaluate another metric potential for the interior domain as well as the intermediate shell which is non-singular for both domains. The Schwarzschild metric is adopted to demonstrate the exterior geometry of gravastar, while the numerical values of unknown constants are calculated through boundary conditions. Finally, we discuss different features of gravastar regions like proper length, energy, surface redshift as well as equation of state parameter. We conclude that the gravastar model can be regarded as a successful replacement of the black hole in the context of this gravity.

We propose a class of models, in which stable gravastar with large surface redshift becomes a solution. In recent decades, gravastars have become a plausible substitute for black holes. Researchers have explored stable gravastar models in various alternative gravity theories, in addition to the conventional framework of general relativity. In this paper, we present a stellar model within the framework of Einstein's gravity with two scalar fields, in accordance with the conjecture proposed by Mazur and Mottola [Proc. Nat. Acad. Sci. 101 (2004), 9545-9550]. In the model, the two scalar fields do not propagate by imposing constraints in order to avoid ghosts. The gravastar comprises two distinct regions, namely: (a) the interior region and (b) the exterior region. We assume the interior region consists of the de Sitter spacetime, and the exterior region is the Schwarzschild one. The two regions are connected with each other by the shell region. On the shell, we assume that the metric is given by a polynomial function of the radial coordinate r. The function has six constants. These constants are fixed by the smooth junction conditions, i.e., the interior region with the interior layer of the shell and the exterior region with the exterior layer of the shell. From these boundary conditions, we are able to write the coefficients of the scalar fields in terms of the interior radius and exterior radius. To clarify the philosophy of this study, we also give two examples of spacetimes that asymptote as the de Sitter spacetime for small r and as the Schwarzschild spacetime for large r. Exploration is focused on the physical attribute of the shell region, specifically, its proper length. The gravastar model's stability has frequently been examined by analyzing the relationship between surface redshift and shell thickness, a comparison we also undertake with previous models. Especially, we show that there exists a stable gravastar with a large surface redshift prohibited by the instability in the previous works. Furthermore, by checking the effective equation of state parameters, we show that the gravastar geometry realized in this paper by using two scalar fields could be difficult to generate with ordinary fluid.

Charged gravastar model in Rastall theory of gravity

Study of gravastars admitting conformal motion in [formula omitted] gravity

In the last few decades, gravastars have been proposed as an alternative to black holes. The stability of a gravastar has been examined in many modified theories of gravity along with Einstein's GR. The gravity, a successfully modified theory of gravity for describing the current accelerated expansion of the universe, has been used in this study to examine gravastar in different aspects. According to Mazur and Mottola [Proc. Natl. Acad. Sci. 101, 9545 (2004); Gravitational condensate stars: An alternative to black holes, I12-011, (2002)], a gravastar has three regions with three different equations of state. In this study, we examined the interior of a gravastar by considering EoS to describe the dark sector for the interior region. The next region is a thin shell of ultrarelativistic stiff fluid, in which we investigated several physical properties, including proper length, energy, entropy, and surface energy density. Additionally, we examined the surface redshift and speed of sound to check the potential stability of our proposed thin-shell gravastar model. Furthermore, we used the entropy maximization technique to verify the stability of the gravastar model. A gravastar's outer region is a complete vacuum described by exterior Schwarzschild geometry. Finally, we presented a stable gravastar model, which is singularity-free and devoid of any incompleteness in classical black hole theory.

Study of gravastar admitting Tolman IV spacetime in Rastall theory

This paper examines the structure of gravastar (gravitationally vacuum star) in the background of [Formula: see text] theory. The gravastar can be regarded as a substitute for a black hole comprising of three regions (i) the interior domain, (ii) the intrinsic shell and (iii) the exterior domain. We investigate these domains by employing Karmarkar’s condition by assuming a specific [Formula: see text] model. The field equations are solved to evaluate nonsingular solutions of both the interior and intermediate regions. Inner as well as outer spacetimes are matched together using Israel formalism to obtain density and pressure at the joining surface. Different attributes of gravastar like the equation of state parameter, proper length, entropy and energy are analyzed through graphical behavior. It is found that the gravastar model is a viable alternative to the black hole in the context of this gravity.

This paper studies the influence of charge on a compact stellar structure also regarded as vacuum condensate star in the background of [Formula: see text] gravity. This object is considered the alternate of black hole whose structure involves three distinct regions, i.e. interior, exterior and thin-shell. We analyze these domains of a gravastar for a particular model of this modified theory. In the inner region of a gravastar, the considered equation of state defines that energy density is equal to negative pressure which is the cause of repulsive force on the spherical shell. In the intermediate shell, pressure and energy density are equal and contain ultra-relativistic fluid. The inward-directed gravitational pull of thin-shell counterbalances the force exerted by the inner region of a gravastar allowing the formation of a singularity-free object. The Reissner–Nordström metric presents the outer vacuum spherical domain. Moreover, we discuss the impact of the charge on physical attributes of a gravastar such as the equation of state parameter, entropy, proper length and energy. We conclude that singularity-free solutions of charged gravastar are physically consistent in this modified theory.

This paper investigates the geometry of a gravitational vacuum star (also known as a gravastar) from the perspective of f(R,T2) gravity. The gravastar can be treated as a black hole substitute with three domains: (i) the inner domain, (ii) the intrinsic shell, and (iii) the outer domain. We examine these geometries using Kuchowicz ansatz for temporal metric function corresponding to a specific f(R,T2) model. We compute a nonsingular radial metric potential for both the interior and intermediate domains. The matching of these domains with exterior Schwarzschild vacuum results in boundary conditions that assist in the evaluation of unknown constants. Finally, we examine various attributes of gravastar domains, such as the equation of state parameter, proper length, energy, and surface redshift. We conclude that the gravastar model is a viable alternative to the black hole in the background of this gravity.

This study investigates three distinct charged gravastar models within the framework of fT modified gravity, considering the functional forms fT=T, fT=a+bT, and fT=T2. Inspired by the Mazur–Mottola conjecture, we propose these models as singularity-free alternatives to black holes, each characterized by a three-region structure: (i) an interior de Sitter core, (ii) an intermediate thin shell composed of ultrarelativistic matter, and (iii) an exterior region described by the Reisner Nordstrom solution and other novel spherically symmetric vacuum solutions. We derive a complete set of exact, singularity-free solutions for the charged gravastar configuration, demonstrating their mathematical consistency and physical viability in the context of alternative gravity theories. Notably, the field equations governing the thin shell are solved using an innovative approach based on Killing vector symmetries, eliminating the need for approximations commonly employed in prior studies. Furthermore, we analyze key physical properties of the thin shell, including its proper length, entropy distribution, and energy content. A thorough examination of the energy conditions reveals the thermodynamic stability and viability of these models. Our results contribute to the growing body of work on exotic compact objects and provide new insights into the interplay between modified gravity, electromagnetism, and non-singular black hole alternatives.

Charged anisotropic fluid sphere in [formula omitted] gravity satisfying Vaidya - Tikekar metric