Gravitational Decoupling Research Articles

Analyzing the influence of geometrical deformation on photon sphere and shadow radius: A new analytical approach — Spherically symmetric spacetimes

In this paper, we introduce a new approach to study the behavior of the photon sphere and shadow radius. Our method uses extended gravitational decoupling and reveals two important analytic results. First, the additional matter field alters the photon sphere radius: it increases if g′(rph(0))>0 and decreases if g′(rph(0))<0 (where g′ represents the derivative of a specific metric function evaluated at the original photon sphere radius). Second, the presence of the matter field can modify the black hole shadow size. If grph(0)>0, the shadow shrinks, while it grows for grph(0)<0. These findings provide a deeper insight into how matter distribution influences the characteristics of black holes and their observable features. Through a systematic framework and various illustrative examples, our investigation not only clarifies these fundamental aspects but also significantly enhances the theoretical framework of black hole astrophysics.

Traversable wormholes in minimally geometrical deformed trace-free gravity using gravitational decoupling

In this work, we investigate wormhole solutions through the utilization of gravitational decoupling, employing the Minimal Geometric Deformation (MGD) procedure within the framework of Trace-Free Gravity. We base our investigation on static and spherically symmetric Morris-Thorne traversable wormholes, considering both constant and variable equation of state parameters. We derive the field equations and extract the shape function for each scenario. Moreover, we explore the gravitational decoupling technique and examine various forms of energy density for both a smeared and particle-like gravitational source, encompassing the realm of noncommutative geometry and a statically charged fluid. We also examinethe wormhole geometry through the utilization of embedding diagrams. Through our analysis, we uncover a violation of the Null Energy Condition (NEC). To conclude, we employ the Gauss-Bonnet theorem to determine the weak deflection angle for the wormhole configurations.

Complexity-free charged anisotropic Finch-Skea model satisfying Karmarkar condition

By making use of the extended geometric deformation (EGD) approach, this work explores the charged anisotropic Finch-Skea solution satisfying the Karmarkar condition. The implementation of EGD-approach splits the original gravitational source into perfect and anisotropic fluid configurations. We employ Herrera’s complexity factor Herrera L (2018 Phys. Rev. D 97 044010) formalism to develop theoretical models characterizing the role of complexity in the Finch-Skea solution. The use of the Karmarkar condition enables us to derive a solution for the isotropic, charged spherical configuration by defining a Finch-Skea metric that evaluates the deformation functions. The Finch-Skea ansatz serves as a valuable seed model for solving the seed-gravitational source, however, the zero-complexity constraint is employed to solve the remaining set of anisotropic equations. We match the interior metric manifold attributed to the spherically symmetric ansatz with the classical Reissner-Nordström metric. We examined the influence of gravitational decoupling on the anisotropic Finch-Skea solution. We also analyzed the physical viability of the presented results using graphical representations for the thermodynamic variables.

Thermodynamical analysis with extended phase transition of AdS hairy black hole in gravitational decoupling theory

This article explores various thermodynamical aspects and the extended phase space of the AdS hairy black hole within the context of gravitational decoupling. This study focused on thermodynamic properties such as geometrical mass, Hawking temperature, entropy, specific heat, Gibbs free energy (both locally and globally) and P-V criticality at the horizon radius. The thermodynamic stability of the AdS hairy black hole has been established based on its positive heat capacity. The analysis of Gibbs free energy is utilized to investigate the behavior of the first-order phase transition. Thermodynamic pressure, denoted by P, is related to the cosmological constant by the formula P=−Λ8π . In addition, a numerical investigation has been carried out to examine the equation of the state parameter and its critical values.

No Cauchy horizon in a gravitational decoupled Reissner–Nordström spacetime

In this article, using gravitational decoupling by means of the extended geometric deformation approach, we obtain a new hairy spherically symmetric and asymptotically flat charged black hole solution starting from the well known Reissner–Nordström manifold. The resulting spacetime, is characterized by a spacelike singularity at r=0, which is protected by an event horizon rH, where the original Cauchy horizon of the seed manifold is deleted, and no additional causal structure and physical singularities are introduced by the mechanism. To avoid this particular surface, the magnitude of the primary hair introduced by the scheme, is constrained in order to violate the strong energy condition in the black hole region r<rH.

The fermionic greybody factor and quasinormal modes of hairy black holes, as well as Hawking radiation’s power spectrum and sparsity

A hairy black hole (HBH) emerges due to matter surrounding the Schwarzschild metric when using the Extended Gravitational Decoupling (GD) approach. The fermionic greybody factors (GFs) and quasinormal modes (QNMs) as well as Hawking spectra and sparsity of HBH solutions are investigated. We consider massive and massless spin-1/2 fermions, along with massless spin-3/2 fermions. The equations of the effective potential for fermions with different spins are derived in HBH spacetime. Then, the rigorous bound method is used to calculate the fermionic spin-1/2 and spin-3/2 GFs. With the time domain integration method at our disposal, we illustrate the impact of additional parameters on the ringdown waveform of the massless fermionic spin-1/2 and spin-3/2 fields and, in turn, on their quasinormal modes. We then delve into investigating the Hawking spectra and sparsity of the radiation emitted by an HBH. Hairy parameters significantly affect the sparsity of Hawking radiation as well. We observe that the total power emitted by the BH increases both with α\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\alpha $$\\end{document} and Q but decreases with l0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$l_{0}$$\\end{document}. Our study conclusively shows the significant impact of the additional parameters on important astrophysical phenomena such as quasinormal modes, Hawking spectra, and sparsity.

Decoupled anisotropic Buchdahl’s relativistic models in f( R,T ) theory

This paper constructs three different anisotropic extensions of the existing isotropic solution to the modified field equations through the gravitational decoupling in f(R,T) theory. For this, we take a static sphere that is initially filled with the isotropic fluid and then add a new gravitational source producing anisotropy in the system. The field equations now correspond to the total matter configuration. We transform the radial metric component to split these equations into two sets characterizing their parent sources. The unknowns comprising in the first set are determined by considering the Buchdahl isotropic solution. On the other hand, we employ different constraints related to the additional gravitational source and make the second system solvable. Further, the constant triplet in Buchdahl solution is calculated by means of matching criteria between the interior and exterior geometries at the spherical boundary. The mass and radius of a compact star LMC X-4 are used to analyze the physical relevancy of the developed models. We conclude that our resulting models II and III are in well-agreement with acceptability conditions for the considered values of the parameters.

Anisotropic extensions of Tolman IV through decoupling in energy–momentum squared gravity

This paper is dedicated to the precise computation of anisotropic extensions for the Tolman IV solution. These extensions are achieved through the utilization of the extended gravitational decoupling scheme within the framework of [Formula: see text] gravity, where R is the Ricci scalar and [Formula: see text] is the contraction of energy–momentum tensor. In this context, we select a linear model characterized by the expression [Formula: see text], where the parameter [Formula: see text] establishes a connection between the geometric and matter components. The extended gravitational decoupling technique incorporates a decoupling parameter that governs the extent of the induced anisotropy. Deformations in the radial and temporal metric components lead to the decomposition of the field equations into two distinct subsystems. One of these sets pertains to the isotropic solution, while the other is addressed by implementing the extra constraints. We examine the outcomes through graphical analysis and investigate the viability and stability of the obtained anisotropic solutions for the celestial object. Moreover, we study the mass, compactness and surface redshift of the system to gain a comprehensive understanding of its characteristics. It is concluded that this technique in this modified gravity yields physically acceptable solutions.

Gravitationally decoupled charged anisotropic solutions in Rastall gravity

This paper develops the stellar interior geometry for charged anisotropic spherical matter distribution by developing an exact solution of the field equations of Rastall gravity using the notion of gravitational decoupling. The main purpose of this investigation is the extension of the well-known isotropic model within the context of charged isotropic Rastall gravity solutions. The second aim of this work is to apply gravitational decoupling via a minimal geometric deformation scheme in Rastall gravity. Finally, the third one is to derive an anisotropic version of the charged isotropic model previously obtained by applying gravitational decoupling technology. We construct the field equations which are divided into two sets by employing the geometric deformation in radial metric function. The first set corresponds to the seed (charged isotropic) source, while the other one relates the deformation function with an extra source. We choose a known isotropic solution for spherical matter configuration including electromagnetic effects and extend it to an anisotropic model by finding the solution of the field equations associated with a new source. We construct two anisotropic models by adopting some physical constraints on the additional source. To evaluate the unknown constants, we use the matching of interior and exterior spacetimes. We investigate the physical feasibility of the constructed charged anisotropic solutions by the graphical analysis of the metric functions, density, pressure, anisotropy parameter, energy conditions, stability criterion, mass function, compactness, and redshift parameters. For the considered choice of parameters, it is concluded that the developed solutions are physically acceptable as all the physical aspects are well-behaved.

Anisotropic extension of Kohler–Chao–Tikekar solution by minimal geometric deformation

This work is devoted to transforming the known cosmological solution of Kohler–Chao–Tikekar into an anisotropic interior solution using the framework of Gravitational Decoupling by minimal geometric deformation. The resulting interior solution fulfils the fundamental physical acceptability stellar conditions for a specific set of compactness factors. The stability of the model is also investigated.

A four parameters quark star in quadratic [formula omitted]action

In this collaborative work, we model charged compact objects within the framework of f(Q) gravity. We assume a quadratic form for the metricity function cast as f(Q)=Q+aQ2 where a can be thought of as a ‘switch’, regaining the classical general relativity limit when it vanishes. In order to close the system of governing equations, we adopt the Krori–Barua ansatz for the metric functions and the MIT bag model equation of state (EOS) determines the evolution of the electric field. The resulting models are singularity-free and describe physically realizable stellar structures such as neutron stars. We demonstrate that the physical attributes of our models are sensitive to four parameters, namely, the EOS, metricity, and charge parameters together with the bag constant. We observe that an increase in the quadratic contribution culminates in a decrease of the density, radial pressure, electric field, and sound speeds while ωr,ωt, anisotropy, and pt increase. The novelty in our work centers on a possible mechanism of increasing the anisotropy of the stellar interior without resorting to exotic fluids or anisotropisation via gravitational decoupling. The robustness of our models can account for observed mass–radius relations of well-known compact stars such as PSR J1614-2230, PSR J1903+6620, Cen X-3 and LMC X-4 and the secondary component of GW190814 event.

The Effect of Gravitational Decoupling on Constraining the Mass and Radius for the Secondary Component of GW190814 and Other Self-bound Strange Stars in f(Q) Gravity Theory

Inspired by the conundrum of the gravitational event GW190814, which brings to light the coalescence of a 23 M ⊙ black hole with a yet-to-be-determined secondary component, we look to modeling compact objects within the framework of gravity by employing the method of gravitational decoupling. We impose a quadratic equation of state (EOS) for the interior matter distribution, which in the appropriate limit reduces to the MIT bag model. The governing field equations arising from gravitational decoupling bifurcate into the and sectors, leading to two distinct classes of solutions. Both families of solutions are subjected to rigorous tests, qualifying them to describe a plethora of compact objects, including neutron stars, strange stars, and the possible progenitor of the secondary component of GW190814. Using observational data of mass–radius relations for compact objects LMC X-4, Cen X-3, PSR J1614–2230, and PSR J0740+6620, we show that it is possible to generate stellar masses and radii beyond 2.0 M ⊙ for neutron stars. Our findings reveal that the most suitable and versatile model in this framework is the quadratic EOS, which accounts for a range of low-mass stars and typical stellar candidates describing the secondary component of GW190814.

Gravitational decoupling of anisotropic stars in the Brans–Dicke theory

Anisotropic spherically symmetric solutions within the framework of the Brans–Dicke theory are uncovered through a unique gravitational decoupling approach involving a minimal geometric transformation. This transformation effectively divides the Einstein field equations into two separate systems, resulting in the alteration of the radial metric component. The first system encompasses the influence of the seed source, derived from the metric functions of the isotropic Tolman IV solution. Meanwhile, the anisotropic source is subjected to two specific constraints in order to address the second system. By employing matching conditions to determine the unknown constants at the boundary of the stellar object, a comprehensive examination of the internal structure of stellar systems ensues. This investigation delves into the impact of the decoupling parameter, the Brans–Dicke parameters, and a scalar field on the structural characteristics of anisotropic spherically symmetric spacetimes, all while considering the strong energy conditions.

Charged anisotropic compact stellar models under gravitational decoupling scheme

The aim of this paper is to obtain new physically admissible exact anisotropic stellar models via gravitational decoupling technique. This will be done by taking Korkina and Orlyanskii model solution as a seed solution and extend it to an anisotropic domain via gravitational decoupling through the minimal geometric deformation (MGD) approach. We analyze the physical properties of four compact star models Her [Formula: see text] (Mass [Formula: see text], [Formula: see text][Formula: see text]km), LMC [Formula: see text] ([Formula: see text], [Formula: see text][Formula: see text]km), PSR [Formula: see text] ([Formula: see text], [Formula: see text][Formula: see text]km) and PSR [Formula: see text] ([Formula: see text], [Formula: see text][Formula: see text]km). We demonstrate the stability conditions of the obtained solution by plotting energy conditions, velocity of sound, adiabatic index and all the thermodynamic parameters and equilibrium conditions via TOV equation, etc. We found that the results are physically well behaved and also fulfill the requirement of stability criteria inside the anisotropic fluid sphere. We study the physical features of the solutions in detail, analytically and graphically for the four compact stars Her [Formula: see text], LMC [Formula: see text], PSR [Formula: see text] and PSR [Formula: see text]. Based on the results we realized that the extended gravitational decoupling technique is very effective for the analysis of the interior of the compact stellar structures.

Minimally deformed anisotropic stars in dark matter halos under EGB-action

In this paper, we introduce an anisotropic model using a dark matter (DM) density profile in Einstein–Gauss–Bonnet (EGB) gravity using a gravitational decoupling method introduced by Ovalle (Phys Rev D 95:104019, 2017), which has provided an innovative approach for obtaining solutions to the EGB field equations for the spherically symmetric structure of stellar bodies. The Tolman and Finch–Skea (TFS) solutions of two metric potentials, g_{tt} and g_{rr}, have been used to construct the seed solution. Additionally, the presence of DM in DM halos distorts spacetime, causing perturbations in the g_{rr} metric potential, where the quantity of DM is determined by the decoupling parameter beta . The physical validity of the solution, along with stability and equilibrium analysis, has also been performed. Along with stability and equilibrium analysis, the solution’s physical validity has also been examined. Additionally, we have shown how both constants affect the physical characteristics of the solution. Using a M{-}R diagram, it has been described how the DM component and the GB constant affect the maximum permissible masses and their corresponding radii for various compact objects. Our model predicts the masses beyond the 2~M_{odot } and maximum radii 11.92^{+0.02}_{-0.01} and 12.83^{+0.01}_{-0.02} for larger value of alpha under density order 10^{15}~text {g}/text {cm}^3 and 10^{14}~text {g}/text {cm}^3, respectively, while the radii become 11.96^{+0.01}_{-0.01} and 12.81^{+0.01}_{-0.02} for larger value of beta .

Charge effect on isotropization and complexity of extended decoupled anisotropic stellar models

The objective of this paper is to construct some possible extensions of the existing anisotropic compact interiors to the Einstein–Maxwell framework by utilizing the extended gravitational decoupling. For this purpose, a static sphere initially coupled with the anisotropic distribution is assumed, and we call it the original source. We then extend this configuration by adding another gravitational matter source whose impact on the considered geometry is commanded by the decoupling parameter. We establish the field equations representing the total matter source which are partitioned into two distinct systems after implementing transformations on both radial/temporal metric functions. These two sets describe the seed and additional sources independently, containing multiple unknowns. We apply several constraints on the metric potentials as well as the newly added fluid source to solve these systems of equations. The impact of charge and the decoupling parameter σ is graphically analyzed on physical characteristics in the interior of a compact model 4U1820−30. We conclude that our first model is physically relevant for all parametric choices, however, the second solution becomes unstable only for σ=1.

Thermal stability and effects of thermal fluctuations on the static and spherically symmetric hairy black hole by gravitational decoupling

In this paper, we explore the thermodynamic aspects of the hairy black hole solution developed by gravitational decoupling in the spherical symmetry, considering its energy emission, Gibbs free energy, and thermal fluctuations. Our analysis involves the calculation of various quantities, including the Hawking temperature, geometric mass, and heat capacity to discuss the thermodynamic stability at local and global scales. To determine the temperature of the black hole, we utilize the first law of thermodynamics. Additionally, we evaluate the energy emission rate and establish its proportionality to the decoupling parameter α. By calculating the Gibbs free energy, we investigate the phase transition behavior through the swallowing tails of the hairy black holes. Furthermore, we derive the corrected entropy to examine the impact of thermal fluctuations on small and large black holes. We also calculated horizon radius r0, inner stable circular orbit rISCO , photon sphere radius rph, and shadows radius Rsh. Remarkably, the length scale parameters α (decoupling parameter) and β exhibit substantial influences on the thermodynamic properties of under consideration hairy black holes.

Implications of pressure anisotropy and complexity factor on the gravitational cracking phenomenon

In this study, we are investigating the stability of some stellar configurations evolving under anisotropic environment, in the background of gravitational cracking. The models we consider pertain to anisotropic versions of Durgapal–Fuloria model, which are established using the gravitational decoupling framework and present diverse scenarios involving complexity factor. Our analysis delves into the impact of anisotropy on the occurrence of cracking, as well as the influence of the complexity factor, which was introduced by Herrera (Phys Rev D 97:044010, 2018). We thoroughly examine how variations in the decoupling parameter and the compactness of the source contribute to the behavior of the radial force. It is found that more compact objects are more prone to gravitational cracking.

Accretion around a hairy black hole in the framework of gravitational decoupling theory

We investigate astrophysical accretion onto a static and spherically symmetric hairy black hole within the framework of gravitational decoupling. To achieve this goal, we examine the accretion procedure for several types of perfect fluids, including polytropic fluid and ultra-stiff, ultra-relativistic, radiation, and sub-relativistic isothermal fluids. Moreover, we determine the critical or sonic points for numerous fluid forms that are accreting onto the black hole by utilizing the Hamiltonian dynamical approach. Additionally, the closed form of the solutions are presented for a number of fluids, which are represented in phase diagram curves. We estimate the mass accretion rate of a static and spherically symmetric hairy black hole within the framework of gravitational decoupling. These findings are helpful in constraining the parameters of black holes while physical matter accretes onto the black holes.

Impact of charge on complexity analysis and isotropic decoupled solutions in gravity

In this paper, we formulate two exact charged solutions to the field equations by extending the domain of existing anisotropic models with the help of minimal gravitational decoupling in theory. For this, the anisotropic fluid distribution is considered as a seed source that is extended through the inclusion of a new gravitational source. The influence of the later matter configuration is controlled by the decoupling parameter. We formulate the field equations corresponding to the total matter source that are then decoupled into two distinct sets by implementing a transformation only on the radial metric coefficient. Both of these under-determined sets correspond to their parent sources. Some well-behaved forms of the metric potentials are taken into account to deal with the first set of equations. On the other hand, we solve the second set corresponding to an additional source by taking different constraints on the matter sector. We then consider the radius and mass of a compact star 4U 1820 − 30 to analyze the physical feasibility of the resulting solutions for a particular modified model. It is concluded that our resulting solutions show stable behavior for certain values of the decoupling parameter and charge.