Search

In this paper, we investigate the properties of a five-dimensional Ricci-flat black hole within the framework of the Space–Time–Matter theory. By employing the Klein–Gordon equation, we derive the wave function equations for both the mass dimensional coordinate and the radial dimensional coordinate. We present the analytical solutions for the wave function on the mass dimensional coordinate under two distinct scenarios. Remarkably, we observe the absence of quantum effects on the mass dimensional coordinate, which aligns with the absence of a barrier in the wave function equation. For the radial component, we employ the B-spline method to numerically solve its wave function. Our findings reveal the existence of Hawking radiation between the event horizon and the cosmological horizon, with the transmission and reflection probabilities being determined by the presence of a barrier. Furthermore, we discover a significantly higher probability of particle detection near the cosmological horizon, while the probability near the event horizon approaches zero. [ABSTRACT FROM AUTHOR]

The dark energy star is a hypothetical model proposed as an alternative to address problems related to the structure of black holes (BHs), such as the presence of singularities. While dark energy star models have been previously explored, their application to BHs remains unexplored. This paper aims to investigate the concept of dark energy stars and compare their properties to BHs. The primary objective is to explore the physical profiles of dark energy stars and evaluate their similarity to the physical properties of BHs described by the Schwarzschild solution. To achieve this, specific properties of the dark energy star models need to be satisfied in the context of BHs, and their physical profiles are studied. The metric function g r r proposed by M. R. Finch and J. E. F. Skea [Class. Quantum Grav. 6, 467 (1989)], as adopted by A. Banerjee, M. K. Jasim and A. Pradhan [Mod. Phys. Lett. A 35, 2050071 (2020), arXiv:1911.09546 [gr-qc]], is used and parametrized, making it close to BH spacetimes. The findings show that the model exhibits properties similar to BHs in terms of the stellar radius, compactness, surface redshift, and nature of gravity. Specifically, the dark energy star model behaves like BHs with a dark energy parameter ω = − 1 ∕ 3 , satisfying all energy conditions. However, it should be noted that the investigation is limited to static spherically symmetric cases and further studies are required to explore the model in rotating cases. Overall, this study sheds light on the potential of dark energy star models in explaining BH properties and presents promising avenues for further research in understanding the nature of BHs and dark energy. [ABSTRACT FROM AUTHOR]

In this paper, we study the Van der Waals black holes (the case b = 0) in the anti-de Sitter space under the effect of the linear extended uncertainty principle (EUP). The analysis was undertaken using deep learning by employing physics-informed neural networks in addition to the semi-classical approach, we have calculated the thermal quantities, including mass, volume, temperature, entropy, and Gibbs free energy. Additionally, we visually depict the effects of the EUP-term on the thermodynamic properties of the studied black holes. [ABSTRACT FROM AUTHOR]

For black holes with more than one horizon, the existence of a global temperature is not fully understood. This can affect the thermodynamics of these black holes to be unclear. In this paper, using the method of quantum tunneling, we find a global temperature for asymptotically AdS multi-horizon black holes appeared in three-dimensional quasitopological gravities given by T H = κ eff / 2 π , in which the effective surface gravity is related to the surface gravity of each horizon. We also find a global temperature for the asymptotically warped AdS3 black holes, having the same expression as the AdS multi-horizon black holes. In all of the cases the global temperature differs from the conventional Hawking temperature. [ABSTRACT FROM AUTHOR]

This paper investigates the static spherically symmetric vacuum solutions of Brans–Dicke Theory of Gravity. In this paper, we systematically derive the static spherically symmetric solutions by starting with the general static spherically symmetric anzats, discovering the nonzero Christoffel symbols, nonzero Ricci tensor components and the Ricci Scalar. These results allow us to rewrite the four Brans–Dicke gravitational field equations explicitly in terms of the metric components, the scalar field and its scalar potential. This paper systematically explains and shows how to modify these linear second-order ordinary differential equations in order to be able to find the solution of the scalar field, the metric components and the scalar potential analytically. We successfully find the most general solution of the static spherically symmetric vacuum solutions of Brans–Dicke gravity and the well-known Schwarzschild solution is recovered as the simplest solution. [ABSTRACT FROM AUTHOR]

In this paper, we provide a thermodynamical study of charged accelerating AdS black holes in the C -metric. In this connection, we first determine the mass of the given black hole and study their dependence on horizon radius and acceleration. Furthermore, following black hole mechanics, we also derive various quantities like Hawking temperature, entropy, pressure, volume, internal energy, Gibbs energy and Helmholtz energy. With the help of a graph, we study the effect of acceleration on these thermal quantities. Here, we observe that the impact of acceleration becomes more significant on the large horizons. To discuss stability and phase transition, we calculate specific heat. The graphical analysis suggests multiple phase transitions occur for the charged accelerating black hole in AdS spacetime. The system changes state at the critical point, where phase transition occurs. For the small black holes, the critical point at which the phase transition occurs is independent of the acceleration parameter. However, the critical horizon radius for large black holes depends on the acceleration parameter. For fast-accelerating black holes, a phase transition occurs at a small horizon radius to that of slowly accelerating black holes. [ABSTRACT FROM AUTHOR]

A microscopic derivation of the Bekenstein–Hawking entropy for the Schwarzschild black hole was presented earlier by using a nontrivial phase space. It was argued that the Schwarzschild black hole behaves like a 1 D quantum mechanical system. In this paper, we show that if we assume the phase space to obey the holographic principle and take the microscopic particles inside the quantum gravitational system to be ideal bosonic gas, we can derive the Bekenstein–Hawking entropy. The assumption of the phase space to follow the holographic principle such that the Schwarzschild black hole behaves as a 2 D system is very much in the spirit of our understanding of black holes than their behavior as a 1 D system. However, the argument suggests that the black hole be treated as a system with the equation of state P = ρ. [ABSTRACT FROM AUTHOR]

This paper examines the structure of a gravitational vacuum star (also known as gravastar) in the background of f (ℜ , 2) theory. This hypothetical object can be treated as a substitute of a black hole, with three regions: (i) the internal region, (ii) the intrinsic shell and (iii) the outer region. We examine these geometries using Finch–Skea metric for the radial metric component along with the particular f (ℜ , 2) model. We determine singularity-free solutions for both the inner as well as thin-shell domains. The smooth matching of the interior region with external Schwarzschild spacetime is obtained through Israel matching constraints. Finally, we study various characteristics of gravastar domains including the equation-of-state parameter, proper length, entropy, energy as well as surface redshift. It is found that the compact gravastar structure is a viable alternate to the black hole in the perspective of this gravity. [ABSTRACT FROM AUTHOR]

In this paper, we study the Dirac particle near the event horizon of the charged Bañados-Teitelboim-Zanelli (BTZ) black hole and Reissner–Nordström (R-N) black holes to obtain its energy spectrum for discussing the weak gravity conjecture (WGC). The corresponding energy has both real and imaginary parts. We encounter the quasi-normal mode. Because the considered black holes have mass M and charge Q , this property allows us to examine the WGC using the energy spectrum with specific conditions. We attempt to investigate the WGC for these black holes by utilizing the Dirac particle energy spectrum obtained near charged black holes. Also, we impose conditions on the energy spectrum of particles for which the WGC holds for charged black holes, i.e. Q ∕ M > 1. To approve the WGC near the event horizon of black holes, we determine that the Dirac particle has a specified charge viz q = − 1 2 ω and q = − 1 ln ( r + ℓ) for R-N and charged BTZ black holes, respectively. [ABSTRACT FROM AUTHOR]

Studies of accretion toward black holes are found in the literature where dark energy is chosen to act as the accreting agent. Studies of a dynamical system related to such a phase portrait are also available. In this paper, the central engine is opted to be embedded in a dark energy universe. Footprints of the dark energy equation of state are found in the black hole's metric chosen by us. Using the pseudo Newtonian method, the force complexity due to relativity is replaced with simplified terms. Dynamical system for a viscous accretion is constructed. Each point of this said system is a three-coordinated tuple presenting radial inward speed, sonic speed and specific angular momenta one after the other. A bent curve of center equilibrium is found. Two planes are seen which are, respectively, attractor and repeller. Every case is physically interpreted. For a viscous accretion onto a dark energy embedded black hole, it is followed that the center equilibrium points are forming a closed curve taking the origin on its own plane. Though the orbit of such a center equilibrium curve keeps only a part of it in the space of discussion. [ABSTRACT FROM AUTHOR]

In this paper, we discuss the tunneling of scalar particles near the event horizon of stationary and nonstationary Kerr–de Sitter black hole using Lorentz violation theory in curved space time. The modified form of Hamilton–Jacobi equation is derived from the Klein–Gordon equation by applying Lorentz violation theory. The Hawking temperatures derived from stationary and nonstationary Kerr–de Sitter black holes are modified due to Lorentz violation theory. It is noted that the change in Bekenstein–Hawking entropy and modified Hawking temperatures of stationary and nonstationary Kerr–de Sitter black hole not only depends on the black hole parameters but also on ether-like vectors u α . [ABSTRACT FROM AUTHOR]

In this paper, we discuss a mode sum regularization method for the self-force acting on a charged test particle moving around a Banados, Teitelboim and Zanelli (BTZ) black hole. First, we have calculated the self-force on each individual mode. Then we evaluated our result by summing up the contribution on each mode. We studied a general scheme for static black holes and then present the result for radial trajectories around (2 + 1) -dimensional charged BTZ black hole in Einstein–Gauss–Bonnet (EGB) gravity. We find that the parameter which is coupling (2 + 1) GR to Einstein–Gauss–Bonnet gravity has a significant impact on the self-force. [ABSTRACT FROM AUTHOR]

The inflationary 1-loop tensor power spectrum from a spectator scalar field with a sharp peak is calculated. Recent studies on primordial black holes suggest that the inflationary curvature perturbation may be huge on small scales. An enhanced curvature perturbation may arise from a drastic enhancement of spectator scalar field fluctuations. In this paper, using the in-in formalism, we calculate 1-loop quantum corrections to primordial gravitational waves by such a spectator field with a sharp peak in momentum space. We find scale-invariant loop corrections in this full quantum setup, in contrast to the sharply peaked corrections in the previously calculated scalar-induced tensor modes. Especially on super Hubble scales, the primordial gravitational waves are also amplified, which can be understood as a Bogoliubov transformation of the vacuum due to the enhanced scalar field. This mechanism allows us to probe the scalar field properties on extremely short-distance scales with the current and future cosmic microwave background and gravitational wave experiments, opening a novel window for inflationary cosmology. [ABSTRACT FROM AUTHOR]

In this paper, we present an analysis of the circular motion of test particles around a Schwarzschild-MOG black hole. Initially, our focus lies on studying the shadow cast by the spherically symmetric black hole within the framework of MOG gravity. Notably, we observe that the presence of MOG influences both the photon-sphere and the black hole's shadow, causing them to increase in size. Furthermore, our research reveals that the characteristic radii of massive particles in circular orbits around the Schwarzschild-MOG black hole, specifically the innermost stable circular orbits (ISCO) and marginally bound orbits, are greater than those observed in the Schwarzschild metric alone. Additionally, we examine the electromagnetic field structure when a black hole is subjected to an external uniform magnetic field. Our findings demonstrate that in the vicinity of the Schwarzschild-MOG black hole, the magnetic field exhibits non-uniform behavior, with field lines becoming more densely distributed. Lastly, we delve into the motion of charged particles around the Schwarzschild-MOG black hole in the presence of an external magnetic field. Our investigation highlights that the ISCO position for charged particles is consistently less than that for neutral particles, indicating a significant distinction between the two scenarios. [ABSTRACT FROM AUTHOR]

In this paper, we explore the black hole solutions with the rainbow deformed metric in the presence of the exponential form of the nonlinear electrodynamics with asymptotic Reissner–Nordström properties. We calculate the exact solution of metric function and explore the geometrical properties in the background of massive gravity. From the obtained solution, the existence of the singularity is confirmed in proper limits. Using the solutions, we also investigate the thermodynamic properties of the solutions by checking the validity of the first law of thermodynamics. Continuing the thermodynamic study, we investigate the conditions under which the system is thermally stable from the heat capacity and the Gibbs free energy. We also discuss the possible phase transition and the criticality of the system. It was found that the quantum gravitational effects of gravity's rainbow render the thermodynamic system stable in the vicinity of the singularity. Hence, we obtained a first-order phase transition which is interpreted as the large/small black hole phase transition. From the equation of state, it was found that after diverging at the singularity, the system evolves asymptotically into pressure-less dust as one moves away from the central singularity. We also calculated the quantum work using the change of the Helmholtz free energy. [ABSTRACT FROM AUTHOR]

This paper is devoted to studying the weak-field gravitational lensing properties of a 4D ESTGB black hole, which is surrounded by the plasma medium. The effects of the magnetic charges and the three plasma distribution models in the deflection of light around a 4D ESTGB black hole are investigated in detail. We find that the uniform plasma leads to a larger deflection of light rays in comparison with the singular isothermal sphere (SIS), the non-singular isothermal sphere (NSIS) models. Moreover, the deflection angle increases slightly as the absolute value of the magnetic charge decreases. Finally, we analyze the total magnification of image due to weak gravitational lensing around the black hole. The result shows that the presence of a uniform plasma medium remarkably enhances the total magnification whereas the non-uniform plasma reduces the total magnification. [ABSTRACT FROM AUTHOR]

It has been recently shown that the contribution between the horizons determines the Hawking temperature for a multi-horizon spacetime. In this paper, we apply the Hamiltonian–Jacobi method to compute the Hawking temperature for some multi-horizon spacetimes like Schwarzschild–de Sitter (SdS) spacetime, Reissner–Nordstrom–de Sitter (RNdS) spacetime and rotating BTZ (RBTZ) black hole spacetime and also arrive at the same conclusion. There are two contributions to the tunneling process of radiation. The combination of these two contributions gives the radiation with the Hawking temperature with an effective surface gravity. [ABSTRACT FROM AUTHOR]

In this paper, we have assumed that the thermodynamic pressure may be generated by the negative cosmological constant and the thermodynamic parameters of the n-dimensional asymptotically Anti-de Sitter (AdS)-Tangherlini black holes are identical with the polytropic gas and modified Chaplygin gas separately. The black hole mass, volume, entropy, and temperature have been written due to the assigned gases' thermodynamic system. We found the solutions of Einstein's field equations of n-dimensional black hole for polytropic gas and modified Chaplygin gas. The null energy condition, weak energy condition, strong energy condition, and dominant energy condition have been examined for the fluid sources in n-dimensional black hole system due to both the gases. We found that the four energy conditions completely depend on the model parameters and the dimensions of the spacetime. We have studied the heat engine phenomena for both the black holes and analyzed the work done with the efficiencies due to the Carnot and other cycles. [ABSTRACT FROM AUTHOR]

This paper focuses on the issues of motion of various kinds of charged, magnetized, and neutral test particles in the vicinity of static and spherically symmetric electrically charged black holes in the Einstein-Æther gravitational theory. Our purpose here is to analyze the effects of the free parameters occurring in the Einstein-Æther theory for particle motion in curved spacetime. Specifically, we have studied the stability of circular and radially varying orbits of different kinds of particles by varying the free parameters c 1 3 and c 1 4 , and also varying the particle's specific energy, specific angular momentum, and electric charge of the black hole. As a special case, we investigate the charged particle motion around the black holes with a uniform magnetic field by checking the characteristics of the particle's innermost stable circular orbit. Finally, we propose few values of the parameters c 1 3 and c 1 4 which mimic the behavior of spin of a Kerr black hole to model an astrophysical black hole. [ABSTRACT FROM AUTHOR]

In this paper we consider a BTZ black hole with minimum length which has been introduced through the probability density of the ground state of the hydrogen atom. We analyzed the effect of the minimum length by calculating the thermodynamic quantities such as temperature and entropy and verified the stability of the black hole by computing the specific heat capacity. [ABSTRACT FROM AUTHOR]

In this paper, we analyze the tidal effects of anti-de Sitter charged black holes. The tidal force components are obtained by Riemann tensor on tetrad basis and geodesic deviation equation. The radial components of tidal force have the same changes outside the horizon if the charge mass ratio is closer to each other, unlike in Reissner–Nordström BHs. The angular tidal forces increase infinitely with increase of charge and Λ. We derive the geodesic deviation equation on a neutral body for anti-de Sitter torus like charged black hole. We find the radial and angular tidal forces on the neutral body. Furthermore, we express the graphical behavior of radial and angular components for the most suitable initial conditions. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the innermost stable circular orbit (ISCO) of spinning particles around a rotating black hole surrounded by the perfect fluid dark matter (PFDM). The motion of spinning particles is derived by Mathisson–Papapetrou–Dixon equation and the ISCO parameters are obtained by the radial effective potential. The effect of PFDM density parameter on the motion of spinning particles is analyzed. The results show that the effect of PFDM is nonlinear, and the radius of ISCO varies nonmonotonically with PFDM density parameter. [ABSTRACT FROM AUTHOR]

In this paper, we have studied the reconstruction formalism of the Dirac–Born–Infeld (DBI)-essence scalar field model in the background of non-metric gravity or f (Q) gravity which is controlled by the deformation or non-metricity scale Q. The deformation is caused by the fifth dimension of wrapped compact spaces in brane cosmology. The fifth dimension of that wrapped space is controlled by the D-Brane tension T (ϕ). Hence, we have reconstructed the formalism of DBI scalar field energy densities and pressures using the coupling of deformation geometry and brane scalar fields, i.e. f (Q) and DBI-Scalar fields. The accretion of dark energy onto black holes and wormholes and its critical analysis had been studied with this reconstructed model. The validity of energy conditions has been studied. We have assumed four types of singularity resolutions of the scale factor to investigate the nature of the black hole and wormhole masses due to accretion. Graphically, the physical quantities like mass, kinetic and potential energies have been analyzed for DBI-essence model in the background of f (Q) gravity. [ABSTRACT FROM AUTHOR]

In this paper, we take the view that the area of a black hole's event horizon is quantized, A = l P 2 (4 ln 2) N , and the associated degrees of freedom are finite in number and of fermionic nature. We then investigate general aspects of the entropy, S BH , our main focus being black hole self-similarity. We first find a two-to-one map between the black hole's configurations and the ordered partitions of the integer N. Hence, we construct from there a composition law between the subparts making the whole configuration space. This gives meaning to black hole self-similarity, entirely within a single description, as a phenomenon stemming from the well-known self-similarity of the ordered partitions of N. Finally, we compare the above to the well-known results on the subleading (quantum) corrections, which necessarily require different (quantum) statistical weights for the various configurations. [ABSTRACT FROM AUTHOR]

In this paper, we adapted the Appleby–Battye–Starobinsky model of F (R) gravity towards describing double cosmological inflation and formation of primordial black holes with masses up to 1 0 1 9  g in the single-field model. We found that it is possible to get an enhancement of the power spectrum of scalar curvature perturbations to the level beyond the Hawking (black hole evaporation) limit of 1 0 1 5  g, so that the primordial black holes resulting from gravitational collapse of those large primordial perturbations can survive in the present universe and form part of cold dark matter. Our results agree with the current measurements of cosmic microwave background radiation within 3 σ but require fine-tuning of the parameters. [ABSTRACT FROM AUTHOR]

This paper is devoted to studying the structure of gravitationally vacuum condensate stars under the influence of matter and geometry coupled gravity. This alternative to black hole comprises three domains, i.e. interior, exterior and thin-shell. We investigate such regions by considering particular equations of state for a specific model of energy–momentum squared gravity. The nonsingular solutions of field equations are obtained to describe the interior region of gravastar and the Schwarzschild spacetime represents the exterior region. The junction conditions are used to match interior and exterior domains while Lanczos equations provide the surface density and pressure at thin-shell. We investigate various attributes of gravastar such as the equation of state parameter, entropy, proper length as well as energy. The physical features of a gravitationally vacuum star indicate a linear relationship with the thickness of the shell and provide a viable structure similar to general relativity. [ABSTRACT FROM AUTHOR]

It is found difficult to construct a complete general relativistic theory for an accretion disc around a relativistic compact star. There exists a trend to reproduce the effects of general relativistic attraction by using a pseudo-Newtonian approach. One such pseudo-Newtonian force for a spinning black hole sitting in quintessence background is constructed in this paper. Comparison with general relativity at different parametric values is picturised thoroughly. Next, an accretion model using this newly constructed pseudo-Newtonian force is built. The radial inward speed gradient is found to be expressed as a ratio of two functions. It can be realized easily that among these two functions, the denominator might vanish for a particular value of radial speed in the interval zero to speed of light. To make the flow physical, the numerator should vanish at the same radial distance. This will ultimately generate two speed profiles starting from the particular radial distance. This is the cause of generation for accretion and wind branches. It has been followed that the disc is truncated at a finite distance due to the fact that the specific angular momentum becomes larger than the Keplerian angular momentum beyond that. Effects of the spin of the central gravitating object are followed along with the intense effect of the quintessence parameters concerned. Accretion and wind density profiles are also studied to find the density variations near the central engine. Ratio of shear viscosity to entropy density is analyzed in the presence of quintessence for viscous accretion flows. [ABSTRACT FROM AUTHOR]

In this paper, the affiliations of Bobur Turimov should be reordered as follows:Bobur TurimovNew Uzbekistan University, Mustaqillik Avenue 54, Tashkent 100007, UzbekistanCentral Asian University, Milliy Bog St. 264, Tashkent 111221, UzbekistanUlugh Beg Astronomical Institute, Astronomy St. 33, Tashkent 100052, UzbekistanReported by Author; Author; Author [Extracted from the article]

This paper studies the influence of charge on a compact stellar structure also regarded as vacuum condensate star in the background of f (ℜ , 2) 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. [ABSTRACT FROM AUTHOR]

In this paper, we explore the geodesics motion of neutral test particles and the process of energy extraction from a regular rotating Hayward black hole (BH). We analyze the effect of spin as well as deviation parameter g , on ergoregion, event horizon and static limit of the said BH. By making use of geodesic equations on the equatorial plane, we determine the innermost stable circular and photon orbits. Moreover, we investigate the effective potentials and effective force to have information on motion and the stability of circular orbits. On studying the negative energy states, we figure out the energy limits of Penrose mechanism. Using Penrose mechanism, we found expression for the efficiency of energy extraction and observed that both spin and deviation parameters contribute to the efficiency of energy extraction. Finally, the obtained results are compared with that acquired from Kerr and braneworld Kerr BHs. [ABSTRACT FROM AUTHOR]

In this paper, the Joule–Thomson expansion of Born–Infeld AdS black holes in the consistent Aoki–Gorji–Mukohyama theory of 4D Einstein–Gauss–Bonnet gravity is studied in the extended phase space. We further analyze the effect of parameters α and β on the inversion curves and plot the inversion and isenthalpic curves in the T – P plane, which can determine the cooling–heating regions. [ABSTRACT FROM AUTHOR]

In this paper, we study the quasinormal modes for scalar, electromagnetic, and gravitational axial perturbations in the Hayward regular black hole surrounded by quintessence (HBH- ω q ). Using the third-order WKB approximation, we can determine the dependence of the quasinormal modes on the parameters of the regular black hole and the parameters on the test fields. We also determine the greybody factor, giving transmission and reflection coefficients of the scattered wave through the effective potentials in the WKB approximation using numerical analysis. [ABSTRACT FROM AUTHOR]

In this paper, we explore thermodynamics, thermal stability, effects of logarithmic corrections on thermodynamic quantities and phase transitions of spherically symmetric regular black hole with the de Sitter core. We first calculate the expressions for Hawking temperature as well as heat capacity and investigate its thermal stability. We also discuss the effects of logarithmic corrections on thermodynamical quantities such as pressure, Gibbs–Helmholtz free energy, internal energy and enthalpy of the system. Finally, we analyze the behavior of Hawking temperature as well as specific heat capacity of the regular black hole versus entropy for different values of the de Sitter parameter (b). It is found that Hawking temperature changes its phase from positive to negative and heat capacity changes its phase from negative to positive for large values of b. [ABSTRACT FROM AUTHOR]

We are engaged in studying thermodynamics of black holes from quantum mechanical perspective and already have published a series of papers. We first showed, based on certain assumptions for quantum mechanical nature of black holes, that they can be thought to be immersed in a thermal bath, i.e. rest of the universe. Of course, this consideration is required to study the thermodynamics of the black holes. We were able to find out the conditions of thermal stability for a black hole with arbitrary number of hairs in arbitrary dimensional spacetime. They came in form of a series of inequalities, connecting second-order derivatives of black hole mass with respect to its area and all the hairs. We then introduced the concept of "Quasi stability", based on partial fulfillment of stability criteria, for thermally decaying black holes. We had also calculated the fluctuations for different hairs of a stable black hole. In this paper, we extend this calculation for charged rotating quasi-stable black holes. These fluctuations are interestingly found to be similar to that of stable black holes in certain aspects. [ABSTRACT FROM AUTHOR]

In this paper, we searched two new exact solutions of Einstein's field equations for modeling of compact cold stars using embedded class one spacetime continuum. We find out the expressions for pressure, density, anisotropy, redshift, metric potentials and other physical variables in terms of algebraic and trigonometric expressions and observe that all variables show well-behaved trends inside the compact stellar configurations. The causality condition is well maintained by our stellar models, i.e. the radial velocity and transverse velocity are less than l. The stability of our models is assessed via different stability criteria. The Buchdahl condition holds good for our solution. Herrera's cracking method is applied to check the stability of stellar models. We generate anisotropic compact star models, whose masses and radii are in close agreement with the observed values for compact stars 4U 1538-52, LMCX-4, PSRJ1614-2230. A comparative analysis of the proposed models is carried out based on two different solutions reported in the paper. The appropriate graphical analysis is provided to authenticate the viability of the models. [ABSTRACT FROM AUTHOR]

There is a special interest to understand the dynamical properties of the accretion disk created around the newly formed black hole due to the supermassive black hole binaries which merge inside the gaseous disk. The newly formed black hole would have a kick velocity up to thousands of km/s that drives a perturbation on a newly accreted torus around the black hole. Some of the observed supermassive black holes at the center of the Active Galactic Nucleus (AGN) move with a certain velocity relative to its broader accretion disk. In this paper, the effects of the kicked black holes onto the infinitesimally thin accreted torus are studied by using the general relativistic hydrodynamical code, focusing on changing the dynamics of the accretion disk during the accretion disk–black hole interaction. We have found that the non-axisymmetric global mode m = 1 inhomogeneity, which causes a spiral-wave-structure, is excited on the torus due to kicked black hole. The higher the perturbation velocity produced by the kicked black hole, the longer the time the torus takes to reach the saturation point. The created spiral density waves which rapidly evolve into the spiral shocks are also observed from the numerical simulations. The spiral shock is responsible for accreting matter toward the black hole. First, the spiral-wave-structure is developed and the accretion through the spiral arms is stopped around the black hole. At the later time of simulation, the formed spiral shocks partly cause the angular momentum loss across the torus. [ABSTRACT FROM AUTHOR]

In this paper, we have used the reconstructed Dirac–Born–Infeld (DBI)-essence dark energy density to modify the mass accretions of black holes and wormholes. In general, the black hole mass accretion does not depend on the metric or local Einstein geometry. That is why we have used a generalized mechanism by reconstructing the DBI-essence dark energy reconstruction with f (R) gravity. We have used some particular forms of the scale factor to analyze the accretion phenomena. We have shown the effect of cosmic evolution in the proper time variation of black hole mass accretion. Finally, we have studied the validity of energy conditions and analyzed the Type I–IV singularities for our reconstructed model. [ABSTRACT FROM AUTHOR]

Recently great interest has been devoted toward a better understanding of a possible deep relation between large size structures we observe today in the universe and the quantum fluctuations at Planck time. Within such a context this paper provides us with a procedure for how to obtain a faithful description of the Bohr energy levels for hydrogen like atoms, starting from a generalization of a quantum relation for primordial black holes' masses at Planck time. The key role of quantum mechanics in such a description is emphasized and the classical correspondence taking us from Newton's law for interacting masses to Coulomb's law for interacting charges evidenced. [ABSTRACT FROM AUTHOR]

Direct detection of gravitational waves from several compact binary coalescences has ushered in a new era of astronomy. It has opened up the possibility of detecting ultralight bosons, predicted by extensions of the Standard Model, from their gravitational signatures. This is of particular interest as some of these hypothetical particles could be components of dark matter that are expected to interact very weakly with Standard Model particles, if at all, but they would gravitate as usual. Ultralight bosons can trigger superradiant instabilities of rotating black holes and form bosonic clouds that would emit gravitational waves. In this paper, we present an overview of such instabilities as gravitational wave sources and assess the ability of current and future detectors to shed light on potential dark matter candidates. [ABSTRACT FROM AUTHOR]

In this paper, by using a recently found black hole solution in the framework of the Poincaré gauge theory of gravity, we study gravitational lensing for a system where the lens is a static spherically symmetric black hole. By analyzing the equations of motion for light rays in a spacetime with torsion, we derive the deflection angle as the light emitted from a source pass through near the black hole and numerically solve the resulting integral. We also study the effects of torsion on the position of images. The results show that the presence of torsion slightly alters both the deflection angle and position of images in this setup. [ABSTRACT FROM AUTHOR]

In this paper, we consider a static black hole in f (R) gravity. We recapitulate the expression for corrected thermodynamic entropy of this black hole due to small fluctuations around equilibrium. Also, we study the geometrothermodynamics (GTD) of this black hole and investigate the adaptability of the curvature scalar of geothermodynamic methods with phase transition points of this black hole. Moreover, we study the effect of correction parameter on thermodynamic behavior of this black hole. We observe that the singular point of the curvature scalar of Ruppeiner metric coincides completely with zero point of the heat capacity and the deviation occurs with increasing correction parameter. [ABSTRACT FROM AUTHOR]

In this paper, a brief analysis of repeated and overlapped gamma-ray bursts, fast radio bursts and gravitational waves is done. These signals may not be emitted by isolated cataclysmic events and we suggest interpreting some of them within the impenetrable black hole model, as the radiation reflected and amplified by the black hole horizons. [ABSTRACT FROM AUTHOR]

Various proposals for gravitational entropy densities have been constructed from the Weyl tensor. In almost all cases, though, these studies have been restricted to general relativity, and little has been done in modified theories of gravity. However, in this paper, we investigate the simplest proposal for an entropy density constructed from the Weyl tensor in five-dimensional Gauss–Bonnet gravity and find that it fails to reproduce the expected entropy of a black hole. [ABSTRACT FROM AUTHOR]

As an intriguing topological defect, global monopole's influence on behaviors of black holes has always been anticipated but still remains obscure. Analyzing the thermodynamics of charged Anti-de Sitter (AdS) black hole incorporating a global monopole manifests that the black hole undergoes a Van der Waals-like first-order phase transition near the critical point. This paper concentrates on further investigating the transition, aiming at clarifying how the global monopole affects the criticality and microstructure of the charged AdS black holes. As a highlight, this research is implemented by employing new state parameters other than (T, P, V) description and contributes to deeper understanding the rich critical phenomena and phase structure of black holes. [ABSTRACT FROM AUTHOR]

In this paper, we discuss remnants of the Bardeen regular black hole motivated by using the concept of thermal fluctuations. First, we derive the equilibrium values of various thermodynamic quantities like entropy, Hawking temperature, pressure, internal energy, Helmholtz free energy and Gibbs free energy in the non-extended phase space. We then discuss geometrothermodynamics (GTD) of Bardeen black hole to study its stability. Next, we estimate the size of black hole remnant in terms of some known parameters of the black hole solution. Motivated by the fact that estimation of size, characteristics and stability of remnants of black holes could further increase our understanding of binary collisions, information loss paradox and dark energy, the black hole remnant, which gives an idea about stable mass left over after evaporation of black hole, is seen to owe its presence due to thermal fluctuations. We see that the thermal fluctuations bring an overall increase in entropy curve. However, in presence of thermal fluctuations, a positive kink, which signifies a maximum increase in the value of entropy, occurs at a certain value of horizon, which is exactly equal to the remnant radius. We observe that the thermal fluctuations, which are characteristics of quantum gravity, lead to stable values of thermodynamic quantities near the remnant radius. In presence of thermal fluctuations, we then derive various corrected thermodynamic potentials and also discuss the validity of first law of black hole thermodynamics for Bardeen black hole. [ABSTRACT FROM AUTHOR]

In this paper, we consider three-dimensional massive gravity's rainbow and obtain black hole solutions in three different cases of Born–Infeld, logarithmic, and exponential theories of nonlinear electrodynamics. We discuss the horizon structure and geometrical properties. Then, we study thermodynamics of these models by considering the first-order quantum correction effects, which appear as a logarithmic term in the black hole entropy. We discuss such effects on the black hole stability and phase transitions. We find that due to the quantum corrections, the second-order phase transition happens in Born–Infeld and logarithmic models. We obtain the modified first law of black hole thermodynamics in the presence of logarithmic corrections. [ABSTRACT FROM AUTHOR]

This paper explores the influence of special type of higher order generalized uncertainty principle on the thermodynamics of five-dimensional black hole in Einstein–Gauss–Bonnet gravity coupled to nonlinear electrodynamics. We examine the corrected thermodynamical properties of the black hole with some interesting limiting cases k → 0 and α → 0 and compared our results with usual thermodynamical relations. We observe that the influence of GUP correction stabilizes the BH and BH solution remains physical throughout the region of horizon radius. In this framework, we also uncover the relationship of shadow radius and quasinormal modes of the mentioned black hole. We conclude that shadow radius of our considered black hole is a perfect circle and it decreases with increasing values of charge and Gauss–Bonnet parameter. We also verify the inverse relation between the quasinormal modes frequencies and shadow radius, i.e. quasinormal modes should increase with increasing values of Gauss–Bonnet parameter and electric charge. [ABSTRACT FROM AUTHOR]

In this paper, we derived an exact solution of the spherically symmetric Hayward black hole surrounded by perfect fluid dark matter (PFDM). By applying the Newman–Janis algorithm, we generalized it to the corresponding rotating black hole. Then, we studied the shadows of rotating Hayward black hole in PFDM. The apparent shape of the shadow depends upon the black hole spin a , the magnetic charge Q and the PFDM intensity parameter k (k < 0). The shadow is a perfect circle in the non-rotating case (a = 0) and a deformed one in the rotating case (a ≠ 0). For a fixed value of a , the size of the shadow increases with the increasing | k | , but decreases with the increasing Q. We further investigated the black hole emission rate. We found that the emission rate decreases with the increasing | k | (or Q) and the peak of the emission shifts to lower frequency. Finally, we discussed the observational prospects corresponding to the supermassive black hole Sgr A ∗ at the center of the Milky Way. [ABSTRACT FROM AUTHOR]

In this paper, we attempt to further study the heat engine efficiency for the regular black hole (BH) with an anti-de Sitter (AdS) background where the working material is the Hayward-AdS (HAdS) BH. In the extended phase space, we investigate the heat engine efficiency of the HAdS BH by defining the cosmological constant as the thermodynamic pressure P and deriving the mechanical work from the PdV terms. Then, we obtain the relation between the efficiency and the entropy/pressure and plot these function figures. Meanwhile, we compare the relation between the HAdS BH with that of the Bardeen-AdS (BAdS) BH, where it is found that the efficiency of the HAdS BH increases with increase in the magnetic charge q in contrast to that of the BAdS BH decrease with increase in the magnetic charge q. We found that the HAdS BH is more efficient than the BAdS BH, and guess that it is related to the BH structure. [ABSTRACT FROM AUTHOR]

The study of thermodynamics in the view of the Hamiltonian approach is the newest tool to analyze the thermodynamic properties of the black holes (BHs). In this paper, we investigate the thermodynamics of d-dimensional (d > 3) asymptotically Anti-de Sitter (AdS) BHs. A thermodynamic representation based on symplectic geometry is introduced in this paper. We extend the thermodynamics of d-dimensional charged AdS BHs in the views of a Hamiltonian approach. Firstly, we study the thermodynamics in reduced phase space and correlate with the Schwarzschild solution. Then we enhance it in the extended phase space. In an extended phase space, the thermodynamic equations of state are stated as constraints. We apply the canonical transformation to analyze the thermodynamics of the said type of BHs. We plot P - v diagrams for different dimensions d taking the temperatures T < T c , T = T c and T > T c and analyze the natures of the graphs and the dependences on d. In these diagrams, we point out the regions of coexistence. We also examine the phase transition by applying "Maxwell's equal area law" of the said BHs. Here, we find the regions of coexistence of two phases which are also depicted graphically. Finally, we derive the "Clapeyron equation" and investigate the latent heat of isothermal phase transition. [ABSTRACT FROM AUTHOR]