Class Of Black Hole Solutions Research Articles

Black holes in multimetric gravity

We construct a wide class of black hole solutions to the general theory of ghost-free multimetric gravity in arbitrary spacetime dimension, extending and generalizing the known results in four-dimensional dRGT massive gravity and bigravity. The solutions are split into three generic classes based on whether the metrics can be simultaneously diagonalized—one of which does not exist in dRGT massive gravity nor bigravity, and is only possible when one has more than two interacting metric fields. We also linearize the general multimetric theory to determine the dynamics of the massive spin-2 modes, including examples where this can be done analytically, and use the linear theory to discuss the stability of the four-dimensional multi-Schwarzschild and multi-Kerr solutions. We explain how the instabilities that plague these solutions in dRGT massive gravity and bigravity carry across to the general multimetric theory, touching upon ideas of dimensional deconstruction to make sense of the results. Published by the American Physical Society 2024

A Bare and Gravitationally Dressed Electron Formed from Kerr–Newman Black Hole

The Kerr–Newman (KN) electron model, based on the classical KN black hole solution, is modified by adding a “mirror” sheet of KN metric corresponding to a positron, that creates a heavy electron-positron vacuum core dressed by gravity, and allows us to consider the bare and dressed electron separately. The bare electron is formed as a massless relativistic ring string and is responsible for the wave properties of the electron, while the heavy supersymmetric vacuum core receives the additional mass-energy from two Wilson loops dragged by the KN gravitational field, thus creating a magnetically coupled monopole-antimonopole pair. As a result, the KN electron becomes consistent with wave nature of quantum electron and its gravitational interaction increases dramatically from Planck to Compton scale.

Computational analysis of thin-shell with scalar field for class of new black hole solutions in metric-affine gravity

The aim of this study is to investigate the geometric structure of a thin-shell within the context of metric-affine gravity. To accomplish this, we employ a cut and paste approach to match the inner Minkowski spacetime and an outer newly calculated class of black hole solutions in metric-affine gravity. These solutions are Reissner–Nordström-like black holes with shear, spin, dilation, electric, magnetic charges, and a cosmological constant. Using the Klein–Gordon equation of motion, we analyze the dynamics of the thin-shell configuration under both massive and massless scalar fields. We find that the scalar field affects thin-shell dynamics and can lead to interesting effects such as dynamics and stability configurations. We demonstrate that the linearized radial perturbation approach employing a phantom-like equation of state, such as quintessence, dark energy, and phantom energy, reveal stable configurations of the thin-shell located beyond the expected position of the event horizon of the exterior manifold. We also find that the stability of the thin-shell depends strongly on the parameters of the black hole solutions. Our results shed light on the dynamics of thin-shells in the context of metric affine gravity with scalar fields and provide new insights into the behavior of black hole solutions in this theory. It is concluded that the thin-shell composed of quintessence and dark energy shows the more stable configuration for the choice of Reissner-Nordström-like black holes with shear, spin, and dilation charges.

Thermodynamics of dilaton black holes charged with a higher-dimensional Coulomb-like field

AbstractThe field equations are written explicitly in the framework of higher-dimensional Einstein-dilaton gravity theory, which is coupled to non-linear electrodynamics. It is proved that this theory is confronted with the problem of indeterminacy. By this we mean that the number of unknowns is one more than the unique differential equations. Analytical solutions are obtained by the use of power-law and exponential ansatz functions, separately. It is found that this theory in the presence of a Coulomb-like electric field, inspired by non-linear electrodynamics, admits two novel classes of black hole solutions for each of the ansatz functions. Under the influence of the dilaton field, the asymptotic behavior of the solutions is neither flat nor anti-de Sitter. Through comparison of the results it is shown that, under some simple conditions, both of the ansatz functions lead to the same results. It is illustrated that our exact solutions can produce two-horizon, one-horizon, and horizonless black holes. The validity of the first law of black hole thermodynamics is investigated by use of a Smarr-type mass formula. The thermal stability of the black holes is analyzed by making use of the canonical ensemble and geometrical methods, separately. The results of these two alternative approaches are compared by the use of plots.

Regular solutions for black strings and torus-like black holes

In this letter, we extend the recent black hole solution with spherical symmetry [Phys. Lett. B \textbf{835} (2022), 137546], to a new class of black hole solutions with different topology, namely, a torus-like black hole and a black string in the presence of the cosmological constant. We have used the regularized expressions for the gravitational and the electromagnetic potentials, then we derived the corrections to the energy density and, finally, the black hole solutions are obtained which are regular in the limit $r \to 0$. Interestingly, it is found that the total mass of the black hole is corrected due to the regularized self-energy of the electrostatic field. In the special limit, we recover the well-known solutions in the literature.

The effects of running gravitational coupling on three dimensional black holes

In the present work, we investigate the consequences of running gravitational coupling on the properties of the three-dimensional BTZ black hole. We take as starting point the functional form of gravitational coupling obtained in the context of asymptotic safe gravity theory. By using the standard scale setting relation where ksim xi /r^n, we compute the solution of the Einstein field equations. We get and analyze the horizon and the thermodynamic properties of this new class of black hole solutions. The impact of the scale-dependent parameter xi on the cosmological “constant” and metric functions are briefly discussed. We find that the null energy condition is also violated in this setup when scale-dependent gravity and Newton’s coupling (coming from the asymptotic safety scenario of gravity) are simultaneously taken into account.

Gravitational lensing and shadow of charged black holes in the low-energy limit of string theory

In this work, we investigate the shadow cast and strong field gravitational lensing of a new class of black hole solutions in dilaton gravity where dilaton field is coupled with nonlinear Maxwell invariant [Younesizadeh et al. in Int J Mod Phys A 34(35):1950239]. The space-time is a stationary axisymmetric geometry. The key part in our investigations is finding the effect of dilaton parameter N on the size of shadows and the energy emission rate. As the N parameter increases, the size of black hole shadow increases. Also, the energy emission rate increases with increase in the dilaton parameter N. By supposing the gravitational field of the supermassive object at the heart of Milky Way galaxy described by this metric, we estimated the numerical values of the observables for gravitational lensing in the strong field limit.

Scalar and Dirac quasinormal modes of scalar-tensor-Gauss-Bonnet black holes * *Supported by the National Natural Science Foundation of China (NNSFC) (11805166), Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP), Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro (FAPERJ), Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

This study explores the scalar and Dirac quasinormal modes pertaining to a class of black hole solutions in the scalar-tensor-Gauss-Bonnet theory. The black hole metrics in question are novel analytic solutions recently derived in the extended version of the theory, which effectively follows at the level of the action of string theory. Owing to the existence of a nonlinear electromagnetic field, the black hole solution possesses a nonvanishing magnetic charge. In particular, the metric is capable of describing black holes with distinct characteristics by assuming different values of the ADM mass and the magnetic charge. This study investigates the scalar and Dirac perturbations in these black hole spacetimes; in particular, we focus on two different types of solutions, based on distinct horizon structures. The properties of the complex frequencies of the obtained dissipative oscillations are investigated, and the stability of the metric is subsequently addressed. We also elaborate on the possible implications of this study.

Quasinormal modes for non-minimally coupled scalar fields in regular black hole spacetimes: Grey-body factors, area spectrum and shadow radius

Black hole perturbation theory is a useful approach to study interactions between black holes and fundamental fields. A particular class of black hole solutions arising out of modification of Einstein’s general theory of relativity are regular black holes (RBHs) which can be constructed using a nonlinear electrodynamic Lagrangian. Because of their importance, we are interested in studying the behavior of three kinds of such RBHs under perturbations generated by an external field. Indeed, we investigate the quasinormal modes (QNMs) of a massive scalar field propagating near the RBHs which is non-minimally coupled to the Ricci scalar-tensor of background geometry. We will attempt to find the low-lying quasinormal frequencies of the perturbations by using WKB approximation. We shall also study the relationship between the QNMs and some characteristic properties of black holes such as grey-body factors, area quantization, and shadow radius.

Poynting vector, super-Poynting vector, and principal observers in electromagnetism and general relativity

In electromagnetism, the concept of Poynting vector as measured by an observer is well known. A mathematical analogue in general relativity is the super-Poynting vector of the Weyl tensor. Observers for which the (super-)Poynting vector vanishes are called principal. When, at a given point, the electromagnetic field is non-null, or the gravitational field is of Weyl–Petrov type I or D, principal observers instantaneously passing through that point always exist. We survey characterizations of such observers and study their relation to arbitrary observers. In the non-null electromagnetic case it is known that, given any observer, there is a principal observer which moves relative to the first in the direction of his Poynting vector. Replacing Poynting by super-Poynting yields a possible gravitational analogue; we show that this analogy indeed holds for any observer when the Petrov type is D, but only for a one-dimensional variety of observers when the Petrov type is I. We provide algorithms to obtain the principal observers directly from the electric and magnetic fields (in the electromagnetic case) or electric and magnetic parts of the Weyl tensor (in the gravitational case) relative to an arbitrary observer. It is found that in Petrov type D doubly aligned non-null Einstein–Maxwell fields (which include all classical charged black hole solutions) the Poynting and super-Poynting vectors are aligned, at each point and for each observer, and the principal observers coincide. Our results are illustrated in simple examples.

Yang\u2013Mills black holes in quasitopological gravity

In this paper, we formulate two new classes of black hole solutions in higher curvature quartic quasitopological gravity with nonabelian Yang–Mills theory. At first step, we consider the SO(n) and SO(n-1,1) semisimple gauge groups. We obtain the analytic quartic quasitopological Yang–Mills black hole solutions. Real solutions are only accessible for the positive value of the redefined quartic quasitopological gravity coefficient, mu _{4}. These solutions have a finite value and an essential singularity at the origin, r=0 for space dimension higher than 8. We also probe the thermodynamic and critical behavior of the quasitopological Yang–Mills black hole. The obtained solutions may be thermally stable only in the canonical ensemble. They may also show a first order phase transition from a small to a large black hole. In the second step, we obtain the pure quasitopological Yang–Mills black hole solutions. For the positive cosmological constant and the space dimensions greater than eight, the pure quasitopological Yang–Mills solutions have the ability to produce both the asymptotically AdS and dS black holes for respectively the negative and positive constant curvatures, k=-1 and k=+1. This is unlike the quasitopological Yang–Mills theory which can lead to just the asymptotically dS solutions for Lambda >0. The pure quasitopological Yang–Mills black hole is not thermally stable.

The Quantum Regularization of Singular Black-Hole Solutions in Covariant Quantum Gravity.

An excruciating issue that arises in mathematical, theoretical and astro-physics concerns the possibility of regularizing classical singular black hole solutions of general relativity by means of quantum theory. The problem is posed here in the context of a manifestly covariant approach to quantum gravity. Provided a non-vanishing quantum cosmological constant is present, here it is proved how a regular background space-time metric tensor can be obtained starting from a singular one. This is obtained by constructing suitable scale-transformed and conformal solutions for the metric tensor in which the conformal scale form factor is determined uniquely by the quantum Hamilton equations underlying the quantum gravitational field dynamics.

Quasinormal modes of hot, cold and bald Einstein\u2013Maxwell-scalar black holes

Einstein–Maxwell-scalar models allow for different classes of black hole solutions, depending on the non-minimal coupling function f(phi ) employed, between the scalar field and the Maxwell invariant. Here, we address the linear mode stability of the black hole solutions obtained recently for a quartic coupling function, f(phi )=1+alpha phi ^4 (Blázquez-Salcedo et al. in Phys. Lett. B 806:135493, 2020). Besides the bald Reissner–Nordström solutions, this coupling allows for two branches of scalarized black holes, termed cold and hot, respectively. For these three branches of black holes we calculate the spectrum of quasinormal modes. It consists of polar scalar-led modes, polar and axial electromagnetic-led modes, and polar and axial gravitational-led modes. We demonstrate that the only unstable mode present is the radial scalar-led mode of the cold branch. Consequently, the bald Reissner–Nordström branch and the hot scalarized branch are both mode-stable. The non-trivial scalar field in the scalarized background solutions leads to the breaking of the degeneracy between axial and polar modes present for Reissner–Nordström solutions. This isospectrality is only slightly broken on the cold branch, but it is strongly broken on the hot branch.

Hawking evaporation of black holes in massive gravity

We study the Hawking evaporation of a class of black hole solutions in dRGT massive gravity, in which the graviton mass gives rise to an effective negative cosmological constant. We found that the effective emission surface can be either proportional to the square of the effective AdS length scale, or corresponds to the square of the impact parameter of the null geodesic that falls onto the photon orbit of the black hole. Furthermore, depending on the black hole parameters, the emission surface could switch from one to another as the black hole loses mass during the evaporation process. Furthermore, the black holes can either evaporate completely or become a remnant at late time. Our result is more generally applicable to any asymptotically anti-de Sitter-like black hole solution in any theory whose metric function has a term linear in the coordinate radius, with massive gravity being only a concrete example.

BH solutions with toroidal horizon in dilaton gravity inspired by power-law electrodynamics: PV criticality and quasinormal modes

In this work, a new class of black hole solutions in dilaton gravity has been obtained where the dilaton field is coupled with nonlinear Maxwell invariant as a source. The background space–time in this works is considered as the [Formula: see text]-dimensional toroidal metric. In the presence of the dilaton field (for some unique values of [Formula: see text][Formula: see text] a ), the electric field increases as we got farther away from the origin. In the absence of the dilaton field [Formula: see text], the electric field always decreases as one goes farther away from the origin. In the thermodynamical analysis, we obtain the Smarr formula for our solution. We find that the presence of the dilaton field makes the solutions to be locally stable near the origin. Also, this field vanishes the global stability near the origin compared to the no dilaton field case [Formula: see text]. We can say that the dilaton field has a crucial impact on the thermodynamical stability and it is a key factor in stability analysis. We study the quasinormal modes (QNMs) of black hole solutions in dilaton gravity. For this purpose, we use the WKB approximation method upto first order corrections. We have shown the perturbations decay in corresponding diagrams when the dilaton parameter [Formula: see text] and coupling constant [Formula: see text] change. Motivated by the thermodynamical analogy of black holes and Van der Waals liquid/gas systems, in this work, we investigate PV criticality of the obtained solution. We extend the phase space by considering the cosmological constant as thermodynamic pressure. We obtain the equation of state (EOS) and plot the relevant PV [Formula: see text] diagrams. We also present a class of interior solutions corresponding to the exterior solution in dilaton gravity. The solution which is obtained for a linear equation of state is regular and well-behaved at the stellar interior. a Dilaton field representation.

Modified BTZ black hole and some thermodynamical properties in dilaton/scalar gravity model

We construct a new class of black hole solutions of Einstein’s gravity in the presence of dilaton/scalar fields. In this regard, we present a general action (Eq. (1) in the introduction) where Einstein’s gravity is coupled with these fields. Using this action, we derive the equations of motion. Moreover, we employ n-dimensional static toroidal space-time as the background geometry. Our study reveals that the standard BTZ solution can be recovered from some of these solutions as a special case. We point out that the asymptotic behavior of the obtained solutions is neither asymptotically flat nor (A)dS ((anti-) de Sitter). We also show under which conditions these solutions behave (A)dS, asymptotically. Some basic thermodynamics of the black hole solution is also analyzed. The most important result derived from our study is that the presence of the dilaton field increases the tendency of temperature to be positive near the origin. Besides, when we investigate the black hole’s stability, it is shown that the presence of this field makes the solutions to be more stable near the origin.

Spicing up the recipe for echoes from exotic compact objects: Orbital differences and corrections in rotating backgrounds

Recently, it has been argued that near-horizon modifications of the standard (classical) black hole spacetime could lead to observable alterations of the gravitational waveform generated by a binary black hole coalescence. Such modifications can be inspired by quantum gravity considerations, resulting in speculative horizonless exotic compact objects (ECOs) with no singularities, which may be an alternative to the classical black hole solution. A largely model-independent description of these objects proposed in the literature relies on the introduction of a partially reflective wall at some small distance away from the ``would-be'' horizon. The inspiral-merger ringdown of a pair of such objects would be subject to possibly detectable deviations from the black hole case due to matter effects. In particular, the ringdown phase would be modified by the late emergence of so-called ``echoes'' in the waveform, but most studies so far have considered spherically symmetric backgrounds. We use an in-falling scalar charge as an initial perturbation to simulate the excitation of the echoes of a rotating ECO, and we explore both the corotating and counterrotating cases, which provide distinct signals. In particular, rotation breaks the symmetry between positive and negative frequencies and introduces a subdominant frequency contribution in each echo, which we examine here for the first time. Our results follow consistently from the solution of the Teukolsky equation using the MST method developed by Mano, Suzuki, and Takasugi and the construction of the complex Green's function integrated over different particle geodesics.

Does black hole continuum spectrum signal f(R) gravity in higher dimensions?

Extra dimensions, which led to the foundation and inception of string theory, provide an elegant approach to force-unification. With bulk curvature as high as the Planck scale, higher curvature terms, namely f(R) gravity seems to be a natural addendum in the bulk action. These can not only pass the classic tests of general relativity but also serve as potential alternatives to dark matter and dark energy. With interesting implications in inflationary cosmology, gravitational waves and particle phenomenology it is worth exploring the impact of extra dimensions and f(R) gravity in black hole accretion. Various classes of black hole solutions have been derived which bear non-trivial imprints of these ultraviolet corrections to general relativity. This in turn gets engraved in the continuum spectrum emitted by the accretion disk around black holes. Since the near horizon regime of supermassive black holes manifest maximum curvature effects, we compare the theoretical estimates of disk luminosity with quasar optical data to discern the effect of the modified background on the spectrum. In particular, we explore a certain class of black hole solution bearing a striking resemblance with the well-known Reissner Nordstrom de Sitter/anti-de Sitter/flat spacetime which unlike general relativity can also accommodate a negative charge parameter. By computing error estimators like chi-square, Nash-Sutcliffe efficiency, index of agreement, etc. we infer that optical observations of quasars favor a negative charge parameter which can be a possible indicator of extra dimensions. The analysis also supports an asymptotically de Sitter spacetime with an estimate of the magnitude of the cosmological constant whose origin is solely attributed to f(R) gravity in higher dimensions.

Charged black holes with axionic-type couplings: Classes of solutions and dynamical scalarization

We consider an augmented Einstein-Maxwell-scalar model including an axionic-type coupling between the scalar and electromagnetic field. We study dyonic black hole solutions in this model. For the canonical axionic coupling emerging from high energy physics, all charged black holes have axion hair. We present their domain of existence and investigate some physical properties. For other axionic-type couplings, two classes of black hole solutions may coexist in the model: scalar-free Reissner-Nordstr\"om black holes and scalarized black holes. We show that in some region of the parameter space the scalar-free solutions are unstable. Then, there is nonuniqueness since new scalarized black hole solutions with the same global charges, which are entropically preferred over the scalar-free solutions and, moreover, emerge dynamically from the instability of the former, also exist.

Thermal stability of a special class of black hole solutions in F(R) gravity

In this paper, we work on the topological Lifshitz-like black hole solutions of a special class of vacuum F(R)-gravity that are static and spherically symmetric. We investigate geometric and thermodynamic properties of the solutions with due respect to the validity of the first law of thermodynamics. We examine the van der Waals like behavior for asymptotically AdS solutions with spherical horizon by studying the P-v, G-T and C_{Q,P}-r_{+} diagrams and find a consistent result. We also investigate the same behavior for hyperbolic horizon and interestingly find that the system under study can experience a phase transition with negative temperature.