Object Picture of Electromagnetic Quasinormal Ringing for a Stringy Black Hole

We investigate the evolution of an electromagnetic field in the spacetime of a stringy black hole. The object picture of the quasinormal ringing has been obtained by the finite difference method. Compared with a Schwarzschild black hole, the results show that the electromagnetic field damps more slowly for a stringy black hole.     

Quasinormal Modes of a Black Hole with Quintessence-Like Matter and a Deficit Solid Angle for Electromagnetic Perturbation

We investigate the electromagnetic perturbation around a black hole with quintessence-like matter and a deficit solid angle. The complex frequencies of the quasinormal modes of electromagnetic perturbation are evaluated by the third-order WKB approximation. The results show that the electromagnetic perturbation around the black hole damps more slowly owing to the presence of the quintessence-like. The phenomenon can be distinguished from the black hole only with a deficit angle.     

Quasinormal Modes of Spherically Symmetric Curve Spacetime with Dark Matter Term

We study quasinormal modes of scalar field perturbation and electromagnetic field perturbation in a black hole space-time with dark matter by using WKB approximation method. The result shows clearly that the real part of black hole quasinormal modes is mainly determined by angular quantum number while its imaginary part mainly determined by model number. We also found out that the dark matter will restrain the perturbation frequency and slow down the speed of damping in spacetime. In addition; dark matter has a greater influence upon quasinormal modes in the electromagnetic field than that in the scalar field.     

Quasinormal Modes for Electromagnetic Field Perturbation of the Asymptotic Safe Black Hole

In this paper, the quasinormal modes (QNMs) of electromagnetic field perturbation to asymptotic safe (AS) black hole are discussed. Through six-order WKB approach we investigate the effects of quantum correction to the quasinormal modes (QNMs) numerically. Meanwhile by means of finite difference method, the evolutions of such perturbation to the safe black hole are figured out with corresponding parameters. It is found that the stability of black hole remains although the decay frequency and damping speed of oscillations are respectively increased and lowered by the quantum correction to classic Schwarzschild black hole.     

Evaporation of microscopic black holes in string theory and the bound on species

We address the question how string compactifications with D‐branes are consistent with the black hole bound, which arises in any theory with number of particle species to which the black holes can evaporate. For the Kaluza‐Klein particles, both longitudinal and transversal to the D‐branes, it is relatively easy to see that the black hole bound is saturated, and the geometric relations can be understood in the language of species‐counting. We next address the question of the black hole evaporation into the higher string states and discover, that contrary to the naive intuition, the exponentially growing number of Regge states does not preclude the existence of semi‐classical black holes of sub‐stringy size. Our analysis indicates that the effective number of string resonances to which such micro black holes evaporate is not exponentially large but is bounded by N = 1/g_s², which suggests the interpretation of the well‐known relation between the Planck and string scales as the saturation of the black hole bound on the species number. In addition, we also discuss some other issues in D‐brane compactifications with a low string scale of order TeV, such as the masses of light moduli fields.     

Negative mode of Schwarzschild black hole from the thermodynamic instability

The thermodynamic instability, for example the negative heat capacity, of a black hole implies the existence of off-shell negative mode(s) (unstable perturbation(s)) around the black hole geometry in the Euclidean path integral formalism of quantum gravity. We explicitly construct an off-shell unstable perturbation inspired from the negative heat capacity in the case of Schwarzschild black hole with/without a cosmological constant. We carefully check the boundary conditions, i.e. the regularity at the horizon, the traceless condition, and the normalizability.     

Effect of nonlinear electrodynamics on shadows of slowly rotating black holes

In this study, we investigate the effect of nonlinear electrodynamics on the shadows of charged, slowly rotating black holes with the presence of a cosmological constant. Rather than the null geodesic of the background black hole spacetime, the trajectory of a photon, as a perturbation of the nonlinear electrodynamic field, is governed by an effective metric. The latter can be derived by analyzing the propagation of a discontinuity of the electromagnetic waveform. Subsequently, the image of the black hole and its shadow can be evaluated using the backward ray-tracing technique. We explore the properties of the resultant black hole shadows of two different scenarios of nonlinear electrodynamics, namely, the logarithmic and exponential forms. In particular, the effects of nonlinear electrodynamics on the optical image are investigated, as well as the image's dependence on other metric parameters, such as the black hole spin and charge. The resulting black hole image and shadow display rich features that potentially lead to observational implications.     

On Clifford Space Relativity,Black Hole Entropy,Rainbow Metrics,Generalized Dispersion and Uncertainty Relations

An analysis of some of the applications of Clifford space relativity to the physics behind the modified black hole entropy-area relations, rainbow metrics, generalized dispersion and minimal length stringy uncertainty relations is presented.     

Quasinormal Modes in Double-Charge de Sitter Black Hole

The black hole, as a hot topic to be regarded as a normally research to become a strong evidence for its existence, made more and more people get involved in its research. To calculating the quasinormal modes for massless scalar field and Maxwell’s field in double-charge de Sitter black hole by using WKB approximation method, there is a fact that the speed of weakening electromagnetic perturbation will be reduced. The quasinormal modes in black hole mainly depends on angular quantum number l when its real part is in lower-frequency circumstances. At the same time, imaginary part mainly depends on the overtone number n. When the black hole carries the same electronic quantity, the more the electronic charges have, the smaller the real part and imaginary part of quasinormal modes will be.     

The membrane picture of Hawking radiation

The effect of a black hole on the classical physics of exterior electromagnetic fields can be expressed by replacing the black hole by a conducting membrane. We show that when we introduce quantum mechanics the currents in this membrane must also satisfy a quantum Langevin equation and that this, together with the nonzero transmission coefficient for the potential barrier around the hole in the membrane picture, gives rise to the Hawking radiation.     

The Generalized Stefan-Boltzmann Law of Slowly Changing Kerr-Newman Black Hole

Using the entropy density near the event horizon of Kerr-Newman black hole, the instantaneous radiation energy flux and the instantaneous radiation power of the slowly changing Kerr-Newman black hole have been studied. It is found that the thermal radiation of the Kerr-Newman black hole always satisfies the generalized Stefan-Boltzmann law and is affected by the gravitational field, the electromagnetic field around the black hole and the change of black hole event horizon. But the rate of the change of the event horizon usually makes very little affect on the instantaneous radiation energy flux and radiation power. Only when the rate of the change of the event horizon approaches to the light speed, it can make obviously affect on them.     

Restudy of the stability problem of the Schwarzschild black hole

The stability of the Schwarzschild black hole is restudied in the Painlevé coordinates. Using the Painlevé time coordinate to define the initial time, we reconsider the odd perturbation and find that the Schwarzschild black hole in the Painlevé coordinates is unstable. The Painlevé metric in this paper corresponds to the white-hole-connected region of the Schwarzschild black hole (r>2m) and the odd perturbation may be regarded as the angular perturbation. Therefore, the white-hole-connected region of the Schwarzschild black hole is unstable with respect to the rotating perturbation.     

Quasinormal Modes of the Schwarzschild Black Hole Surrounded by the Quintessence Field in Rastall Gravity

The quasinormal modes of the Schwarzschild black hole surrounded by the quintessence in Rastall gravity are studied using the sixth-order Wentzel-Kramers-Brillouin approximative approach. The effect of the Rastall parameter on the quasinormal modes of gravitational, electromagnetic and massless scalar perturbations is explored. Compared to the case of Einstein gravity, it is found that, when η < 0, the gravitational field, electromagnetic field as well as massless scalar field damp more rapidly and have larger real frequency of oscillation in Rastall gravity, while when η > 0, the gravitational field, electromagnetic field as well as massless scalar field damp more slowly and have smaller real frequency of oscillation in Rastall gravity. It is also found that the gravitational field, electromagnetic field as well as massless scalar field damp more and more slowly and the real frequency of oscillation for the gravitational perturbation, electromagnetic perturbation as well as massless scalar perturbation becomes smaller and smaller as the Rastall parameter η increases. Compared among the quasinormal frequencies of gravitational, electromagnetic and massless scalar perturbations, I find that, for fixed η, (l, n), ∈ and N_q, the oscillation damps most slowly for the gravitational perturbation, mediate for the electromagnetic perturbation and most rapidly for the massless scalar perturbation, and the real frequency of oscillation is the smallest for the gravitational perturbation, mediate for the electromagnetic perturbation and the largest for the massless scalar perturbation in Rastall gravity.     

Wave dynamics of a six-dimensional black hole localized on a tensional three-brane

We study the quasinormal modes and the late-time tail behavior of scalar perturbation in the background of a black hole localized on a tensional three-brane in a world with two large extra dimensions. We find that finite brane tension modifies the standard results in the wave dynamics for the case of a black hole on a brane with completely negligible tension. We argue that the wave dynamics contains the imprint of the extra dimensions.     

Evolution of electromagnetic waves of a point source in the Schwarzschild field

The problem of electromagnetic radiation of a source in the gravity field of a nearby black hole is considered. A complete class of exact axial-symmetric solutions of the eikonal equations is found. The components of the field tensor are obtained in the large frequency approximation. An expression is found for the strength of the observed radiation as a function of the distance between the black hole and the source, and of the angle between the directions black hole-observer and black hole-source. It is shown that the system consisting of a black hole and a normal star in rotation around the common center of gravity must look like an object of variable brightness.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 83–88, October, 1988.     

Charged black holes in the infinite derivative theory of gravity

The infinite derivative theory of gravity is a generalization of Einstein gravity with many interesting properties,but the black hole solutions in this theory are still not fully understood.In the paper,we concentrate on studying the charged black holes in such a theory.Adding the electromagnetic field part to the effective action,we show how the black hole solutions around the Reissner-Nordstrom metric can be solved perturbatively and iteratively.We further calculate the corresponding temperature,entropy and electrostatic potential of the black holes and verify the first law of thermodynamics.     

Quasinormal modes from potentials surrounding the?charged-dilaton black hole

We clarify the purely imaginary quasinormal frequencies of a massless scalar perturbation on 3D charged-dilaton black holes. This case is quite interesting, because the step of the potential appears outside the event horizon, similar to the case of the electromagnetic perturbations on large Schwarzschild–anti-de Sitter (AdS) black holes. It turns out that the potential-step type with a massless scalar perturbation provides purely imaginary quasinormal frequencies.     

Plunge waveforms from inspiralling binary black holes

We study the coalescence of nonspinning binary black holes from near the innermost stable circular orbit down to the final single rotating black hole. We use a technique that combines the full numerical approach to solve the Einstein equations, applied in the truly nonlinear regime, and linearized perturbation theory around the final distorted single black hole at later times. We compute the plunge waveforms, which present a non-negligible signal lasting for t approximately 100M showing early nonlinear ringing, and we obtain estimates for the total gravitational energy and angular momentum radiated.     

Spectrum of relativistic radiation from electric charges and dipoles as they fall freely into a black hole

The motion of electric charges and dipoles falling radially and freely into a Schwarzschild black hole is considered. The inverse effect of the electromagnetic fields on the black hole is neglected. Since the dipole is assumed to be a point particle, the deformation due to the action of tidal forces on it is neglected. According to the theorem stating that “black holes have no hair”, the multipole electromagnetic fields should be completely radiated as a multipole falls into a black hole. The electromagnetic radiation power spectrum for these multipoles (a monopole and a dipole) has been found. Differences have been found in the spectra for different orientations of the falling dipole. A general method has been developed to find the radiated multipole electromagnetic fields for multipoles (including higher-order multipoles—quadrupoles, etc.) falling freely into a black hole. The calculated electromagnetic spectra can be compared with observational data from stellar-mass and smaller black holes.