Hot plasma waves in Veselago medium around Reissner-Nordström black hole

We investigate the general relativistic magnetohydronadynamic (GRMHD) equations for hot plasmas in a Veselago medium around the Reissner-Nordström (RN) black hole. Using the 3+1 formalisms of spacetime, we write the GRMHD equations and perturb them linearly. These are then Fourier analyzed for the magnetized and nonmagnetized plasmas in rotating and nonrotating backgrounds. We derive dispersion relations and analyze the wave properties by the graphs of wave vector, refractive index and change in refractive. The results confirm the presence of Veselago medium for rotating magnetized/nonmagnetized and nonrotating nonmagnetized plasmas.     

Tunneling of massive and charged particles from noncommutative Reissner-Nordström black hole

Massive charged and uncharged particles tunneling from commutative Reissner-Nordström black hole horizon has been studied with details in literature. Here, by adopting the coherent state picture of spacetime noncommutativity, we study tunneling of massive and charged particles from a noncommutative inspired Reissner-Nordström black hole horizon. We show that Hawking radiation in this case is not purely thermal and there are correlations between emitted modes. These correlations may provide a solution to the information loss problem. We also study thermodynamics of noncommutative horizon in this setup.     

An analysis of wave properties of isothermal plasma around Reissner-Nordström black hole

The 3+1 spacetime split is used in a preliminary investigation of waves propagating in a medium of isothermal plasma in the vicinity of event horizon of Reissner-Nordström planar analogue. The general relativistic magnetohydrodynamic equations for isothermal have been investigated there. The dispersion relations are obtained by using linear perturbation and Fourier analyze techniques for non-rotating and rotating, non-magnetized and magnetized environment. The wave number, phase velocity, group velocity etc. are shown to discuss the nature of the waves.     

Quasinormal modes and Hawking radiation of a Reissner-Nordström black hole surrounded by quintessence

We investigate quasinormal modes (QNMs) and Hawking radiation of a Reissner-Nordström black hole surrounded by quintessence. The Wentzel-Kramers-Brillouin (WKB) method is used to evaluate the QNMs and the rate of radiation. The results show that due to the interaction of the quintessence with the background metric, the QNMs of the black hole damp more slowly when increasing the density of quintessence and the black hole radiates at slower rate.     

Phase transition in the Reissner–Nordström black hole

The thermodynamics of the Reissner–Nordström black hole at the charge-to-mass ratio of \(\sqrt{3}/2\) is studied. We show that there exists infinite discontinuity not only in the heat capacity but also in the electromagnetic potential and hence in the Gibbs free energy. Despite the existence of an infinite discontinuity in the heat capacity, it is shown that there exists no phase transition in the Reissner–Nordström black hole. The discontinuity may be merely an artefact of the change in the slope of the |Q| vs. M curve when the charge-to-mass ratio crosses \(\sqrt{3}/2\). This may signify that the horizon temperature is not a well-behaved thermodynamic parameter in the black hole thermodynamics.     

Generalized uncertainty principle and quantum gravitational effects on tunneling rate of Reissner-Nordström black hole

It is shown that the Bekenstein-Hawking entropy of black holes can accept a correction that effects on the radiation tunneling probability. By assumption of a spatially flat universe accompanied with expansion of metric, we could obtain an expression for entropy of black hole that is changing with respect to time and Bekenstein-Hawking temperature.     

The generalized uncertainty principle and the quantum entropy due to spin fields on the Reissner-Nordström black hole background

By using the null tetrad and the ’t Hooft brick-wall model, the quantum entropies of a Reissner-Nordström black hole due to the Weyl neutrino, electromagnetic, massless Rarita-Schwinger and gravitational fields for the source-free case are investigated from a generalized uncertainty principle. The divergence structure for the entropy is demonstrated. In addition to the usual linearly and logarithmically divergent terms, additional quadratic, cubic, biquadratic and other higher order divergences exist near the event horizon in the entropy, which not only depend on the black hole characteristics but also on the spin fields and the gravitational interactions. The terms describe the contribution of the quantum fields to the entropy and the effects of the generalized uncertainty principle on it. If the smallest length scale is taken into account, the contribution of the gravitational interactions to the entropy is found to be a part of the dominant term and very important, and therefore it can not be neglected.     

Formation of black holes through BSW effect and black hole–black hole collisions

We study mechanism of formation of black holes (BHs) from collisions of particles in the vicinity of the supermassive black hole acting as a particle accelerator trough BSW (Banados-Silk-West) effect. Moreover, we also investigate BH-BH collision, in which stellar black holes colliding near the horizon of a rotating supermassive black hole can reach large values of the center-of-mass energy. This result implies that high arbitrary energy of collisions causes to be transformed into radiation energy and particles, which might bring possible visible signals through the astrophysical observations. We study the radiation energy from a collision of two accelerating stellar black holes and find a maximal value of the radiation energy to be nearly E _rad ≈2.5?10⁵⁶ erg for the ultrarelativistic value of v/c=0.99 from BH-BH collisions.     

Wormhole deformation of the Reissner-Nordstr?m spacetime

A radial deformation of the Reissner-Nordstr?m metric which leads to the appearance of charged, traversable wormholes is investigated. It is shown that the resulting wormholes are not covered by event horizons and physical signals can travel between the two parallel universes either way across the wormhole. The status of energy conditions and the classification of geodesics are also discussed in details.     

Hawking non-thermal and thermal radiations of Reissner Nordström anti-de Sitter black hole by Hamilton-Jacobi method

We have investigated Hawking non-thermal and purely thermal Radiations of Reissner Nordström anti-de Sitter (RNAdS) black hole by massive particles tunneling method. The spacetime background has taken as dynamical, incorporate the self-gravitation effect of the emitted particles the imaginary part of the action has derived from Hamilton-Jacobi equation. We have supposed that energy and angular momentum are conserved and have shown that the non-thermal and thermal tunneling rates are related to the change of Bekenstein-Hawking entropy and the derived emission spectrum deviates from the pure thermal spectrum. The results for RNAdS black hole is also in the same manner with Parikh and Wilczek’s opinion and explored the new result for Hawking radiation of RNAdS black hole.     

Entanglement entropy of acoustic black hole in Bose–Einstein condensate

We study the entanglement entropy associated to the phonons generated via the Hawking mechanism of acoustic black holes in a Bose–Einsten condensate. The lowest energy allowed for the radiated phonons is found to be a function of space coordinate. Based this, we calculate the entanglement entropy, which contains three parts: a leading term, which is a constant of value 1/6, a logarithmic correction term and some series terms. We discuss the convergence of the series terms.     

Does black hole spin play a key role in the FSRQ/BL Lac dichotomy?

Blazars are characterized by large intensity and spectral variations across the electromagnetic spectrum It is believed that jets emerging from them are almost aligned with the line-of-sight. The majority of identified extragalactic sources in γ-ray catalogs of EGRET and Fermi are blazars. Observationally,blazars can be divided into two classes: flat spectrum radio quasars(FSRQs) and BL Lacs. BL Lacs usually exhibit lower γ-ray luminosity and harder power law spectra at γ-ray energies than FSRQs. We attempt to explain the high energy properties of FSRQs and BL Lacs from Fermi γ-ray space telescope observations. It was argued previously that the difference in accretion rates is mainly responsible for the large mismatch in observed luminosity in γ-ray. However, when intrinsic luminosities are derived by correcting for beaming effects, this difference in γ-ray luminosity between the two classes is significantly reduced. In order to explain this difference in intrinsic luminosities, we propose that spin plays an important role in the luminosity distribution dichotomy of BL Lacs and FSRQs. As the outflow power of a blazar increases with increasing spin of a central black hole, we suggest that the spin plays a crucial role in making BL Lac sources low luminous and slow rotators compared to FSRQ sources.     

Dirac quasinormal modes of the deformed Hořava-Lifshitz black hole spacetime

Using the third-order WKB approximation, we evaluate the quasinormal frequencies of massless Dirac field perturbation around a deformed black hole in the Hořava-Lifshitz gravity with coupling constant λ=1. Our result shows that the Hořava-Lifshitz parameter α plays an important role for the quasinormal frequencies and we discuss the variation of quasinormal frequencies with α. Moreover, we find that the massless Dirac field perturbations decay more slowly in the deformed Hořava-Lifshitz gravity.     

Role of a tachyonic field in accelerating the Universe in the presence of a perfect fluid

Recently, a tachyonic field was presented as a dark energy model to represent the present acceleration of the Universe. In this paper, we consider a mixture of tachyonic fluid with a perfect fluid. For this purpose we consider barotropic fluid and Generalized Chaplygin gas (GCG). We present a particular form of the scale factor. We solve the equations of motion to get exact solutions of the density, tachyonic potential and the tachyonic field. We introduce a coupling term to show that the interaction decays with time. We also show that the nature of the potentials vary, so the interaction term reduces the potential in both cases.     

Shadow of rotating Hořava-Lifshitz black hole

The shadow of rotating Ho?ava-Lifshitz black hole has been studied and it was shown that in addition to the specific angular momentum a, parameters of Ho?ava-Lifshitz spacetime essentially deform the shape of the black hole shadow. For a given value of the black hole spin parameter a, the presence of a parameter Λ _W and KS parameter ω enlarges the shadow and reduces its deformation with respect to the one in the Kerr spacetime. We have found a dependence of radius of the shadow R _s and distortion parameter δ _s from parameter Λ _W and KS parameter ω both. Optical features of the rotating Ho?ava-Lifshitz black hole solutions are treated as emphasizing the rotation of the polarization vector along null congruences. A comparison of the obtained theoretical results on polarization angle with the observational data on Faraday rotation measurements provides the upper limit for the δ parameter as δ≤2.1?10^?3.     

What is the closest black hole to the Sun?

We examine the distance of the two galactic microquasars GRO J1655–40 and A 0620–00 which are potentially the two closest black holes to the Sun. We aim to provide a picture as wide and complete as possible of the problem of measuring the distance of microquasars in our Galaxy. The purpose of this work is to fairly and critically review in great detail every distance method used for these two microquasars in order to show that the distances of probably all microquasars in our Galaxy are much more uncertain than currently admitted. Moreover, we show that many confirmations of quantitative results are often entangled and rely on very uncertain measurements. We also present a new determination of the maximum distance of GRO J1655–40 using red clump giant stars, and show that it confirms our earlier result of a distance less than 2 kpc instead of 3.2 kpc. Because, it then becomes more likely that GRO J1655–40 could originate from the stellar cluster NGC 6242, located at 1.0 kpc, we review the distance estimations of A 0620–00, which is so far the closest black hole with an average distance of about 1.0 kpc. We show that the distance methods used for A 0620–00 are also problematic. Finally, we present a new analysis of spectroscopic and astrometric archival data on this microquasar, and apply the maximum distance method of Foellmi et al. [Foellmi, C., Depagne, E., Dall, T.H., Mirabel, I.F., 2006b. A&A 457, 249]. It appears that A 0620–00 could indeed be even closer to the Sun than currently estimated, and consequently would be the closest known black hole to the Sun.     

Verification of maximum limit of density variation parameter λ for a stable neutron star using Reissner-Nordström interior solution

A static spherically-symmetric model, based on an exact solution of Einstein's equation, gives the permissible matter density ~2 × 10¹⁴ g cm^–3. By use of the change in radius density (i.e., central density per unit radius) minimum, Parui and Sarma (1991) have estimated the upper limit of the density variation parameter = 0.68 for a superdense star such as a neutron star withK = –2. In this paper we have verified this upper limit using the Reissner-Nordström interior solution of the Einstein-Maxwell's field equations withK = - 3.