Extraction Energy From Charged Vaidya Black Hole Via Penrose Process

In this paper, we consider the analogy of the Penrose process in Charged Vaidya spacetime. We calculate the border of the generalized ergosphere, in which the charged particles with negative energy might exist, and show that it is temporary. We show that there are no closed orbits for particles with negative energy inside the generalized ergosphere. We investigate the question about the efficiency of the Penrose process and show that one can't extract large energies from a black hole.Comment: 10 pages, submitted to Chinese Physics

The structure of the generalized Vaidya spacetime containing the eternal naked singularity

In this paper the structure of the generalized Vaidya spacetime when the type-II of the matter field satisfies the equation of the state $P=\rho$ is investigated. Satisfying all energy conditions we show that this spacetime contains the 'eternal' naked singularity. It means that once the singularity is formed it will never be covered with the apparent horizon. However, in the case of the apparent horizon formation the resulting object is a white hole. We also prove that this spacetime contains only null naked singularity.Comment: 10 page

The influence of the charge on a dynamical photon sphere

In this paper, we consider the analytical model of a dynamical photon sphere described by charged Vaidya spacetime. By using the homothetic Killing vector, We transform the metric to the conformally static coordinates in which an extra conserved quantity exists along null trajectories which allows us to reduce the geodesic motion equations to the first-order differential equations. We compare the radius of a photon sphere with one in uncharged Vaidya spacetime and find that a charge always decreases the radius of a photon sphere.Comment: 18 page

The Negative Energy in Generalized Vaidya Spacetime

In this paper we consider the negative energy problem in generalized Vaidya spacetime. We consider several models when we have the naked singularity as a result of the gravitational collapse. In these models we investigate the geodesics for particles with negative energy when the II type of the matter field satisfies the equation of the state $P=\alpha \rho$ ($\alpha \in [0\,, 1]$).Comment: 18 page

On the particle collisions during gravitational collapse of Vaidya spacetimes

The center-of-mass energy can be arbitrarily high in Schwarzschild spacetime if one considers the front collision of two particles, one of which moves along so-called white hole geodesics and another one along a black hole geodesic. This process can take place if one considers the gravitational collapse model. In this paper, we consider the well-known naked singularity formation in Vaidya spacetime and investigate the question about two particle collision near the boundary of the collapsing cloud. The center-of-mass energy of the front collision is considered. One particle moves away from the naked singularity and another one falls onto a collapsing cloud. We show that the center-of-mass energy grows unboundly if the collision takes place in the vicinity of the conformal Killing horizon.Comment: 11 pages, corrected versio

Geodesics for particles with negative energy in Kerr's metric

According to Penrose effect, particles with negative energy can exist in the ergospheres of rotating black holes. We analyze geodesics for such particles and show that there are no circular and elliptic orbits in the ergosphere of a rotating black hole. We also show that there are geodesics which begin and terminate at the singularity and present the conditions under which such geodesics do not begin and terminate at the singularity.Comment: 8 page

On particle collisions in the vicinity of the charged black holes

The process of particle collision in the vicinity of black holes is known to generate unbounded energies in the center-of-mass frame (the Banados-Silk-West (BSW) effect) under specific conditions. We consider this process in the charged black hole metrics, namely, the Reissner-Nordstrom (RN) and Majumdar-Papapetrou (MP) metrics. We consider the energy extraction from Bardeen regular black hole due to BSW effect. Like in RN case, we show that there is no restriction on energy extraction, but for real charged particles this effect is negligible. We derive necessary and sufficient conditions for this process. The conditions for the BSW effect in RN and MP metrics are shown to be identical, which is explained by the asymptotic equivalence of the two metrics near the horizons. Energy extraction in the RN metric is discussed. It is shown that if two real particles collide while falling onto a black hole, they are extremely unlikely to generate an ultra-massive particle. For the case of head-on collisions, we derive an upper bound on extracted mass, which depends on the lapse function of the metric at the point of collision.Comment: 10 pages, accepted to Gravitation and Cosmolog

Hairy Kiselev Black Hole Solutions

In the realm of astrophysics, black holes exist within nonvacuum cosmological backgrounds, making it crucial to investigate how these backgrounds influence the properties of black holes. In this work, we first introduce a novel static spherically-symmetric exact solution of Einstein field equations representing a surrounded hairy black hole. This solution represents a generalization of the hairy Schwarzschild solution recently derived using the extended gravitational decoupling method. Then, we discuss how the new induced modification terms attributed to the primary hairs and various background fields affect the geodesic motion in comparison to the conventional Schwarzschild case. Although these modifications may appear insignificant in most cases, we identify specific conditions where they can be comparable to the Schwarzschild case for some particular background fields.Comment: 25 pages, 9 figure

Generation of the Super Small-Scale Artificial Ionospheric Irregularities in the Ionosphere Pumped by High-Power HF Radio Waves

© 2017, Springer Science+Business Media, LLC, part of Springer Nature. We present the results of experimental studies of generation of super small-scale plasma-density irregularities in the ionospheric F 2 region pumped by a high-power HF O-mode wave at frequencies close to the fourth gyroharmonic in the region of its interaction with the plasma. The experiments were performed using the Sura heating facility. The super small-scale irregularities were sounded by GPS satellite signals. It has been shown that super small-scale irregularities are excited with the most efficiency in the region of the magnetic zenith for the pump wave. The intensity of such irregularities and typical times of their development and decay are determined