1,898 research outputs found
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 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 ().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
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