We study charged-fluid toroidal structures surrounding a nonrotating charged black hole immersed in a large-scale, asymptotically uniform magnetic field. In continuation of our former study on electrically charged matter in approximation of zero conductivity, we demonstrate the existence of orbiting structures in permanent rigid rotation in the equatorial plane and charged clouds hovering near the symmetry axis. We constrain the range of parameters that allow stable configurations and derive the geometrical shape of equipressure surfaces. Our simplified analytical study suggests that these regions of stability may be relevant for trapping electrically charged particles and dust grains in some areas of the black hole magnetosphere and thus important in some astrophysical situations.
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The Large Observatory For x-ray Timing (LOFT) was studied within ESA M3
Cosmic Vision framework and participated in the final downselection for
a launch slot in 2022-2024. Thanks to the unprecedented combination of
effective area and spectral resolution of its main instrument, LOFT will
study the behaviour of matter under extreme conditions, such as the
strong gravitational field in the innermost regions of accretion flows
close to black holes and neutron stars, and the supranuclear densities
in the interior of neutron stars. The science payload is based on a
Large Area Detector (LAD, 10 m2 effective area, 2-30 keV,
240 eV spectral resolution, 1° collimated field of view) and a Wide
Field Monitor (WFM, 2-50 keV, 4 steradian field of view, 1 arcmin source
location accuracy, 300 eV spectral resolution). The WFM is equipped with
an on-board system for bright events (e.g. GRB) localization. The
trigger time and position of these events are broadcast to the ground
within 30 s from discovery. In this paper we present the status of the
mission at the end of its Phase A study.
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We discuss photon and test-particle orbits in the Kehagias-Sfetsos (KS)
metric of Hořava's gravity. For any value of the Hořava
parameter ω, there are values of the gravitational mass M for
which the metric describes a naked singularity, and this is always
accompanied by a vacuum "antigravity sphere" on whose surface a test
particle can remain at rest (in a zero angular momentum geodesic), and
inside which no circular geodesics exist. The observational appearance
of an accreting KS naked singularity in a binary system would be that of
a quasistatic spherical fluid shell surrounded by an accretion disk,
whose properties depend on the value of M, but are always very different
from accretion disks familiar from the Kerr-metric solutions. The
properties of the corresponding circular orbits are qualitatively
similar to those of the Reissner-Nordström naked singularities.
When event horizons are present, the orbits outside the Kehagias-Sfetsos
black hole are qualitatively similar to those of the Schwarzschild
metric.
Read More
The Large Observatory For x-ray Timing (LOFT) was studied within ESA M3 Cosmic Vision framework and participated in the final downselection for a launch slot in 2022-2024. Thanks to the unprecedented combination of effective area and spectral resolution of its main instrument, LOFT will study the behaviour of matter under extreme conditions, such as the strong gravitational field in the innermost regions of accretion flows close to black holes and neutron stars, and the supranuclear densities in the interior of neutron stars. The science payload is based on a Large Area Detector (LAD, 10 m2 effective area, 2-30 keV, 240 eV spectral resolution, 1° collimated field of view) and a Wide Field Monitor (WFM, 2-50 keV, 4 steradian field of view, 1 arcmin source location accuracy, 300 eV spectral resolution). The WFM is equipped with an on-board system for bright events (e.g. GRB) localization. The trigger time and position of these events are broadcast to the ground within 30 s from discovery. In this paper we present the status of the mission at the end of its Phase A study.
Read More
We discuss photon and test-particle orbits in the Kehagias-Sfetsos (KS) metric of Hořava's gravity. For any value of the Hořava parameter ω, there are values of the gravitational mass M for which the metric describes a naked singularity, and this is always accompanied by a vacuum "antigravity sphere" on whose surface a test particle can remain at rest (in a zero angular momentum geodesic), and inside which no circular geodesics exist. The observational appearance of an accreting KS naked singularity in a binary system would be that of a quasistatic spherical fluid shell surrounded by an accretion disk, whose properties depend on the value of M, but are always very different from accretion disks familiar from the Kerr-metric solutions. The properties of the corresponding circular orbits are qualitatively similar to those of the Reissner-Nordström naked singularities. When event horizons are present, the orbits outside the Kehagias-Sfetsos black hole are qualitatively similar to those of the Schwarzschild metric.
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We demonstrate that ultra-high-energy collisions of particles falling
freely from rest at infinity can occur in the field of near-extreme
Kehagias-Sfetsos naked singularities related to the Hořava
gravity. However, the efficiency of escaping of created
ultrarelativistic particles and the energy efficiency of the collisional
process relative to distant observers are significantly lowered due to
large gravitational redshift, which is substantially lower in comparison
to those related to the collisions occurring close to the equatorial
plane of near-extreme Kerr naked-singularity spacetimes. In the
Kehagias-Sfetsos naked-singularity spacetimes, the energy efficiency
relative to distant observers corresponds to the covariant energy of the
colliding particles only. Finally, we demonstrate how the
ultra-high-energy collisions are modified for charged particles if the
Kehagias-Sfetsos naked singularities are immersed in a uniform magnetic
field.
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Based on the Newman-Janis algorithm, the Ayón-Beato-García
spacetime metric [Phys. Rev. Lett. 80, 5056 (1998)] of the regular
spherically symmetric, static, and charged black hole has been converted
into rotational form. It is shown that the derived solution for rotating
a regular black hole is regular and the critical value of the electric
charge for which two horizons merge into one sufficiently decreases in
the presence of the nonvanishing rotation parameter a of the black hole.
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Astrophysical plasmas in the surrounding of compact objects and subject
to intense gravitational and electromagnetic fields are believed to give
rise to relativistic regimes. Theoretical and observational evidences
suggest that magnetized plasmas of this type are collisionless and can
persist for long times (e.g., with respect to a distant observer,
coordinate, time), while exhibiting geometrical structures characterized
by the absence of well-defined spatial symmetries. In this paper, the
problem is posed whether such configurations can correspond to some kind
of kinetic equilibrium. The issue is addressed from a theoretical
perspective in the framework of a covariant Vlasov statistical
description, which relies on the method of invariants. For this purpose,
a systematic covariant variational formulation of gyrokinetic theory is
developed, which holds without requiring any symmetry condition on the
background fields. As a result, an asymptotic representation of the
relativistic particle magnetic moment is obtained from its formal exact
solution, in terms of a suitably defined invariant series expansion
parameter (perturbative representation). On such a basis, it is shown
that spatially non-symmetric kinetic equilibria can actually be
determined, an example being provided by Gaussian-like distributions. As
an application, the physical mechanisms related to the occurrence of a
non-vanishing equilibrium fluid 4-flow are investigated.
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We demonstrate that ultra-high-energy collisions of particles falling freely from rest at infinity can occur in the field of near-extreme Kehagias-Sfetsos naked singularities related to the Hořava gravity. However, the efficiency of escaping of created ultrarelativistic particles and the energy efficiency of the collisional process relative to distant observers are significantly lowered due to large gravitational redshift, which is substantially lower in comparison to those related to the collisions occurring close to the equatorial plane of near-extreme Kerr naked-singularity spacetimes. In the Kehagias-Sfetsos naked-singularity spacetimes, the energy efficiency relative to distant observers corresponds to the covariant energy of the colliding particles only. Finally, we demonstrate how the ultra-high-energy collisions are modified for charged particles if the Kehagias-Sfetsos naked singularities are immersed in a uniform magnetic field.
Read More
Based on the Newman-Janis algorithm, the Ayón-Beato-García spacetime metric [Phys. Rev. Lett. 80, 5056 (1998)] of the regular spherically symmetric, static, and charged black hole has been converted into rotational form. It is shown that the derived solution for rotating a regular black hole is regular and the critical value of the electric charge for which two horizons merge into one sufficiently decreases in the presence of the nonvanishing rotation parameter a of the black hole.
Read More
