We investigate a model of a ringed accretion disk, made up by several rings rotating around a supermassive Kerr black hole attractor. Each toroid of the ringed disk is governed by the general relativity hydrodynamic Boyer condition of equilibrium configurations of rotating perfect fluids. Properties of the tori can then be determined by an appropriately defined effective potential reflecting the background Kerr geometry and the centrifugal effects. The ringed disks could be created in various regimes during the evolution of matter configurations around supermassive black holes. Therefore, both corotating and counterrotating rings have to be considered as being a constituent of the ringed disk. We provide constraints on the model parameters for the existence and stability of various ringed configurations and discuss occurrence of accretion onto the Kerr black hole and possible launching of jets from the ringed disk. We demonstrate that various ringed disks can be characterized by a maximum number of rings. We present also a perturbation analysis based on evolution of the oscillating components of the ringed disk. The dynamics of the unstable phases of the ringed disk evolution seems to be promising in relation to high-energy phenomena demonstrated in active galactic nuclei.
Read More
Possible astrophysical consequences of the Hořava quantum gravity
theory have been recently studied by several authors. They usually
employ the Kehagias-Sfetsos (KS) spacetime which is a spherically
symmetric vacuum solution of a specific version of Hořava's
gravity. The KS metric has several unusual geometrical properties that
in the present article we examine by means of the often used technique
of embedding diagrams. We pay particular attention to the transition
between naked singularity and black-hole states, which is possible along
some particular sequences of the KS metrics.
Read More
We have studied the orbits of magnetized particles around
Hořava-Lifshitz black hole with mass M immersed in an
asymptotically uniform magnetic field in the infrared approximation when
ω M2≫ 1. It is shown that magnetized particle's
orbit in Hořava-Lifshitz spacetime is different with compare to
one in Schwarzschild spacetime due to the presence of additional terms
related to the Kehagias-Sfetsos (KS) parameter ω. Using the
Hamilton-Jacobi formalism, we have found the dependence of the area of
stable circular orbits of the magnetized particle on dimensionless KS
parameter tilde{ω} and have plotted them for several values of
magnetic coupling parameter β as well as obtained the equations of
motion of the magnetized particle. Moreover, we have studied the
dependence of the collision of (magnetized, charged, non-charged)
particles on KS parameter ω for some fixed values of the magnetic
coupling parameter β.
Read More
Possible astrophysical consequences of the Hořava quantum gravity theory have been recently studied by several authors. They usually employ the Kehagias-Sfetsos (KS) spacetime which is a spherically symmetric vacuum solution of a specific version of Hořava's gravity. The KS metric has several unusual geometrical properties that in the present article we examine by means of the often used technique of embedding diagrams. We pay particular attention to the transition between naked singularity and black-hole states, which is possible along some particular sequences of the KS metrics.
Read More
We have studied the orbits of magnetized particles around Hořava-Lifshitz black hole with mass M immersed in an asymptotically uniform magnetic field in the infrared approximation when ω M2≫ 1. It is shown that magnetized particle's orbit in Hořava-Lifshitz spacetime is different with compare to one in Schwarzschild spacetime due to the presence of additional terms related to the Kehagias-Sfetsos (KS) parameter ω. Using the Hamilton-Jacobi formalism, we have found the dependence of the area of stable circular orbits of the magnetized particle on dimensionless KS parameter tilde{ω} and have plotted them for several values of magnetic coupling parameter β as well as obtained the equations of motion of the magnetized particle. Moreover, we have studied the dependence of the collision of (magnetized, charged, non-charged) particles on KS parameter ω for some fixed values of the magnetic coupling parameter β.
Read More
We construct perfect fluid tori in the field of the Kehagias-Sfetsos
(K-S) naked singularities. These are spherically symmetric vacuum
solutions of the modified Hořava quantum gravity, characterized
by a dimensionless parameter ω M^2, combining the gravitational
mass parameter M of the spacetime with the Hořava parameter
ω reflecting the role of the quantum corrections. In dependence on
the value of ω M^2, the K-S naked singularities demonstrate a
variety of qualitatively different behavior of their circular geodesics
that is fully reflected in the properties of the toroidal structures,
demonstrating clear distinction to the properties of the torii in the
Schwarzschild spacetimes. In all of the K-S naked singularity spacetimes
the tori are located above an "antigravity" sphere where matter can stay
in a stable equilibrium position, which is relevant for the stability of
the orbiting fluid toroidal accretion structures. The signature of the
K-S naked singularity is given by the properties of marginally stable
tori orbiting with the uniform distribution of the specific angular
momentum of the fluid, l= const. In the K-S naked singularity spacetimes
with ω M^2 > 0.2811, doubled tori with the same l= const can
exist; mass transfer between the outer torus and the inner one is
possible under appropriate conditions, while only outflow to the outer
space is allowed in complementary conditions. In the K-S spacetimes with
ω M^2 < 0.2811, accretion from cusped perfect fluid tori is not
possible due to the non-existence of unstable circular geodesics.
Read More
We construct perfect fluid tori in the field of the Kehagias-Sfetsos (K-S) naked singularities. These are spherically symmetric vacuum solutions of the modified Hořava quantum gravity, characterized by a dimensionless parameter ω M^2, combining the gravitational mass parameter M of the spacetime with the Hořava parameter ω reflecting the role of the quantum corrections. In dependence on the value of ω M^2, the K-S naked singularities demonstrate a variety of qualitatively different behavior of their circular geodesics that is fully reflected in the properties of the toroidal structures, demonstrating clear distinction to the properties of the torii in the Schwarzschild spacetimes. In all of the K-S naked singularity spacetimes the tori are located above an "antigravity" sphere where matter can stay in a stable equilibrium position, which is relevant for the stability of the orbiting fluid toroidal accretion structures. The signature of the K-S naked singularity is given by the properties of marginally stable tori orbiting with the uniform distribution of the specific angular momentum of the fluid, l= const. In the K-S naked singularity spacetimes with ω M^2 > 0.2811, doubled tori with the same l= const can exist; mass transfer between the outer torus and the inner one is possible under appropriate conditions, while only outflow to the outer space is allowed in complementary conditions. In the K-S spacetimes with ω M^2 < 0.2811, accretion from cusped perfect fluid tori is not possible due to the non-existence of unstable circular geodesics.
Read More
We apply the relativistic precession (RP) model with its variants and
the resonance epicyclic model with its variants, based on the
frequencies of the geodesic epicyclic motion in the field of a Kerr
black hole, to put limits on the mass of the black hole in the
ultraluminous X-ray source M82 X-1 demonstrating twin high-frequency
quasi-periodic oscillations (HF QPOs) with the frequency ratio near 3:2.
The mass limits implied by the geodesic HF QPO models are compared to
those obtained due to the model of string loop oscillations around a
stable equilibrium position. Assuming the whole range of the black hole
dimensionless spin, 0 < a < 1, the restrictions on the black hole
mass related to the twin HF QPOs are widely extended and strongly model
dependent; nevertheless, they give the lower limit M_{M82 X-1} > 130
M_{⊙} confirming existence of an intermediate black hole in the M82
X-1 source. The upper limit given by one of the variants of the geodesic
twin HF QPO models goes up to M_{M82 X-1}<1500 M_{⊙}. The range
37-210 mHz of the low-frequency QPOs observed in the M82 X-1 source
introduces additional restrictive limits on the black hole mass, if we
model the low-frequency QPOs by nodal precession of the epicyclic
motion. The nodal precession model restrictions combined with those
implied by the geodesic models of the twin HF QPOs give allowed ranges
of the M82 X-1 black hole parameters, namely 140 M_{⊙}<M_{M82
X-1}<660 M_{⊙} for the mass parameter and 0.05<a_{M82
X-1}<0.6 for the spin parameter.
Read More
We present results of our study of charged-fluid toroidal structures
surrounding a non-rotating black hole surrounded by a dipole and
large-scale, asymptotically uniform magnetic fields. In continuation of
our former study of electrically charged matter in approximation of zero
conductivity, we demonstrate the existence of orbiting structures in the
equatorial plane, levitating above it and those hovering near the
symmetry axis. We constrain the range of black-hole, magnetic fields and
matter parameters that allow stable configurations of the fluid
structures and derive the geometrical shape of equi-pressure surfaces,
characterizing the temperature and other astrophysical characteristic
profiles. 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, being
thus important in some astrophysical situations.
Read More
We study physical processes around a rotating black hole in pure
Gauss-Bonnet (GB) gravity. In pure GB gravity, the gravitational
potential has a slower fall-off as compared to the corresponding
Einstein potential in the same dimension. It is therefore expected that
the energetics of a pure GB black hole would be weaker, and our analysis
bears out that the efficiency of energy extraction by the Penroseprocess
is increased to 25.8 % and the particle acceleration is increased to
55.28 %; the optical shadow of the black hole is decreased. These are in
principle distinguishing observable features of a pure GB black hole.
Read More
