Near a rotating black hole, circular motion of particles, dust grains and complex fluids have been investigated as a model for accretion of gaseous and dusty environment in the toroidal geometry. Here we further discuss, within the framework of general relativity, figures of equilibrium of matter under the influence of combined gravitational and large-scale magnetic fields, assuming that the accreted material acquires a small (but non-vanishing) electric charge due to the interplay of plasma processes and photoionization. We employ different solutions for the central body (magnetized Kerr metric, or a massive magnetic dipole) and we identify the corresponding regions of stability. The action of gravitational and electromagnetic forces jointly determine the regions of stable motion, in particular, whether the halo lobes develop where particles can be captured in permanent circulation around the central body. Therefore, our set-up is relevant in the context of accreting compact objects where the halo motion can describe the overall global motion through corona of an accretion disc or a geometrically thick torus. We also investigate situations when the motion exhibits the onset of chaos. In order to characterize the measure of chaoticness we employ techniques of Poincare surfaces of section and Recurrence plots. Acknowledgments: Czech-US collaboration project (ref. ME09036) and the Czech Science Foundation program (ref. P209/10/P190) are gratefully acknowledged for their continued support.
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Near a rotating black hole, circular motion of particles, dust grains
and complex fluids have been investigated as a model for accretion of
gaseous and dusty environment in the toroidal geometry. Here we further
discuss, within the framework of general relativity, figures of
equilibrium of matter under the influence of combined gravitational and
large-scale magnetic fields, assuming that the accreted material
acquires a small (but non-vanishing) electric charge due to the
interplay of plasma processes and photoionization. We employ different
solutions for the central body (magnetized Kerr metric, or a massive
magnetic dipole) and we identify the corresponding regions of stability.
The action of gravitational and electromagnetic forces jointly determine
the regions of stable motion, in particular, whether the halo lobes
develop where particles can be captured in permanent circulation around
the central body. Therefore, our set-up is relevant in the context of
accreting compact objects where the halo motion can describe the overall
global motion through corona of an accretion disc or a geometrically
thick torus. We also investigate situations when the motion exhibits the
onset of chaos. In order to characterize the measure of chaoticness we
employ techniques of Poincare surfaces of section and Recurrence plots.
Acknowledgments: Czech-US collaboration project (ref. ME09036) and the
Czech Science Foundation program (ref. P209/10/P190) are gratefully
acknowledged for their continued support.
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We test precision of the Cosmological Paczynski-Wiita (CPW) potential reflecting properties of the Schwarzschild-de Sitter (SdS) spacetimes in modeling dynamical phenomena related to galaxy motion. We consider a simplified model of Magellanic Clouds moving in the field of Milky Way as test particles. Time evolution of their position along trajectories obtained in the CPW framework using the notion of Newtonian time is compared to the one obtained in the fully general relativistic (GR) approach when the time evolution is expressed in terms of time related to the location of Earth in the Galaxy field. The differences in the position-evolution of the Magellanic Clouds obtained in the CPW and GR approaches are given for appropriately chosen values of the Milky Way mass. It is shown that the integrated relativistic corrections represent 10-5 part of the Newtonian CPW predictions for the orbital characteristics of the motion and slightly grow with Galaxy mass growing, being at least by one order higher than the local scaling GR corrections. The integrated orbital GR corrections thus could be important only in very precise modeling of the motion of Magellanic Clouds. The CPW framework is used to show that, quite surprisingly, the influence of the cosmological constant on the Magellanic Clouds motion can be strong and significantly alters the trajectories of Magellanic Clouds and time evolution along them. The relative contribution of the cosmological constant is 10-1 or higher. It is most profoundly demonstrated by the increase of the binding mass that represents 22% for Small Magellanic Cloud and even 47% for Large Magellanic Cloud, putting serious doubts on gravitational binding to the Milky Way in the later case.
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We test precision of the Cosmological Paczynski-Wiita (CPW) potential
reflecting properties of the Schwarzschild-de Sitter (SdS) spacetimes in
modeling dynamical phenomena related to galaxy motion. We consider a
simplified model of Magellanic Clouds moving in the field of Milky Way
as test particles. Time evolution of their position along trajectories
obtained in the CPW framework using the notion of Newtonian time is
compared to the one obtained in the fully general relativistic (GR)
approach when the time evolution is expressed in terms of time related
to the location of Earth in the Galaxy field. The differences in the
position-evolution of the Magellanic Clouds obtained in the CPW and GR
approaches are given for appropriately chosen values of the Milky Way
mass. It is shown that the integrated relativistic corrections represent
10-5 part of the Newtonian CPW predictions for the orbital
characteristics of the motion and slightly grow with Galaxy mass
growing, being at least by one order higher than the local scaling GR
corrections. The integrated orbital GR corrections thus could be
important only in very precise modeling of the motion of Magellanic
Clouds. The CPW framework is used to show that, quite surprisingly, the
influence of the cosmological constant on the Magellanic Clouds motion
can be strong and significantly alters the trajectories of Magellanic
Clouds and time evolution along them. The relative contribution of the
cosmological constant is 10-1 or higher. It is most
profoundly demonstrated by the increase of the binding mass that
represents 22% for Small Magellanic Cloud and even 47% for Large
Magellanic Cloud, putting serious doubts on gravitational binding to the
Milky Way in the later case.
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String theory indicates the existence of primordial Kerr superspinars, extremely compact objects with exterior described by the Kerr naked-singularity geometry. The primordial superspinars have to be converted to a black hole due to accretion, but they could survive to the era of high-redshift quasars. We discuss observational phenomena caused by the primordial Kerr superspinars in this era, considering the properties of corotating Keplerian accretion discs orbiting such superspinars and the optical phenomena modified by their presence. The potential well around a near-extreme superspinar with spin a very close to the extreme black hole value a = 1 is very deep so that the efficiency of the accretion process reaches 157.7%, influencing thus significantly the spectral continuum of corotating Keplerian discs and giving a signature of near-extreme superspinars. Such superspinars can also serve as an efficient accelerator for extremely high-energy collisions. Phenomena enabling a clear distinction of primordial Kerr superspinars and black holes are related to the disc oscillations with the radial and vertical epicyclic frequencies and the most profound could be differences implied by the profiled spectral lines generated in the innermost parts of the corotating Keplerian discs.
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We study non-geodesic corrections to the quasicircular motion of charged test particles in the field of magnetized slowly rotating neutron stars. The gravitational field is approximated by the Lense-Thirring geometry, and the magnetic field is of the standard dipole character. Using a fully relativistic approach, we determine the influence of the electromagnetic interaction (both attractive and repulsive) on the quasicircular motion. We focus on the behaviour of the orbital and epicyclic frequencies of the motion. Components of the four-velocity of the orbiting charged test particles are obtained by the numerical solution of equations of motion, and the epicyclic frequencies are obtained by using the standard perturbative method. The role of the combined effect of the neutron star magnetic field and its rotation in the character of the orbital and epicyclic frequencies is discussed. It is demonstrated that even in the Lense-Thirring spacetime, particles being static relative to distant observers can exist due to the combined gravo-electromagnetic interaction.
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We study acceleration of current-carrying string loops governed by the presence of an outer tension barrier and an inner angular momentum barrier in the field of Schwarzschild-de Sitter black holes. We restrict attention to the axisymmetric motion of string loops with energy high enough, when the string loop can overcome the gravitational attraction and escape to infinity. We demonstrate that string loops can be scattered near the black hole horizon, and the energy of string oscillations can be efficiently converted to the energy of their linear motion. Such a transmutation effect can potentially represent acceleration of jets in active galactic nuclei and microquasars. We give the conditions limiting energy available for conversion onto the jetlike motion. Surprisingly, we are able to show that string loops starting from rest can be accelerated up to velocities v∼c even in the field of Schwarzschild black holes, if their angular momentum parameter is low enough. Such loops could serve as an explanation of highly relativistic jets observed in some quasars and active galactic nuclei. The cosmic repulsion becomes important behind the so-called static radius where it accelerates the linear motion of the string loops up to velocity v=c that is reached at the cosmic horizon of the Schwarzschild-de Sitter spacetimes independently of the angular momentum parameter of the strings.
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String theory indicates the existence of primordial Kerr superspinars,
extremely compact objects with exterior described by the Kerr
naked-singularity geometry. The primordial superspinars have to be
converted to a black hole due to accretion, but they could survive to
the era of high-redshift quasars. We discuss observational phenomena
caused by the primordial Kerr superspinars in this era, considering the
properties of corotating Keplerian accretion discs orbiting such
superspinars and the optical phenomena modified by their presence. The
potential well around a near-extreme superspinar with spin a very close
to the extreme black hole value a = 1 is very deep so that the
efficiency of the accretion process reaches 157.7%, influencing thus
significantly the spectral continuum of corotating Keplerian discs and
giving a signature of near-extreme superspinars. Such superspinars can
also serve as an efficient accelerator for extremely high-energy
collisions. Phenomena enabling a clear distinction of primordial Kerr
superspinars and black holes are related to the disc oscillations with
the radial and vertical epicyclic frequencies and the most profound
could be differences implied by the profiled spectral lines generated in
the innermost parts of the corotating Keplerian discs.
Read More
We study non-geodesic corrections to the quasicircular motion of charged
test particles in the field of magnetized slowly rotating neutron stars.
The gravitational field is approximated by the Lense-Thirring geometry,
and the magnetic field is of the standard dipole character. Using a
fully relativistic approach, we determine the influence of the
electromagnetic interaction (both attractive and repulsive) on the
quasicircular motion. We focus on the behaviour of the orbital and
epicyclic frequencies of the motion. Components of the four-velocity of
the orbiting charged test particles are obtained by the numerical
solution of equations of motion, and the epicyclic frequencies are
obtained by using the standard perturbative method. The role of the
combined effect of the neutron star magnetic field and its rotation in
the character of the orbital and epicyclic frequencies is discussed. It
is demonstrated that even in the Lense-Thirring spacetime, particles
being static relative to distant observers can exist due to the combined
gravo-electromagnetic interaction.
Read More
We study acceleration of current-carrying string loops governed by the
presence of an outer tension barrier and an inner angular momentum
barrier in the field of Schwarzschild-de Sitter black holes. We restrict
attention to the axisymmetric motion of string loops with energy high
enough, when the string loop can overcome the gravitational attraction
and escape to infinity. We demonstrate that string loops can be
scattered near the black hole horizon, and the energy of string
oscillations can be efficiently converted to the energy of their linear
motion. Such a transmutation effect can potentially represent
acceleration of jets in active galactic nuclei and microquasars. We give
the conditions limiting energy available for conversion onto the jetlike
motion. Surprisingly, we are able to show that string loops starting
from rest can be accelerated up to velocities v˜c even in the
field of Schwarzschild black holes, if their angular momentum parameter
is low enough. Such loops could serve as an explanation of highly
relativistic jets observed in some quasars and active galactic nuclei.
The cosmic repulsion becomes important behind the so-called static
radius where it accelerates the linear motion of the string loops up to
velocity v=c that is reached at the cosmic horizon of the
Schwarzschild-de Sitter spacetimes independently of the angular momentum
parameter of the strings.
Read More
