We study circular motion of charged test particles in the field of magnetized slowly rotating neutron stars. The gravitational field is approximated by the Lense-Thirring geometry, the magnetic field is of the standard dipole character. Using a fullyrelativistic approach we determine influence of the electromagnetic interaction (both attractive and repulsive) on the circular motion. We focus on the behaviour of the orbital frequency of the motion. Components of the four-velocity of the orbiting charged test particles are obtained by numerical solution of equations of motion. The role of the combined effect of the neutron star magnetic field and its rotation in the character of the orbital frequency 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 interactionc
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Collisionless astrophysical plasmas at kinetic equilibrium can exhibit geometrical structures characterized by the absence of well-defined global spatial symmetries. Plasmas of this type can arise in the surrounding of compact objects and are likely to give rise to relativistic regimes, being subject to intense gravitational and electromagnetic fields. This paper deals with the investigation of the physical mechanisms related to the occurrence of a non-vanishing equilibrium fluid stress-energy tensor associated with each collisionless species of plasma charged particles belonging to these systems. This permits one to obtain information about the thermal properties of the plasma and to display the related contributions generated by phase-space anisotropies. The issue is addressed from a theoretical perspective in the framework of a covariant Vlasov statistical description, based on the adoption of a relativistic gyrokinetic theory for the single-particle dynamics.
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Relativistic current-carrying string loop moving axisymmetrically along the axis of a Schwarzschild black hole is investigated as model of relativistic jet formation. Acceleration of the string loop along its axis of symmetry shows regular and also irregular dependence on initial conditions. We will apply the theory of chaotic scattering on this problem.
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We study transition from regular to chaotic motion in the neighbourhood of stable equilibrium point of a relativistic current-carrying string-loop located around Schwarzschild black hole. We demonstrate successive transfer from the purely regular, periodic motion through quasi-periodic motion to purely chaotic motion of the string loop, with increasing of its energy. We also calculated quasi-periodic fundamental frequencies, which are important for survival of corresponding KAM tori. Using maximal Lyapunov exponent we show how the chaoticity of the string loop motion changes with increase of the string loop energy
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We present a detailed comparison of several integration schemes applied to the dynamic system consisting of a charged particle on the Kerr background endowed with the axisymmetric electromagnetic test field. In particular, we compare the performance of the symplectic integrator with several non-symplectic routines and discuss under which circumstances we should choose the symplectic one and when we should switch to some other scheme. We are basically concerned with two crucial, yet opposing aspects - accuracy of the integration and CPU time consumption. The latter is generally less critical in our application while the highest possible accuracy is strongly demanded.
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We introduce a pseudo-Newtonian gravitational potential describing the gravitational field of Schwarzschild black hole surrounded by a quintessential field. We also show, how the geodesic motion reflected in behaviour of general relativistic effective potential can be alternatively described by the pseudo-Newtonian one.
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We have previously applied several models of high-frequency
quasi-periodic oscillations (HF QPOs) to estimate the spin of the
central Kerr black hole in the three Galactic microquasars, GRS
1915+105, GRO J1655-40, and XTE J1550-564. Here we explore the
alternative possibility that the central compact body is a
super-spinning object (or a naked singularity) with the external
space-time described by Kerr geometry with a dimensionless spin
parameter a ≡ cJ/GM2> 1. We calculate the relevant
spin intervals for a subset of HF QPO models considered in the previous
study. Our analysis indicates that for all but one of the considered
models there exists at least one interval of a> 1 that is compatible
with constraints given by the ranges of the central compact object mass
independently estimated for the three sources. For most of the models,
the inferred values of a are several times higher than the extreme Kerr
black hole value a = 1. These values may be too high since the spin of
superspinars is often assumed to rapidly decrease due to accretion when
a ≫ 1. In this context, we conclude that only the epicyclic and the
Keplerian resonance model provides estimates that are compatible with
the expectation of just a small deviation from a = 1.
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We demonstrate possible optical signatures of the Kehagias-Sfetsos (KS) naked singularity spacetimes representing a spherically symmetric vacuum solution of the modified Hořava gravity. In such spacetimes, accretion structures significantly different from those present in standard black hole spacetimes occur due to the 'antigravity' effect, which causes an internal static sphere surrounded by Keplerian discs. We focus our attention on the optical effects related to the Keplerian accretion discs, constructing the optical appearance of the Keplerian discs, the spectral continuum due to their thermal radiation, and the spectral profiled lines generated in the innermost parts of such discs. The KS naked singularity signature is strongly encoded in the characteristics of predicted optical effects, especially in cases where the spectral continuum and spectral lines are profiled by the strong gravity of the spacetimes due to the vanishing region of the angular velocity gradient influencing the effectiveness of the viscosity mechanism. We can conclude that optical signatures of KS naked singularities can be well distinguished from the signatures of standard black holes.
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We study the acceleration of an electric current-carrying and axially symmetric string loop initially oscillating in the vicinity of a Schwarzschild black hole embedded in an external asymptotically uniform magnetic field. The plane of the string loop is orthogonal to the magnetic field lines and the acceleration of the string loop occurs due to the transmutation effect turning in the deep gravitational field the internal energy of the oscillating strings to the energy of their translational motion along the axis given by the symmetry of the black hole spacetime and the magnetic field. We restrict our attention to the motion of string loop with energy high enough, when it can overcome the gravitational attraction and escape to infinity. We demonstrate that for the current-carrying string loop the transmutation effect is enhanced by the contribution of the interaction between the electric current of the string loop and the external magnetic field and we give conditions that have to be fulfilled for an efficient acceleration. The Schwarzschild black hole combined with the strong external magnetic field can accelerate the current-carrying string loop up to the velocities close to the speed of light v∼c. Therefore, the string loop transmutation effect can potentially well serve as an explanation for acceleration of highly relativistic jets observed in microquasars and active galactic nuclei.
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We demonstrate possible optical signatures of the Kehagias-Sfetsos (KS)
naked singularity spacetimes representing a spherically symmetric vacuum
solution of the modified Hořava gravity. In such spacetimes,
accretion structures significantly different from those present in
standard black hole spacetimes occur due to the
‘antigravity’ effect, which causes an internal static sphere
surrounded by Keplerian discs. We focus our attention on the optical
effects related to the Keplerian accretion discs, constructing the
optical appearance of the Keplerian discs, the spectral continuum due to
their thermal radiation, and the spectral profiled lines generated in
the innermost parts of such discs. The KS naked singularity signature is
strongly encoded in the characteristics of predicted optical effects,
especially in cases where the spectral continuum and spectral lines are
profiled by the strong gravity of the spacetimes due to the vanishing
region of the angular velocity gradient influencing the effectiveness of
the viscosity mechanism. We can conclude that optical signatures of KS
naked singularities can be well distinguished from the signatures of
standard black holes.
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