On magnetic-field-induced non-geodesic corrections to relativistic orbital and epicyclic frequencies

    by Zdeněk Stuchlík· 01 února, 2010· in Fyzika· 0 comments
    We discuss non-geodesic corrections to orbital and epicyclic frequencies of charged test particles orbiting a non-rotating neutron star with a dipole magnetic field. Using a fully relativistic approach we consider the influence of both the magnetic attraction and repulsion on the orbital and epicyclic motion. The magnetic repulsion introduces a rather complex and unusual behaviour of the circular orbital motion that is well defined down to the radius where the vertical epicyclic frequency loses its meaning. We demonstrate that for the intensity of the magnetic interaction appropriately restricted, the stable circular orbits extend down to the magnetic innermost stable circular orbit (MISCO) that is located well under the geodetic innermost stable circular orbit (GISCO) and even can reach the region under the photon circular orbit. The lowest stable circular orbit at rMISCOmin = 2.73M, associated with the highest possible orbital frequency nu _{K}^{max} = 3284, Hz (1.5 , {it M}_{odot}/it M) , corresponds to the critical value of the particle-specific charge and the neutron star magnetic dipole moment product (tilde{q} mu )_crit = 1.87 M^2 . For the magnetic attraction acting above the GISCO, the situation is much more simple and we demonstrate that the most significant correction arises for the radial epicyclic frequency and consequently for the location of the MISCO when the strong magnetic attraction pushes its location far behind the location of GISCO. We show that the Lorentz force also naturally violates the equality of the orbital and vertical epicyclic frequencies implied by the spherical symmetry of the background Schwarzschild geometry giving rise to the new effect of nodal precession of the orbital motion plane. Finally, we apply the magnetic attraction corrections on the relativistic precession model of the twin-peak high-frequency quasiperiodic oscillations observed in the galactic low mass x-ray binaries, showing possible high relevance of the modified radial epicyclic frequency.
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    On magnetic-field-induced non-geodesic corrections to relativistic orbital and epicyclic frequencies

    by Zdeněk Stuchlík· 01 února, 2010· in Fyzika· 0 comments
    We discuss non-geodesic corrections to orbital and epicyclic frequencies of charged test particles orbiting a non-rotating neutron star with a dipole magnetic field. Using a fully relativistic approach we consider the influence of both the magnetic attraction and repulsion on the orbital and epicyclic motion. The magnetic repulsion introduces a rather complex and unusual behaviour of the circular orbital motion that is well defined down to the radius where the vertical epicyclic frequency loses its meaning. We demonstrate that for the intensity of the magnetic interaction appropriately restricted, the stable circular orbits extend down to the magnetic innermost stable circular orbit (MISCO) that is located well under the geodetic innermost stable circular orbit (GISCO) and even can reach the region under the photon circular orbit. The lowest stable circular orbit at rMISCOmin = 2.73M, associated with the highest possible orbital frequency nu _{K}^{max} = 3284, Hz (1.5 , {it M}_{odot}/it M) , corresponds to the critical value of the particle-specific charge and the neutron star magnetic dipole moment product (tilde{q} mu )_crit = 1.87 M^2 . For the magnetic attraction acting above the GISCO, the situation is much more simple and we demonstrate that the most significant correction arises for the radial epicyclic frequency and consequently for the location of the MISCO when the strong magnetic attraction pushes its location far behind the location of GISCO. We show that the Lorentz force also naturally violates the equality of the orbital and vertical epicyclic frequencies implied by the spherical symmetry of the background Schwarzschild geometry giving rise to the new effect of nodal precession of the orbital motion plane. Finally, we apply the magnetic attraction corrections on the relativistic precession model of the twin-peak high-frequency quasiperiodic oscillations observed in the galactic low mass x-ray binaries, showing possible high relevance of the modified radial epicyclic frequency.
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    Neutron star mass and spin implied by models of twin-peak quasiperiodic oscillations

    by Zdeněk Stuchlík· 01 ledna, 2010· in Fyzika· 0 comments
    Binary pulsars represent a good laboratory for testing field theories in strong field regime. In such cases, the effects of non-linear terms in these theories would be easily measured. In the present work, we discuss an exact solution of Einstein's field equations, in a field representing a binary compact object. The solution is a time-dependent one, which reduces to Curzon field, in the static case. The equations of motion of a test particle in the above mentioned field are formulated and solved. These equations can be used to study the motion of a third body (or a photon) in the field of a binary system.
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    Superspinars as an alternative to black holes

    by Zdeněk Stuchlík· 01 ledna, 2010· in Fyzika· 0 comments
    We present results of the study of some astrophysical phenomena taking place in the vicinity of superspinars, described by the Kerr naked singularity spacetime, that are capable to explain optical and other effects usually attributed to rotating black holes.
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    Relativistic Dynamics with Cosmological Constant:. Circular Geodesic Motion of Test Particles

    by Zdeněk Stuchlík· 27 listopadu, 2009· in Fyzika· 0 comments
    We present results of our recent studies concerning effects of Λ > 0 in astrophysically motivated problems. Here we summarize properties of circular geodesic motion of test particles in the equatorial plane of Kerr-de Sitter black-hole and naked-singularity spacetimes. Along with the standard analysis of geodesic equations of the ordinary geometry, we introduce alternative inertial forces formalism defined within the General Theory of Relativity in the framework of optical reference geometry.
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    Relativistic Dynamics with Cosmological Constant:. Spinning Test Particles and Perfect Fluid Tori

    by Zdeněk Stuchlík· 27 listopadu, 2009· in Fyzika· 0 comments
    Results of our recent studies concerning possible effects of Λ > 0 for equilibrium positions of spinning test particles and stationary configurations of perfect-fluid tori are presented.
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    Optical Phenomena in the Field of Braneworld Kerr Black Holes

    by Zdeněk Stuchlík· 27 listopadu, 2009· in Fyzika· 0 comments
    We study the influence of the tidal charge parameter of the braneworld models on some optical phenomena in rotating black hole space-times. The escape photon cones are determined for special families of locally nonrotating, circular geodetical and radially free-falling observers. The silhouette of a rotating black hole, the shape of an equatorial thin accretion disk and the time delay effect for direct and indirect images of a radiating hot spot orbiting the black hole are given and classified in terms of the black hole rotational and tidal parameters. It is shown that increase of the negatively valued tidal parameter, with the rotational parameter fixed, generally strengthens the relativistic effects and suppresses the rotation-induced asymmetries in the optical phenomena.
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    Pseudo-Newtonian and general relativistic barotropic tori in Schwarzschild-de Sitter spacetimes

    by Zdeněk Stuchlík· 01 listopadu, 2009· in Fyzika· 0 comments
    Pseudo-Newtonian gravitational potential introduced in spherically symmetric black-hole spacetimes with a repulsive cosmological constant is tested for equilibrium toroidal configurations of barotropic perfect fluid orbiting the black holes. Shapes and potential depths are determined for the marginally stable barotropic tori with uniform distribution of specific angular momentum, using both the pseudo-Newtonian and fully relativistic approach. For the adiabatic (isoentropic) perfect fluid, temperature profiles, mass-density and pressure profiles and total masses of pseudo-Newtonian and relativistic tori are compared providing important information on the relevance of the test-disc approximation in both the approaches. It is shown that the pseudo-Newtonian approach can be precise enough and useful for the modelling of accretion discs in the Schwarzschild-de Sitter spacetimes with the cosmological parameter y = ΛM2/3 lsim 10-6. For astrophysically relevant black holes with y < 10-25, this statement is tested and shown to be precise in few per cent for both accretion and excretion tori and for the marginally bound, i.e. maximally extended, tori allowing simultaneous inflow to the black hole and outflow to the outer space.
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    Pseudo-Newtonian and general relativistic barotropic tori in Schwarzschild-de Sitter spacetimes

    by Zdeněk Stuchlík· 01 listopadu, 2009· in Fyzika· 0 comments
    Pseudo-Newtonian gravitational potential introduced in spherically symmetric black-hole spacetimes with a repulsive cosmological constant is tested for equilibrium toroidal configurations of barotropic perfect fluid orbiting the black holes. Shapes and potential depths are determined for the marginally stable barotropic tori with uniform distribution of specific angular momentum, using both the pseudo-Newtonian and fully relativistic approach. For the adiabatic (isoentropic) perfect fluid, temperature profiles, mass-density and pressure profiles and total masses of pseudo-Newtonian and relativistic tori are compared providing important information on the relevance of the test-disc approximation in both the approaches. It is shown that the pseudo-Newtonian approach can be precise enough and useful for the modelling of accretion discs in the Schwarzschild-de Sitter spacetimes with the cosmological parameter y = ΛM2/3 lsim 10-6. For astrophysically relevant black holes with y < 10-25, this statement is tested and shown to be precise in few per cent for both accretion and excretion tori and for the marginally bound, i.e. maximally extended, tori allowing simultaneous inflow to the black hole and outflow to the outer space.
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    Profiles of emission lines generated by rings orbiting braneworld Kerr black holes

    by Zdeněk Stuchlík· 01 srpna, 2009· in Fyzika· 0 comments
    In the framework of the braneworld models, rotating black holes can be described by the Kerr metric with a tidal charge representing the influence of the non-local gravitational (tidal) effects of the bulk space Weyl tensor onto the black hole spacetime. We study the influence of the tidal charge onto profiled spectral lines generated by radiating tori orbiting in vicinity of a rotating black hole. We show that with lowering the negative tidal charge of the black hole, the profiled line becomes to be flatter and wider keeping their standard character with flux stronger at the blue edge of the profiled line. The extension of the line grows with radius falling and inclination angle growing. With growing inclination angle a small hump appears in the profiled lines due to the strong lensing effect of photons coming from regions behind the black hole. For positive tidal charge ( b > 0) and high inclination angles two small humps appear in the profiled lines close to the red and blue edge of the lines due to the strong lensing effect. We can conclude that for all values of b, the strongest effect on the profiled lines shape (extension) is caused by the changes of the inclination angle.
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