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    Equatorial photon motion in the Kerr-Newman spacetimes with a non-zero cosmological constant

    Zdeněk Stuchlík · Listopad 01, 2000 · Fyzika · 0 comments
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    Publication date: Nov 2000

    Abstract:
    Discussion of the equatorial photon motion in Kerr-Newman black-hole and
    naked-singularity spacetimes with a non-zero cosmological constant is
    presented. Both repulsive and attractive cosmological constants are
    considered. An appropriate `effective potential‘ governing the photon
    radial motion is defined, circular photon orbits are determined, and
    their stability with respect to radial perturbations is established. The
    spacetimes are divided into separated classes according to the
    properties of the `effective potential‘. There is a special class of
    Kerr-Newman-de Sitter black-hole spacetimes with the restricted
    repulsive barrier. In such spacetimes, photons with high positive and
    all negative values of their impact parameter can travel freely between
    the outer black-hole horizon and the cosmological horizon due to an
    interplay between the rotation of the source and the cosmological
    repulsion. It is shown that this type of behaviour of the photon motion
    is connected to an unusual relation between the values of the impact
    parameters of the photons and their directional angles relative to the
    outward radial direction as measured in the locally non-rotating frames.
    Surprisingly, some photons counterrotating in these frames have a
    positive impact parameter. Such photons can be both escaping or captured
    in the black-hole spacetimes with the restricted repulsive barrier. For
    the black-hole spacetimes with a standard, divergent repulsive barrier
    of the equatorial photon motion, the counterrotating photons with
    positive impact parameters must all be captured from the region near the
    black-hole outer horizon as in the case of Kerr black holes, while they
    all escape from the region near the cosmological horizon. Further, the
    azimuthal motion is discussed and photon trajectories are given in
    typical situations. It is shown that for some photons with negative
    impact parameter turning points of their azimuthal motion can exist.

    Authors:
    Stuchlík, Z.; Hledík, S.;

    https://ui.adsabs.harvard.edu/abs/2000CQGra..17.4541S

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