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@article{33473,
author = {Charbulák, Daniel and Stuchlík, Zdeněk},
article_number = {11},
doi = {http://dx.doi.org/10.1140/epjc/s10052-018-6336-5},
keywords = {Kerr naked singularity; photon orbits; stable circular geodesics},
language = {eng},
issn = {1434-6044},
journal = {European Physical Journal C},
title = {Spherical photon orbits in the field of Kerr naked singularities},
url = {https://link.springer.com/article/10.1140%2Fepjc%2Fs10052-018-6336-5},
volume = {78},
year = {2018}
}
TY - JOUR
ID - 33473
AU - Charbulák, Daniel - Stuchlík, Zdeněk
PY - 2018
TI - Spherical photon orbits in the field of Kerr naked singularities
JF - European Physical Journal C
VL - 78
IS - 11
SP - "879-1"-"879-25"
EP - "879-1"-"879-25"
SN - 1434-6044
KW - Kerr naked singularity
KW - photon orbits
KW - stable circular geodesics
UR - https://link.springer.com/article/10.1140%2Fepjc%2Fs10052-018-6336-5
L2 - https://link.springer.com/article/10.1140%2Fepjc%2Fs10052-018-6336-5
N2 - For the Kerr naked singularity (KNS) spacetimes, we study properties of spherical photon orbits (SPOs) confined to constant Boyer-Lindquist radius r. Some new features of the SPOs are found, having no counterparts in the Kerr black hole (KBH) spacetimes, especially stable orbits that could be pure prograde/retrograde, or with turning point in the azimuthal direction. At r > 1 (r < 1) the covariant photon energy E > 0 (E < 0), at r = 1 there is E = 0. All unstable orbits must have E > 0. It is shown that the polar SPOs can exist only in the spacetimes with dimensionless spin a < 1.7996. Existence of closed SPOs with vanishing total change of the azimuth is demonstrated. Classification of the KNS and KBH spacetimes in dependence on their dimensionless spin a is proposed, considering the properties of the SPOs. For selected types of the KNS spacetimes, typical SPOs are constructed, including the closed paths. It is shown that the stable SPOs intersect the equatorial plane in a region of stable circular orbits of test particles, depending on the spin a. Relevance of this intersection for the Keplerian accretion discs is outlined and observational effects are estimated.
ER -
CHARBULÁK, Daniel and Zdeněk STUCHLÍK. Spherical photon orbits in the field of Kerr naked singularities. \textit{European Physical Journal C}. 2018, vol.~78, No~11, p.~''879-1''-''879-25'', 25 pp. ISSN~1434-6044. Available from: https://dx.doi.org/10.1140/epjc/s10052-018-6336-5.
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