Abstract <p>In our paper published in 2005, it was predicted that the shadow near the Galactic Center (GC) black hole could be reconstructed from results of observations of the global VLBI system operating in the millimeter or submillimeter range. This prediction became reality in 2022, when shadows near black holes in the GC and the center of the galaxy M87 (in 2019) were reconstructed from data of observations of the Event Horizon Telescope collaboration, and these results led to the appearance of a large number of theoretical papers that considered constraints on both alternative models of galactic centers and alternative theories of gravity. For Schwarzschild, Kerr, and Reissner–Nordström black holes, the impact parameters corresponding to circular photon orbits determine the shadow shape and size; however, as was shown in the abovementioned paper, in the cases of some metrics, the existence of circular photon orbits is possible, though shadows for these metrics are not formed. A number of recent papers (including one published in the journal <i>PEPAN Letters</i>) have put forth, without evidence, alternative models of galactic centers in which parameters corresponding to circular photon orbits determine the shadow shape and size.</p>

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Shadows and Circular Photon Orbits: Consideration of Some Cases of Generalizations of Kerr–Newman Black Holes

  • A. F. Zakharov

摘要

Abstract

In our paper published in 2005, it was predicted that the shadow near the Galactic Center (GC) black hole could be reconstructed from results of observations of the global VLBI system operating in the millimeter or submillimeter range. This prediction became reality in 2022, when shadows near black holes in the GC and the center of the galaxy M87 (in 2019) were reconstructed from data of observations of the Event Horizon Telescope collaboration, and these results led to the appearance of a large number of theoretical papers that considered constraints on both alternative models of galactic centers and alternative theories of gravity. For Schwarzschild, Kerr, and Reissner–Nordström black holes, the impact parameters corresponding to circular photon orbits determine the shadow shape and size; however, as was shown in the abovementioned paper, in the cases of some metrics, the existence of circular photon orbits is possible, though shadows for these metrics are not formed. A number of recent papers (including one published in the journal PEPAN Letters) have put forth, without evidence, alternative models of galactic centers in which parameters corresponding to circular photon orbits determine the shadow shape and size.