Abstract
We study shadows of regular rotating black holes described by the axially symmetric solutions asymptotically Kerr for a distant observer, obtained from regular spherical solutions of the Kerr–Schild class specified by T t t = T r r ( p r = − ε ) . All regular solutions obtained with the Newman–Janis algorithm belong to this class. Their basic generic feature is the de Sitter vacuum interior. Information about the interior content of a regular rotating de Sitter-Kerr black hole can be in principle extracted from observation of its shadow. We present the general formulae for description of shadows for this class of regular black holes, and numerical analysis for two particular regular black hole solutions. We show that the shadow of a de Sitter-Kerr black hole is typically smaller than that for the Kerr black hole, and the difference depends essentially on the interior density and on the pace of its decreasing.
Highlights
The shadow of a black hole represents a dark spot appearing over an image of a bright source of radiation and seen by a distant observer as a direct dark image of a black hole, whose boundary is determined by the photon gravitational capture cross-section confined by the innermost unstable photon orbits ([1,2] and references therein)
All regular black hole solutions obtained by the Newman–Janis algorithm presented in the literature belong to the Kerr–Schild class and describe the de Sitter-Kerr black holes
We present the basic general formulae which describe shadows of regular rotating black holes obtained from regular spherical solutions with using the Newman–Janis algorithm
Summary
The shadow of a black hole represents a dark spot appearing over an image of a bright source of radiation and seen by a distant observer as a direct dark image of a black hole, whose boundary is determined by the photon gravitational capture cross-section confined by the innermost unstable photon orbits ([1,2] and references therein). All regular black hole solutions obtained by the Newman–Janis algorithm presented in the literature belong to the Kerr–Schild class and describe the de Sitter-Kerr black holes (for a review [35]). For the first type interior, a related spherical solution violates the dominant energy condition, and the interior of a rotating solution reduces to the de Sitter vacuum disk and satisfies the weak energy condition. Some information on the interior content of a regular rotating black hole can be in principle extracted from observation of its shadow, whose boundary is determined by the metric as the photons gravitational capture cross-section, which gives the apparent image of the black hole on the background of the image of the source of radiation.
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