Measurement of the Kerr spin parameter by observation of a compact object's shadow

Kenta Hioki, Keiichi Maeda

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139 Citations (Scopus)


A black hole casts a shadow as an optical appearance because of its strong gravitational field. We study how to determine the spin parameter and the inclination angle by observing the apparent shape of the shadow, which is distorted mainly by those two parameters. Defining some observables characterizing the apparent shape (its radius and distortion parameter), we find that the spin parameter and inclination angle of a Kerr black hole can be determined by the observation. This technique is also extended to the case of a Kerr naked singularity.

Original languageEnglish
Article number024042
JournalPhysical Review D - Particles, Fields, Gravitation and Cosmology
Issue number2
Publication statusPublished - 2009 Aug 6
Externally publishedYes


ASJC Scopus subject areas

  • Nuclear and High Energy Physics

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