Measurement of the Kerr Spin Parameter by Observation of a Compact Object's Shadow

By Kenta Hioki, K. Maeda. 2009

365 citations recorded by the source corpus.

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.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/40bbef88540cfeaaeae15a87b52df567381ca510

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Citations in the corpus

Constraints on black-hole charges with the 2017 EHT observations of M87* (2021, background): “where rsh;c is the radius of the circumcircle passing through the two points (since the images here are symmetric about the α-axis) with coordinates ðαr; 0Þ and ðαt; βtÞ, which are the rightmost and topmost points of the shadow curve, and is given as [80],”
Shadow of Kerr-Taub-NUT black hole (2012, neutral): “4 (Hioki and Maeda 2009).”
Shadows of spherically symmetric black holes and naked singularities (2018, background): “Many authors (Synge 1966; Zakharov 2014; Takahashi 2004; Hioki & Maeda 2009; Takahashi 2005; deVries 2000; Young 1976; Yumoto et al. 2012; Shipley & Dolan 2016) have studied the characteristics of shadows cast by various black holes.”
Silhouette of M87*: A new window to peek into the world of hidden dimensions (2019, background): “The shadow is formed when photons with small impact parameter originating from a source of electromagnetic radiation behind the BH gets trapped by its gravity [48–55] and hence fail to reach the observer.”
A coordinate-independent characterization of a black hole shadow (2015, methodology): “A way to measure this deformation was first suggested by Hioki & Maeda (2009) and then further developed by other authors (Bambi & Freese 2009; Bambi & Yoshida 2010; Bambi & Modesto 2013).”
Measuring the Kerr spin parameter of regular black holes from their shadow (2013, methodology): “[61], which is based on the determination of the distortion parameter δs = Dcs/Rs, where Dcs and Rs are, respectively, the dent and the radius of the shadow.”
Observing the shadow of Einstein-Maxwell-Dilaton-Axion black hole (2013, methodology): “However, another two new observables [26] can be adopted to describe the shadow of a naked singularity.”
Appearance of Keplerian discs orbiting Kerr superspinars (2010, methodology): “(For an analogous definition of parameters characterizing black-hole silhouettes see [25, 46, 71].”