A coordinate-independent characterization of a black hole shadow

By A. Abdujabbarov, Luciano Rezzolla, B. Ahmedov. 2015

210 citations recorded by the source corpus.

A large international effort is under way to assess the presence of a shadow in the radio emission from the compact source at the centre of our Galaxy, Sagittarius A* (Sgr A*). If detected, this shadow would provide the first direct evidence of the existence of black holes and that Sgr A* is a supermassive black hole. In addition, the shape of the shadow could be used to learn about extreme gravity near the event horizon and to determine which theory of gravity better describes the observations. The mathematical description of the shadow has so far used a number of simplifying assumptions that are unlikely to be met by the real observational data. We here provide a general formalism to describe the shadow as an arbitrary polar curve expressed in terms of a Legendre expansion. Our formalism does not presume any knowledge of the properties of the shadow, e.g. the location of its centre, and offers a number of routes to characterize the distortions of the curve with respect to reference circles. These distortions can be implemented in a coordinate-independent manner by different teams analysing the same data. We show that the new formalism provides an accurate and robust description of noisy observational data, with smaller error variances when compared to previous approaches for the measurement of the distortion.

Subfields: Astronomy and Astrophysics, Statistical and Nonlinear Physics

View Paper: https://www.semanticscholar.org/paper/98f9e963b5e5d665e51c0958d171e516a650b132

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In Astronomy and Astrophysics

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Citations in the corpus

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.”
Gravitational Lensing in Presence of Plasma: Strong Lens Systems, Black Hole Lensing and Shadow (2017, background): “Numerous analytical investigations and numerical simulations of the shadow are presented in literature (for example, see [90, 101, 95, 85, 86, 103, 104, 105, 94, 98, 99, 91, 106, 102, 97, 87, 88, 89, 93, 92, 96, 100, 110, 107, 108, 109, 111]).”
Constraints on black-hole charges with the 2017 EHT observations of M87* (2021, methodology): “[83], we use here the simplest one which was originally introduced in Ref.”
Black Hole Parameter Estimation from Its Shadow (2018, methodology): “…class of shadows, demanding some symmetries in their shapes, and they may not precisely work for black holes in some modified theories of gravity (Abdujabbarov et al. 2015b), which leads to the introduction of new observables (Schee & Stuchlik 2009; Johannsen 2013b; Tsukamoto et al. 2014;…”
Testing black hole candidates with electromagnetic radiation (2015, methodology): “17 [a more sophisticated method was presented in Abdujabbarov et al. (2015)].”