Measuring the Kerr spin parameter of regular black holes from their shadow

By Zilong Li, Cosimo Bambi. 2013

152 citations recorded by the source corpus.

In a previous paper, one of us has showed that, at least in some cases, the Kerr-nature of astrophysical black hole candidates is extremely difficult to test and current techniques, even in presence of excellent data not available today, cannot distinguish a Kerr black hole from a Bardeen one, despite the substantial difference of the two backgrounds. In this paper, we investigate if the detection of the ``shadow'' of nearby super-massive black hole candidates by near future mm/sub-mm very long baseline interferometry experiments can do the job. More specifically, we consider the measurement of the Kerr spin parameter of the Bardeen and Hayward regular black holes from their shadow, and we then compare the result with the estimate inferred from the Kα iron line and from the frequency of the innermost stable circular orbit. For non-rotating black holes, the shadow approach provides different values, and therefore the Kerr black hole hypothesis can potentially be tested. For near extremal objects, all the approaches give quite similar results, and therefore it is not possible to constrain deviations from the Kerr solution. The present work confirms that it is definitively challenging to test this kind of metrics, even with future facilities. However, the detection of a source that looks like a fast-rotating Kerr black hole can put meaningful constraints on the nature of the compact object.

Subfields: Astronomy and Astrophysics, Atomic and Molecular Physics, and Optics

View Paper: https://www.semanticscholar.org/paper/e1e13be71bd099022b11df8b87eb791a8173de9a

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Citations in the corpus

Testing black hole candidates with electromagnetic radiation (2015, background): “…& Eiroa, 2012, 2013; Amarilla et al., 2010; Atamurotov et al., 2013a,b; Bambi, 2013f; Bambi et al., 2012; Bambi & Freese, 2009; Bambi & Yoshida, 2010; Ghasemi-Nodehi et al., 2015; Johannsen & Psaltis, 2010; Li & Bambi, 2014a; Schee & Stuchĺık, 2009; Tsukamoto et al., 2014; Wei & Liu, 2013).”
Constraining the spin and the deformation parameters from the black hole shadow (2014, methodology): “[48], two of us have studied the measurement of the Kerr spin parameter of Kerr BHs and non-Kerr regular BHs; that is, we measured the spin parameter a/M from the shape of the shadow of a BH assuming it was a Kerr BH.”
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]).”