The current ability to test theories of gravity with black hole shadows

By Yosuke Mizuno, Z. Younsi, C. Fromm, Oliver Porth, M. De Laurentis, H. Olivares, Heino Falcke, Michael Kramer, Luciano Rezzolla. Nature Astronomy, 2018

282 citations recorded by the source corpus.

Our Galactic Centre, Sagittarius A*, is believed to harbour a supermassive black hole, as suggested by observations tracking individual orbiting stars1,2. Upcoming submillimetre very-long baseline interferometry images of Sagittarius A* carried out by the Event Horizon Telescope collaboration (EHTC)3,4 are expected to provide critical evidence for the existence of this supermassive black hole5,6. We assess our present ability to use EHTC images to determine whether they correspond to a Kerr black hole as predicted by Einstein’s theory of general relativity or to a black hole in alternative theories of gravity. To this end, we perform general-relativistic magnetohydrodynamical simulations and use general-relativistic radiative-transfer calculations to generate synthetic shadow images of a magnetized accretion flow onto a Kerr black hole. In addition, we perform these simulations and calculations for a dilaton black hole, which we take as a representative solution of an alternative theory of gravity. Adopting the very-long baseline interferometry configuration from the 2017 EHTC campaign, we find that it could be extremely difficult to distinguish between black holes from different theories of gravity, thus highlighting that great caution is needed when interpreting black hole images as tests of general relativity. The authors predict the ability of the Event Horizon Telescope (in its 2017 campaign) to distinguish between different theories of gravity based on images of Sagittarius A*; they suggest that it will not be possible.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/0bf26250413bec718bfb94c7530a26c20ced32f7

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In Astronomy and Astrophysics

Citations in the corpus

Black Hole Parameter Estimation from Its Shadow (2018, background): “…shadow (Bambi & Freese 2009; Johannsen & Psaltis 2010; Falcke & Markoff 2013; Broderick et al. 2014; Younsi et al. 2016; Giddings & Psaltis 2018; Mizuno et al. 2018; Breton et al. 2019; Held et al. 2019; Konoplya & Zhidenko 2019; Kumar et al. 2019; Long et al. 2019; Vagnozzi & Visinelli 2019;…”
Constraints on black-hole charges with the 2017 EHT observations of M87* (2021, result): “[50] has shown that the image libraries produced in this way would be very similar and essentially indistinguishable, given the present quality of the observations.”
First M87 Event Horizon Telescope Results. V. Physical Origin of the Asymmetric Ring (2019, unknown): “…shadows of this class of compact objects are expected to be similar to Kerr and therefore cannot be ruled out immediately by current observations (Mizuno et al. 2018), the most extreme examples of black holes surrounded by massive scalar field configurations should produce additional lobes in…”