The future ability to test theories of gravity with black-hole shadows

Fuente: arXiv
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Main Authors: Uniyal, Akhil, Dihingia, Indu K., Mizuno, Yosuke, Rezzolla, Luciano
Format: Preprint
Published: 2025
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author Uniyal, Akhil
Dihingia, Indu K.
Mizuno, Yosuke
Rezzolla, Luciano
author_facet Uniyal, Akhil
Dihingia, Indu K.
Mizuno, Yosuke
Rezzolla, Luciano
contents The horizon-scale images of supermassive black holes (BHs) by the Event Horizon Telescope Collaboration (EHT) have provided new opportunities to test general relativity and other theories of gravity. In view of future projects, such as the next-generation Event Horizon Telescope (ngEHT) and the Black-Hole Explorer (BHEX), having the potential of enhancing our ability to probe extreme gravity, it is natural to ask: \textit{how much can two black-hole images differ?} To address this question and assess the ability of these projects to test theories of gravity with black-hole shadows, we use general-relativistic magnetohydrodynamic and radiative-transfer simulations to investigate the images of a wide class of accreting BHs deviating from the Kerr solution. By measuring the mismatch between images of different BHs we show that future missions will be able to distinguish a large class of BHs solutions from the Kerr solution when the mismatch in the images exceeds values between $2\%$ and $5\%$ depending on the image-comparison metric considered. These results indicate future horizon-scale imaging with percent-level image fidelity can place meaningful observational constraints on deviations from the Kerr metric and thereby test strong-field predictions of general relativity.
format Preprint
id arxiv_https___arxiv_org_abs_2511_03789
institution arXiv
publishDate 2025
record_format arxiv
spellingShingle The future ability to test theories of gravity with black-hole shadows
Uniyal, Akhil
Dihingia, Indu K.
Mizuno, Yosuke
Rezzolla, Luciano
General Relativity and Quantum Cosmology
High Energy Astrophysical Phenomena
The horizon-scale images of supermassive black holes (BHs) by the Event Horizon Telescope Collaboration (EHT) have provided new opportunities to test general relativity and other theories of gravity. In view of future projects, such as the next-generation Event Horizon Telescope (ngEHT) and the Black-Hole Explorer (BHEX), having the potential of enhancing our ability to probe extreme gravity, it is natural to ask: \textit{how much can two black-hole images differ?} To address this question and assess the ability of these projects to test theories of gravity with black-hole shadows, we use general-relativistic magnetohydrodynamic and radiative-transfer simulations to investigate the images of a wide class of accreting BHs deviating from the Kerr solution. By measuring the mismatch between images of different BHs we show that future missions will be able to distinguish a large class of BHs solutions from the Kerr solution when the mismatch in the images exceeds values between $2\%$ and $5\%$ depending on the image-comparison metric considered. These results indicate future horizon-scale imaging with percent-level image fidelity can place meaningful observational constraints on deviations from the Kerr metric and thereby test strong-field predictions of general relativity.
title The future ability to test theories of gravity with black-hole shadows
topic General Relativity and Quantum Cosmology
High Energy Astrophysical Phenomena
url https://arxiv.org/abs/2511.03789