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arXiv · 2011.06812

EHT tests of the strong-field regime of General Relativity

Sebastian H. Völkel·Enrico Barausse·Nicola Franchini·Avery E. Broderick
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Abstract

Following up on a recent analysis by Psaltis et al. [Phys. Rev. Lett. 125, 141104 (2020)], we show that the observed shadow size of M87$^*$ can be used to unambiguously and robustly constrain the black hole geometry in the vicinity of the circular photon orbit. Constraints on the post-Newtonian weak-field expansion of the black hole's metric are instead more subtle to obtain and interpret, as they rely on combining the shadow-size measurement with suitable theoretical priors. We provide examples showing that post-Newtonian constraints resulting from shadow-size measurements should be handled with extreme care. We also discuss the similarities and complementarity between the EHT shadow measurements and black-hole gravitational quasi-normal modes.

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Sebastian H. Völkel, Enrico Barausse, Nicola Franchini, Avery E. Broderick. 2020-11-13. EHT tests of the strong-field regime of General Relativity. https://doi.org/10.1088/1361-6382%2Fac27ed

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