EHT tests of the strong-field regime of General Relativity. (arXiv:2011.06812v2 [gr-qc] UPDATED)
<a href="http://arxiv.org/find/gr-qc/1/au:+Volkel_S/0/1/0/all/0/1">Sebastian H. Völkel</a>, <a href="http://arxiv.org/find/gr-qc/1/au:+Barausse_E/0/1/0/all/0/1">Enrico Barausse</a>, <a href="http://arxiv.org/find/gr-qc/1/au:+Franchini_N/0/1/0/all/0/1">Nicola Franchini</a>, <a href="http://arxiv.org/find/gr-qc/1/au:+Broderick_A/0/1/0/all/0/1">Avery E. Broderick</a>
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.
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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