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The Shape of the Black Hole Photon Ring: A Precise Test of Strong-Field General Relativity

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arxiv 2008.03879 v2 pith:ZFNQR32Z submitted 2020-08-10 gr-qc astro-ph.HEhep-th

Samuel E. Gralla , Alexandru Lupsasca , Daniel P. Marrone This is my paper · ORCID
classification gr-qcastro-ph.HEhep-th
keywords photonringtestblackholegeneralkerrprecise
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We propose a new test of strong-field general relativity (GR) based on the universal interferometric signature of the black hole photon ring. The photon ring is a narrow ring-shaped feature, predicted by GR but not yet observed, that appears on images of sources near a black hole. It is caused by extreme bending of light within a few Schwarzschild radii of the event horizon and provides a direct probe of the unstable bound photon orbits of the Kerr geometry. We show that the precise shape of the observable photon ring is remarkably insensitive to the astronomical source profile and can therefore be used as a stringent test of GR. We forecast that a tailored space-based interferometry experiment targeting M87* could test the Kerr nature of the source to the sub-sub-percent level.

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Cited by 17 Pith papers

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