Alexandru Lupsasca:  The Black Hole Photon Ring
Channel: lawphysics
Date: 2021-04-14

Webinar 111
Alexandru Lupsasca: The Black Hole Photon Ring
Princeton Gravity Initiative, USA. 

 Host: Alejandro Cárdenas-Avendaño, UIUC & Konrad Lorenz,

Abstract: The photon ring is a narrow ring-shaped feature, predicted by General Relativity 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. I will review the origin and structure of the photon ring, before discussing the prospects for its future detection. I will argue 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 strong-field General Relativity. A space-based interferometry experiment targeting the photon ring of M87* could test the Kerr nature of the source to the sub-sub-percent level.

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