BHI Colloquium


Tuesday, September 22, 2020, 1:30pm to 2:30pm


Zoom link in description

Alex Lupsasca (Physics) - Princeton University


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

Abstract: 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.

Bio: Alex Lupsasca received his PhD in 2017 from the Harvard University Physics Department and was subsequently a postdoctoral fellow at the BHI.  He is currently an Associate Research Scholar at the Princeton Gravity Initiative.

Link to Zoom



See also: Physics