Demonstrating Photon Ring Existence with Single-Baseline Polarimetry

Understand

Images of supermassive black hole accretion flows contain features of both curved spacetime and plasma structure.

• Inferring properties of the spacetime from images requires modeling the plasma properties, and vice versa.
• The Event Horizon Telescope Collaboration has imaged near-horizon millimeter emission from both Messier 87* (M87*) and Sagittarius A* (Sgr A*) with very-long-baseline interferometry (VLBI) and has found a preference for magnetically arrested disk (MAD) accretion in each case.
• MAD accretion enables spacetime measurements through future observations of the photon ring, the image feature composed of near-orbiting photons.