Joseph Farah

University of California Santa Barbara, September 20, 12:00 pm

Inferring black hole spin from images of the photon ring

Abstract: Measuring the spin of a black hole is crucial for understanding its formation, evolution, and the extreme physics in its vicinity, including the dynamics of accretion disks and relativistic jets. The shadow of a black hole and the photon rings that encircle it are closely tied to the spin of the black hole and serve as a useful proxy for its measurement. Recently, interferometers such as the Event Horizon Telescope (EHT) have imaged the shadows of the largest black holes on the sky, and upcoming missions like the Black Hole Explorer (BHEX) will probe their horizons and photon rings with unprecedented resolution. In this talk, I will explain how future high-resolution images from EHT+BHEX will be used to measure the photon ring and infer the spin of black hole targets.