Measuring the black hole photon ring shape in the presence of instrumental noise and astrophysical fluctuations

General relativity predicts the existence of photon rings in black hole images, whose interferometric signature offers insight into the astrophysics-independent geometry of black holes. In this talk, I will discuss the impact of instrumental noise and astrophysical fluctuations on observations of the first photon ring's shape. I will first introduce an efficient fitting method capable of extracting the photon ring's shape. Then, I will analyze the effects of instrumental noise and astrophysical fluctuations on the accuracy of this fitting method. Our findings demonstrate that at and below some level of noise (around 1.5 milijansky), we can consistently obtain accurate fits for several astrophysical profiles. Additionally, we found that only a few time-indexed observational snapshots of the black hole are generally required to overcome the influence of astrophysical fluctuations.