Overview

• A peer‑reviewed Astronomy & Astrophysics paper reports that M87*’s polarization reversed between 2017 and 2021 across Event Horizon Telescope campaigns.
• Despite the changes, the black hole’s bright ring stayed the same size, reinforcing general relativity’s shadow prediction.
• The expanded 2021 array, including Kitt Peak and NOEMA with additional upgrades, boosted sensitivity and revealed emission constraints at the jet base.
• The polarization evolution and improved calibration expose hours‑scale variability in magnetized plasma near the event horizon that strains current models.
• The collaboration is preparing more frequent and continuous observations to build time‑resolved views and probe the cause of the changes.