Overview: A Black Hole’s Weather, Not Just Its Shadow
The first image of a black hole, captured by the Event Horizon Telescope (EHT) in 2019, made M87* a household name in astronomy. But new time‑domain observations—from 2017, 2018, and 2021—reveal that the environment around this giant object is far less static than the shadow on its edge. Scientists mapped the polarization of light near M87*, tracing shifts in the magnetic field that surrounds the black hole’s event horizon. While the black hole’s silhouette remains stable, its magnetic weather is anything but quiet.
What the Observations Show
Researchers found that the magnetic field around M87* changed direction over just a few years. In 2017, the polarization pattern appeared to spiral clockwise. By 2018, it flipped to a counterclockwise (anti‑clockwise) orientation and seemed to settle briefly. By 2021, the polarization pattern again spiraled in the anti‑clockwise sense. This flip represents the first confirmed reversal of magnetic-field direction in a black hole’s near‑horizon environment, a striking clue about the turbulent plasma that roils just outside the event horizon.
Why Polarization Matters
Polarization tracks how light interacts with magnetic fields. In the vicinity of a black hole, magnetized plasma organizes into a dynamic disk around the equator. Some material, instead of crossing the event horizon, follows magnetic field lines toward the poles and is expelled as jets. Observing polarization therefore offers a window into the magnetic structures that guide whether matter feeds the black hole or powers its spectacular jets.
The Big Implications for Jets and Galaxy Evolution
Jets from supermassive black holes shape their host galaxies by redistributing energy and regulating star formation across vast scales. As Paul Tiede of the Harvard‑Smithsonian Center for Astrophysics explains, the geometry of the observed shadow continues to agree with Einstein’s predictions, while the polarization tells a story of a magnetized, dynamic plasma environment. In other words, the engine itself is changing its mood while the engine’s image remains steady.
What This Tells Us About Black Hole Physics
These results support the view that the magnetized plasma swirling near the event horizon is not a calm halo but a turbulent, evolving system. The changing magnetic field hints at complex magnetohydrodynamic processes that govern how gas feeds the black hole and how magnetic energy channels into jets that reach far into intergalactic space. This time‑resolved view challenges current models and drives home the idea that black holes, even when their shadows look the same, can host wildly variable magnetic environments.
Looking Ahead: A Moving Portrait of M87*
Researchers are optimistic about building a more complete, time‑lapse portrait of M87*. The EHT team plans rapid‑fire observations in 2026, aiming to produce the first “movie” of M87*, a sequence that would capture how polarization and magnetic fields evolve on short cosmic timescales. As Remo Tilanus of the University of Arizona notes, this marks a pioneering step in time‑domain black hole astrophysics and brings us closer to understanding how these cosmic giants feed and drive jets across the universe.
