Overview: A Dynamic Magnetic Field Around a Stable Shadow
Using observations from the Event Horizon Telescope (EHT) in 2017, 2018, and 2021, scientists have mapped how the polarization of light around M87* reveals changes in the magnetic field near the black hole’s edge. The results show that while the black hole’s shadow—the dark ring carved by gravity—remains remarkably stable, the magnetized plasma hugging the event horizon is anything but. In short, M87* exhibits wild, time‑dependent cosmic weather just outside its boundary.
Polarization is the key tracer here. When light travels through a magnetized environment, its waves tend to align in a particular direction. By overlaying polarization maps with the EHT’s high‑resolution images, researchers can infer how magnetic field lines thread the region around the black hole and how material flows toward and away from the horizon. The finding that the magnetic field changed direction from 2017 to 2021 marks the first time such a flip has been spotted in a black hole’s immediate surroundings.
From Clockwise to Anticlockwise: The Magnetic Flip Timeline
In 2017, the magnetic field around M87* appeared to spiral clockwise. By 2018, the pattern shifted to anticlockwise and seemed to settle into a new orientation. In 2021, the spiral again shifted, now rotating anticlockwise in a way that differed from 2017. The black hole itself remained virtually unchanged during this interval, preserving a consistent shadow and ring size that align with Einstein’s predictions. The distinct evolution of the polarization pattern shows that the magnetized plasma near the event horizon is dynamic, rearranging itself on relatively short cosmic timescales.
Why a Changing Magnetic Field Matters
Magnetic fields are thought to play a central role in launching and shaping the powerful jets that shoot material from the poles of accreting black holes into intergalactic space. As matter swirls into the black hole, the field lines guide some material along the poles, energizing jets that can extend for millions of light‑years. The new results imply that the environment fueling these jets is far from static. The polarization data indicate that the magnetized plasma near the horizon reorganizes itself as feeding and outflows fluctuate, driving a dynamic circuit of energy around the black hole.
Implications for Jet Physics and Accretion
What powers the dramatic jets and how they maintain their collimation across vast cosmic distances remain central questions in black hole astrophysics. The observed magnetic flips provide a fresh constraint for models of how matter behaves in extreme gravity, how magnetic fields extract energy, and how jets are launched from near the event horizon. As the field reorganizes, it can alter how efficiently material is funneled toward the poles, potentially changing jet speed, structure, and brightness over time.
The Emergence of Time‑Domain Black Hole Studies
“Pioneering a new frontier in time-domain black hole astrophysics, the Event Horizon Telescope is planning an ambitious series of rapid-fire observations across March and April 2026,” notes astronomer Remo Tilanus. The plan aims to capture near‑live movies of M87*, enabling scientists to map how the magnetic environment evolves in near real time. As Paul Tiede of the Harvard‑Smithsonian Center for Astrophysics puts it, the unchanging ring paired with shifting polarization patterns underscores how dynamic the magnetized plasma around a black hole truly is, pushing current theories to adapt to a time‑varying cosmos.
Looking Ahead
The 2017–2021 polarization changes in M87* open a new window into how supermassive black holes feed and regulate their surroundings. Future observations—especially rapid, repeated measurements—could turn the once‑static portrait of a black hole into a movie, revealing the choreography of accretion and jet formation in action. By building a catalog of such magnetic weather events in multiple black holes, astronomers hope to generalize the physics that governs some of the universe’s most extreme engines.
