M87*: A Supermassive Black Hole With Dynamic Magnetic Weather
When scientists released the first image of a black hole in 2019, the focus was on the shadow and the surrounding glow. But new time-series data from the Event Horizon Telescope (EHT) reveal something equally dramatic and unexpected: the magnetic field near M87*’s edge is not static. Across measurements taken in 2017, 2018, and 2021, the polarization patterns mapped onto the surrounding magnetized plasma show a tropical-type of weather, with magnetic directions flipping and reconfiguring over relatively short cosmic timescales.
A Timeline of Polarization Shifts
Researchers tracked how light’s polarization—its orientation as it travels through the magnetized environment near the black hole—changed over time. In 2017, the polarization pattern suggested a clockwise spiral of magnetic fields around the ring. By 2018, the pattern flipped to anticlockwise and appeared to stabilize, and by 2021 the pattern again emphasized an anticlockwise rotation. The striking result is that while the black hole itself—the mass, the ring, and the shadow—stayed remarkably consistent, its surrounding magnetic scaffolding was anything but calm.
Why Polarization Matters Near a Black Hole
Light becomes polarized when it travels through strongly magnetized plasma. By studying these polarization maps, scientists infer the geometry and strength of magnetic fields that thread the plasma just outside the event horizon. Since magnetic fields are believed to drive how matter swirls toward the hole and how jets are launched from the poles, changes in polarization offer a crucial window into the engine of one of the universe’s most powerful accelerators.
What This Says About Jets and Accretion
Jets are colossal streams of charged particles that shoot out from the regions near a black hole at nearly light speed. The magnetic field is thought to shepherd and accelerate material from the accretion disk into these jets. The observed polarization flips indicate that the magnetized plasma near M87* is in motion on timescales that astronomers can begin to map. This dynamism helps explain why jets can remain highly collimated and intermittently variable, even as the black hole’s mass and shadow remain constant.
Einstein’s Shadow Remains a Steady Reference
Across the years, the ring around M87* keeps its size within the predictions of general relativity, reinforcing confidence in Einstein’s theory in the strong-gravity regime. Yet, the surrounding environment proves to be anything but dull. As one astronomer notes, the stable shadow acts like a stage, while the surrounding magnetized plasma performs a complex, evolving routine around it.
Implications for Galaxy Evolution and Black Hole Feeding
Jets influence how galaxies grow by redistributing energy and matter on colossal scales. By unraveling how magnetic fields organize and reorganize themselves near the event horizon, scientists gain clues about how black holes regulate star formation in their hosts. The dynamic magnetized environment around M87* demonstrates that these giants not only sculpt their surroundings through gravity but also through turbulent, time-variable magnetic activity.
Looking Ahead: A Movie of M87*
Time-domain black hole astrophysics is entering an era of rapid-fire observations. Scientists plan more frequent measurements with the EHT, aiming to capture a “movie” of M87* that traces how its polarization and magnetic field evolve in near real time. Such campaigns could illuminate how the inner accretion flow feeds the black hole and powers jet-launching processes, providing a richer narrative of cosmic weather around these cosmic behemoths.
As Remo Tilanus of the University of Arizona’s Steward Observatory puts it, the goal is to turn snapshots into a moving picture that reveals the physical processes at work near the event horizon. The coming years may finally deliver the first-time-lapse view of M87* in action, linking magnetic dynamics to the grand-scale activity we observe in distant galaxies.
