Located about 55 million light-years away from Earth, M87 harbors a supermassive black hole more than six billion times the mass of the Sun. The EHT, a global network of radio telescopes acting as an Earth-sized observatory, first captured the iconic image of M87’s black hole shadow in 2019. Now, by comparing observations from 2017, 2018, and 2021, scientists have taken the next step towards uncovering how the magnetic fields near the black hole change over time.

“What’s remarkable is that while the ring size has remained consistent over the years—confirming the black hole’s shadow predicted by Einstein’s theory—the polarization pattern changes significantly,” said Paul Tiede, an astronomer at the Center for Astrophysics | Harvard & Smithsonian, and a co-lead of the new study. “This tells us that the magnetized plasma swirling near the event horizon is far from static; it’s dynamic and complex, pushing our theoretical models to the limit.”

“Year after year, we improve the EHT – with additional telescopes and upgraded instrumentation, new ideas for scientific explorations, and novel algorithms to get more out of the data,” added co-lead Michael Janssen, an assistant professor at the Radboud University Nijmegen and member of the EHT science board. “For this study, all these factors nicely conspired into new scientific results and new questions, which will certainly keep us busy for many more years.”

New images from the Event Horizon Telescope (EHT) collaboration have revealed a dynamic environment with changing polarization patterns in the magnetic fields of the supermassive black hole M87*. As shown in the images above, while M87*’s magnetic fields appeared to spiral in one direction in 2017, they settled in 2018 and reversed direction in 2021. The cumulative effects of this polarization change over time suggests that M87* and its surrounding environment are constantly evolving.（Credit: EHT Collaboration）

Between 2017 and 2021, the polarization pattern flipped direction. In 2017, the magnetic fields appeared to spiral one way; by 2018, they settled; and in 2021, they reversed, spiraling the opposite direction. Some of these apparent changes in the polarization’s rotational direction may be influenced by a combination of internal magnetic structure and external effects, such as a Faraday screen. The cumulative effects of how this polarization changes over time suggests an evolving, turbulent environment where magnetic fields play a vital role in governing how matter falls into the black hole and how energy is launched outward.

“The fact that the polarization pattern flipped direction from 2017 to 2021 was totally unexpected,” Jongho Park, an astronomer at Kyunghee University and a collaborator on the project. “It challenges our models and shows there’s much we still don’t understand near the event horizon.”

Crucially, the 2021 EHT observations included two new telescopes—Kitt Peak in Arizona and NOEMA in France—which enhanced the array’s sensitivity and image clarity. This allowed scientists to constrain, for the first time with the EHT, the emission direction of the base of M87’s relativistic jet—a narrow beam of energetic particles blasting out from the black hole at nearly the speed of light. Upgrades at the Greenland Telescope and James Clerk Maxwell Telescope have further improved the data quality in 2021.

"The improved calibration has led to a remarkable boost in data quality and array performance, with new short baselines— between NOEMA and the IRAM 30m telescopes, and between Kitt Peak and SMT, providing the first constraints on the faint jet base emission,” said Sebastiano von Fellenberg, a postdoctoral fellow at the University of Toronto’s Canadian Institute for Theoretical Astrophysics (CITA), and postdoctoral researcher at the Max Planck Institute for Radio Astronomy (MPIfR) who focused on calibration for the project. “This leap in sensitivity also enhances our ability to detect subtle polarization signals.”

Jets like M87’s play a crucial role in galaxy evolution by regulating star formation and distributing energy on vast scales. Emitting across the electromagnetic spectrum—including gamma rays and neutrinos—M87’s powerful jet provides a unique laboratory to study how these cosmic phenomena form and are launched. This new detection offers a vital piece of the puzzle.

The research team at Tsung-Dao Lee Institute, Shanghai Jiao Tong University, led by Prof. Yosuke Mizuno, has contributed to developing a numerical library and the theoretical interpretation of this work.

“These multi-year images deepen our understanding of one of the Universe’s most extreme environments,” said Yosuke Mizuno, “They confirm Einstein’s predictions while revealing new, unexpected complexities about magnetic fields and jet formation near a supermassive black hole.”