New EHT Images Reveal Unexpected Polarization Flips at M87*
Multi-year Event Horizon Telescope observations capture evolving polarization patterns in supermassive black hole and see emissions in 230 GHz near the base of its jet
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Released: 16th Sep, 2025, Academia Sinica Institute of Astronomy & Astrophysics (ASIAA), Taiwan
The Event Horizon Telescope (EHT) collaboration has unveiled new, detailed images of the supermassive black hole at the center of the galaxy M87— known as M87*— revealing a dynamic environment with changing polarization patterns near the black hole. Additionally, the scientists found the first signatures of the extended jet emission near the jet base, which connects to the ring around M87*, in EHT data. These new observations, published today Astronomy & Astrophysics, are providing new insight into how matter and energy behave in the extreme environments surrounding black holes.
The Event Horizon Telescope (EHT) collaboration has unveiled new, detailed images of the supermassive black hole at the center of the galaxy M87— known as M87*— revealing a dynamic environment with changing polarization patterns near the black hole. Additionally, the scientists found the first signatures of the extended jet emission near the jet base, which connects to the ring around M87*, in EHT data. These new observations, published today Astronomy & Astrophysics, are providing new insight into how matter and energy behave in the extreme environments surrounding black holes.
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 published 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.”
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, a visiting scholar at Academia Sinica Institute of Astronomy and Astrophysics (ASIAA) and a collaborator on the project. “It challenges our models and shows there’s much we still don’t understand near the event horizon.”
"The 2021 EHT observations were conducted despite the global COVID19 pandemic. Many telescopes of the EHT array struggled to organize support for the campaign, particularly difficult for the Greenland Telescope (GLT) as it's at a distant remote site," commented Chih-Wei Locutus Huang, GLT/VLBI Support Scientist at ASIAA. "We utilized the still-in-development remote operation capability of the telescope, and successfully fulfilled the mission. The established remote operation procedures later significantly improve the management and scheduling of telescope operations."
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 Humboldt Feodor Lynen Fellow at the 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.
“These results show how the EHT is evolving into a fully fledged scientific observatory, capable not only of delivering unprecedented images, but of building a progressive and coherent understanding of black hole physics,” said Mariafelicia De Laurentis, a professor of astronomy at the University of Naples and EHT project scientist. “Each new campaign expands our horizon, from the dynamics of plasma and magnetic fields to the role of black holes in cosmic evolution. It is a concrete demonstration of the extraordinary scientific potential of this instrument.”
As the Event Horizon Telescope collaboration continues to expand its observational capabilities, these new results illuminate the dynamic environment surrounding M87* and deepen scientists’ understanding of black hole physics.
New images from the Event Horizon Telescope (EHT) collaboration have revealed a dynamic environment with changing polarization patterns in the magnetic fields of supermassive black hole M87*. As shown in the images above, while M87*’s magnetic fields appeared to spiral 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
More Information:
The EHT collaboration involves more than 400 researchers from Africa, Asia, Europe, and North and South America. The international collaboration is working to capture the most detailed black hole images ever obtained by creating a virtual Earth-sized telescope. Supported by considerable international investment, the EHT links existing telescopes using novel systems, creating a fundamentally new instrument with the highest angular resolving power that has yet to be achieved.
The individual telescopes involved are ALMA, APEX, the IRAM 30-meter Telescope, the IRAM NOEMA Observatory, the James Clerk Maxwell Telescope (JCMT), the Large Millimeter Telescope (LMT), the Submillimeter Array (SMA), the Submillimeter Telescope (SMT), the South Pole Telescope (SPT), the Kitt Peak Telescope, and the Greenland Telescope (GLT). Data were correlated at the Max-Planck-Institut für Radioastronomie (MPIfR) and MIT Haystack Observatory. The postprocessing was done within the collaboration by an international team at different institutions.
The EHT consortium consists of 13 stakeholder institutes: the Academia Sinica Institute of Astronomy and Astrophysics, the University of Arizona, the University of Chicago, the East Asian Observatory, Goethe University Frankfurt, Institut de Radioastronomie Millimétrique, Large Millimeter Telescope, Max Planck Institute for Radio Astronomy, MIT Haystack Observatory, National Astronomical Observatory of Japan, Perimeter Institute for Theoretical Physics, Radboud University, and the Smithsonian Astrophysical Observatory.
This research was presented in a paper "Horizon-scale variability of from 2017--2021 EHT observations" by The Event Horizon Telescope Collaboration, Astronomy & Astrophysics, September 16, 2025
Media Contact:
Media Contact:
Dr. Chih-Wei Locutus Huang, +886-2-2366-5425, cwhuang@asiaa.sinica.edu.tw
Dr. Mei-Yin Chou, +886-2-2366-5415, cmy@asiaa.sinica.edu.tw
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