New images of the M87* black hole from the Event Horizon Telescope (EHT) — a planet-scale array of eight ground-based radio telescopes (ALMA, APEX, the IRAM 30-m telescope, the James Clerk Maxwell Telescope, the Large Millimeter Telescope Alfonso Serrano, the Submillimeter Array, the Submillimeter Telescope, and the South Pole Telescope) — reveal a dynamic environment with changing polarization patterns near the black hole.
As shown in these EHT images, while M87*’s magnetic fields appeared to spiral in one direction in 2017, they settled in 2018 and reversed direction in 2021. Image credit: EHT Collaboration.
Messier 87 is a giant elliptical galaxy located some 53 million light-years away in the constellation of Virgo.
Also known as M87, the galaxy harbors M87*, a supermassive black hole with a mass of more than 6 billion solar masses.
In 2017, the EHT Collaboration observed a spiraling polarization pattern that is the signature of a large-scale twisted magnetic structure, confirming long-held ideas about how black holes interact with, and impact, their environments.
But in 2018, the polarization all but disappeared. In 2021, the meager remnant began to spiral in the opposite direction.
Astrophysicists are now wrestling with a solitary question: why?
“Black holes hold their mysteries tight, but we are now prying the answers from their grasp,” said Professor Avery Broderick, an astrophysicist at the University of Waterloo and Perimeter Institute.
“Our team at Waterloo was central to reconstructing the images from the EHT data, and determining what we can be confident is real and what could be merely an instrumental artifact.”
“We have been at the forefront of understanding how EHT images, and especially their evolution, can reveal the astrophysical dramas unfolding on gravity’s most extreme stage.”
Year after year, the EHT Collaboration goes back to M87* to capture moments that show how it is evolving, knowing that each time, they will gain more insight into its long-guarded secrets.
“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 Dr. Paul Tiede, an astronomer at the Harvard & Smithsonian’s Center for Astrophysics.
“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.”
The stability of M87*’s shadow can be taken as evidence that ‘black holes have no hair,’ a decades-old metaphor meaning that black holes are simple geometric objects with no descriptive parameters beyond their mass, spin and charge.
“It’s one of the reasons why they’re so interesting as gravitational objects. You can make very crisp, clear predictions, and all the astrophysical phenomena don’t seem to matter a lot,” Professor Broderick said.
“But the stuff around it can have hair, and these magnetic fields are a striking example.”
“We’ve had a clear sense for what kind of magnetic hairstyles should be allowed for a long time, but now we’re seeing that, like with humans, you can get a lot of different hairstyles over four years.”
“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 Professor Mariafelicia De Laurentis, an astrophysicist at the University of Naples Federico II.
“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.”
The findings will be published in the journal Astronomy & Astrophysics.
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Kazunori Akiyama et al. (Event Horizon Telescope Collaboration). 2025. Horizon-scale variability of M87* from 2017-2021 EHT observations. A&A, in press; doi: 10.1051/0004-6361/202555855
