Variable Magnetic Fields Around Black Hole M87*

Event Horizon Telescope observations capture evolving polarization patterns around the supermassive black hole at the center of the galaxy M87

To the point

• New event-horizon-telescope (EHT) images of M87* reveal unexpected flips in polarized light between 2017 and 2021, showing that magnetic fields near the black hole are dynamic and evolving.

• For the first time, the EHT detects faint jet emission near the base of M87's relativistic jet, enabled by added telescopes and improved calibration.

• These findings confirm Einstein's predictions of a stable black hole shadow while uncovering surprising turbulence in magnetic fields and jet formation.

The Event Horizon Telescope (EHT) collaboration, with a substantial contribution from the Max Planck Institute for Radio Astronomy (MPIfR), has unveiled new, detailed images of the supermassive black hole at the center of the galaxy M87. These reveal a dynamic environment with changing polarization patterns near the black hole. For the first time in EHT data, scientists have also detected signatures of jet emission near the base of the jet that emerges from the close environment of the black hole. These new observations, published in Astronomy & Astrophysics, offer fresh insight into how matter and energy behave in the extreme environments surrounding black holes.

Located about 55 million light-years 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, adding polarization maps in 2021. In astronomy, polarization refers to the alignment of light waves, which provides information about the structure and strength of magnetic fields in space. In the case of active galaxies, such as M87, magnetic fields play a crucial role. According to current theories, they are anchored in the plasma of matter orbiting the black hole in a disk, where they coil into magnetic towers that unleash enormous forces. The enclosed magnetic energy is capable of accelerating matter along jets that are stabilized by the twisted magnetic fields to nearly the speed of light. And these jets, which originate from an extremely compact region around the black hole, affect the entire galaxy, which is millions to billions of times larger: "Jets like the one in M87 play a key role in shaping the evolution of their host galaxies. By regulating star formation and distributing energy across vast distances, they affect the life cycle of matter on cosmic scales", explains Eduardo Ros from MPIfR.

However, more detailed observations are needed to clarify exactly how such jets form in the dynamic environment of black holes. The data now published make an important contribution here. As opposed to a single snapshot, they provide a series of images that capture for the first time how the dynamic magnetized environment of M87* changed in 2017, 2018, and 2021. This data is based on the continuous development of the Event Horizon Telescope: "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," adds Michael Janssen from Radboud University Nijmegen.

Changing Polarization Pattern of M87*

Between 2017 and 2021, the polarization pattern unexpectedly flipped direction. In 2017, the magnetic fields appeared to spiral one way; by 2018, they had stabilized, and in 2021, they reversed, spiraling the opposite way. Such changes may result from both the black hole's own magnetic structure and intervening matter that twists the light's polarization on its journey to Earth. Together, these variations point to an evolving, turbulent environment in which magnetic fields play a crucial role in directing how matter falls into the black hole and how energy is directed into the jet moving outward. This surprising behavior challenges existing models and underscores how much remains to be understood about processes near the event horizon.

"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," says Paul Tiede, an astronomer at the Center for Astrophysics, Harvard & Smithsonian. "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."

Two New Telescopes in the EHT Network

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-environment at nearly the speed of light. Technical performance 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," says Sebastiano von Fellenberg from the University of Toronto, former scientist at MPIfR, who focused on the calibration for the project. "This leap in sensitivity also enhances our ability to detect subtle polarization signals."

These multi-year observations reveal just how turbulent and dynamic the environment is close to the event horizon. They confirm Einstein's predictions while uncovering new complexities in magnetic fields and jet formation, offering an unprecedented view of the black hole's immediate surroundings. The next step will be to capture the variations of ring and jet with more frequent observations, ideally in a movie.

MPG/BEU based on the original press release of the MPIfR

Background Information

The EHT collaboration involves more than 400 researchers from Africa, Asia, Europe, North and South America, with around 270 participating in this paper. The international collaboration aims to capture the most detailed images of black holes using a virtual Earth-sized telescope. Supported by considerable international efforts, the EHT links existing telescopes using novel techniques to create a fundamentally new instrument with the highest angular resolving power that has yet been achieved.

The EHT consortium consists of 13 stakeholder institutes; the Academia Sinica Institute of‬ Astronomy and Astrophysics, the University of Arizona, the Center for Astrophysics | Harvard &‬ Smithsonian, the University of Chicago, the East Asian Observatory, the Goethe University‬ Frankfurt, the Institut de Radioastronomie Millimétrique, the Large Millimeter Telescope, the Max Planck‬ Institute for Radio Astronomy, the MIT Haystack Observatory, the National Astronomical Observatory of‬ Japan, the Perimeter Institute for Theoretical Physics, and the Radboud University.‬‬

The EHT array operating at 1.3 mm wavelength included 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 (KP), and the Greenland Telescope (GLT). EHT data were post-processed at the MPIfR correlator facility as well as at the MIT/Haystack Observatory in Westford, MA, USA.

Following forty individuals affiliated to the MPIfR are coauthors in this publication: Walter Alef, Rebecca Azulay, Uwe Bach, Anne-Kathrin Baczko, Silke Britzen, Gregory Desvignes, Sergio A. Dzib, Ralph P. Eatough, Sebastiano D. von Fellenberg, Christian M. Fromm, Michael Janssen, Ramesh Karuppusamy, Joana A. Kramer, Michael Kramer, Thomas P. Krichbaum, Jun Liu, Andrei P. Lobanov, Ru-Sen Lu, Nicholas R. MacDonald, Nicola Marchili, Karl M. Menten, Cornelia Müller, Hendrik Müller, Dhanya G. Nair, Georgios Filippos Paraschos, Alexander Plavin, Eduardo Ros, Helge Rottmann, Alan L. Roy, Saurabh, Tuomas Savolainen, Lijing Shao, Pablo Torne, Efthalia Traianou, Jan Wagner, Robert Wharton, Gunther Witzel, Jompoj Wongphexhauxsorn, J. Anton Zensus, and Guang-Yao Zhao. 

This research received funding from the European Union's Horizon 2020 research and innovation programme under grant agreements RadioNet (No 730562) and M2FINDERS (No 101018682), as well as funding from the European Research Council (ERC) under the Seventh Framework Programme via the Synergy Grant "BlackHoleCam: Imaging the Event Horizon of Black Holes" (Grant No 610058).