Magnetic Flip Seen Around First Photographed Black Hole Pushes “Models To The Limit”

The first image of a black hole was of M87*, the supermassive monster at the center of the enormous elliptical galaxy M87. The image was only possible thanks to the Event Horizon Telescope, and follow-up observations have revealed more insight, including information about its magnetic field. Researchers have now seen that it is changing quite a lot.

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Magnetic fields in space can be measured by studying the polarization of light, the way light oscillates in specific directions as it travels towards us. 3D film used glasses and polarized light to project two different images to our eyes. Similarly, a strong magnetic field can affect light, creating a polarization pattern that can be seen from across the universe.

M87 is not that far, all things considered, just 55 million light-years away. The supermassive black hole M87* sits at its center and weighs about 6 billion times the mass of the Sun. The EHT saw the polarization of the plasma around it in 2017, 2018, and 2021. It was first swirling one way, then it seemed stable, and in the latest observations, it is going the opposite way.

"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," co-lead author Paul Tiede, from the Center for Astrophysics, Harvard & Smithsonian, said in a statement. "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 fact that the polarization pattern flipped direction from 2017 to 2021 was totally unexpected,” added 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.”

M87* produces a jet of material that extends for up to 5,000 light-years. It is made of particles accelerated to almost the speed of light. Studying the magnetic properties of M87* gives an insight into the formation of such a jet, a process that remains mysterious.

"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," explained Eduardo Ros from the Max Planck Institute for Radio Astronomy (MPIfR) in another statement. "Since M87*'s jet emits across the entire spectrum – from radio waves to gamma rays and neutrinos – it provides a unique laboratory for investigating how such extreme cosmic phenomena form and are launched."

The Event Horizon Telescope works by leveraging a fantastic technique called interferometry. By using telescopes spread across the surface of the planet, all measuring the same object at the same time, it is like researchers are using a single telescope as big as the Earth. In the 2021 measurements, there were two new telescopes (Kitt Peak in Arizona and NOEMA in France) and others had received upgrades, making the measurements even better.

“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 Radboud University Nijmegen, also affiliated to the MPIfR. "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."

The study is published in the journal Astronomy & Astrophysics.