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Scientists detect the magnetic field that powers our galaxy’s supermassive black hole

In this artist's conception, the black hole at the center of our galaxy is surrounded by a hot disk of accreting material. Blue lines trace magnetic fields. (M. Weiss/CfA)

The Milky Way, like most galaxies, has a supermassive black hole sitting right in its center. Now, for the first time, scientists have detected a magnetic field just outside the event horizon — or outer boundary — of that black hole. Why do we care? Because that magnetic field is probably what makes our neighborhood black hole so powerful.

This is what it looks like when a black hole tears a star apart

It shouldn't come as a surprise to you that black holes "suck" stars in and tear them apart. But the process doesn't actually work as simply as vacuuming up some dust. Lots of matter is able to orbit the black hole at a safe distance, creating a flat disk full of all sorts of cosmic goodies. But this so-called accretion disk is magnetized, and the hot, turbulent conditions cause all sorts of wonky interactions between the different magnetic fields. These interactions are thought to be critical to the black hole's ability to acquire matter — and to its ability to turn that matter into intense radiation that jets into space, shaping surrounding galaxies.

"Understanding these magnetic fields is critical. Nobody has been able to resolve magnetic fields near the event horizon until now," Michael Johnson of the Harvard-Smithsonian Center for Astrophysics, the lead author of a paper on the findings published Thursday in Science, said in a statement.

Scientists just caught a black hole swallowing a star — and burping a bit back out

To find evidence of these magnetic fields around Sagittarius A, the black hole at the center of our galaxy, scientists needed a telescope as big as Earth itself. Well, not telescope, exactly: They used the Event Horizon Telescope (EHT), which is a network of radio telescopes across the globe. When you put all those radio telescopes together into one massive array, you can see some really hard to spot stuff — including compact black holes.

"We are on the cusp of a true first in astronomical exploration," study author Avery Broderick of the Perimeter Institute for Theoretical Physics and the University of Waterloo said in a statement. "We fully expect to have imaged a black hole's event horizon in a matter of years. This would be an incredible accomplishment, not just for science, but humankind."

The researchers looked for light that was polarized in a particular way — the signature left behind by a magnetic field. By looking for this signature, they could trace the structure of the magnetic field itself. They found that some regions of the event horizon had patterned, orderly magnetic fields, while others were a jumbled mess. Further research will help scientists determine which parts of the field are responsible for the high-energy jets that black holes emit.

"Once again, the galactic center is proving to be a more dynamic place than we might have guessed," Johnson said in a statement. "Those magnetic fields are dancing all over the place."

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