Black holes are some of the strangest objects in space. These balls of dense matter are scattered throughout the Milky Way and have gravitational fields so powerful that nothing can escape their gaping mouths – not even light. While we can’t see a black hole head-on as we would a star or a planet, we learn a lot from watching how they affect the fabric of space around them. Now, astronomers have discovered something about these cosmic enigmas that has changed our understanding of them.
In a new study published May 5 in The Astrophysical Journal, an international team of astrophysicists has found that black holes can change the direction of their magnetic fields. This spontaneous reversal was noticed when a black hole in a galaxy 236 million light-years away suddenly became 100 times brighter before calming down. This discovery could mean that black holes are much more dynamic in nature than previously thought – and could even help us find more black holes exhibiting the same behavior.
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When a black hole sucks in gas and dust from the galaxies around it, these materials spin and fall into it and gather to form a spinning disk that generates radiation that scientists can see billions of light-years away.
Because space gas and dust also carry magnetic charges, they give the disks a magnetic field that surrounds the black hole in a specific direction, just like the magnetic fields around Earth point north. The directionality of the magnetic field is believed to influence how gases, planets and other objects fall into a black hole.
In late 2017, astronomers noticed that a specific black hole, dubbed 1ES 1927+654, had grown super bright, peaking and emitting more visible and much more ultraviolet light in May 2018. Its X-ray radiation, too was being affected.
“Usually, if the ultraviolet goes up, so will your X-rays,” Nicolas Scepi, co-author of the new study and a postdoctoral researcher at JILA, a joint research institute between the University of Colorado Boulder and the National Institute of Standards and Technology , said in a press release. “But here, the ultraviolet went up, while the X-ray went down a lot. This is very unusual.”
“Rapid changes in visible and ultraviolet light have been seen in a few dozen galaxies similar to this one,” said Sibasish Laha, research scientist at NASA’s Goddard Space Flight Center, in a press release released by the space agency. “But this event marks the first time we’ve seen X-rays completely falling off while the other wavelengths lighten up.”
In October 2018, the black hole’s X-ray radiation returned. Later, in 2021, everything returned to pre-super bright light conditions. All of this has made researchers realize that they may have stumbled upon something unique and previously unobserved in the cosmos: a black hole has reversed its magnetic field.
“A magnetic reversal, where the north pole becomes south and vice versa, seems to fit the observations better,” Mitchell Begelman, an astrophysicist at CU Boulder and co-author of the study, said in the press release.
The researchers propose that it happened like this: when the black hole sucked in gases with magnetic charges opposite to its own, the magnetic field in one direction got so weak that it shifted in the other direction like a game of tug-of-war.
This new discovery provides a better view of how black holes generate radiation. It could also help us locate more black holes, which have proven elusive despite tens of millions of them likely dotting the Milky Way, observing and analyzing any other super-bright radiation events that show up on our cosmic radar.
“Maybe there are some similar events that have already been observed,” Scepi said. “We just don’t know about them yet.”
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