A rare and enigmatic outburst from an active galaxy 236 million light-years away may have been sparked by a magnetic reversal, a spontaneous flip of the magnetic field surrounding its central black hole.
The NASA team opines that the eruption’s unusual characteristics are linked to changes in the black hole’s vicinity, suggesting a magnetic flip.
The theory detailed in the study, titled “A radio, optical, UV and X-ray view of the enigmatic changing look Active Galactic Nucleus 1ES~1927+654 from its pre- to post-flare states” published in The Astrophysical Journal, describes an unusual characteristic of an eruption linked to the changes in the vicinity of the black hole.
“Rapid changes in visible and ultraviolet light have been seen in a few dozen galaxies similar to this one,” said Sibasish Laha, a research scientist at the University of Maryland, Baltimore County and NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “But this event marks the first time we’ve seen X-rays dropping out completely while the other wavelengths brighten.”
Scientists analyzed telescopes for their research in which they noticed in 2018 that the galaxy called 1ES 1927+654 had brightened almost a hundred times. Archive data suggests that the galaxy’s eruption started near the end of 2017, but observations were only made in June 2018, when higher-energy X-ray emissions had disappeared completely.
Although a previous theory about the explosion suggests it was triggered by a star destroyed by the black hole, researchers have suggested another possible scenario.
Study co-author Mitchell Begelman from the University of Colorado-Boulder said that a magnetic reversal in which the north pole and south pole switch seems to be the best fit for observation of the explosion. Per Space.com, visible and UV light should increase toward the galaxy’s center if a magnetic reversal occurs that causes the north pole to become the south pole and vice versa.
Magnetic field reversals are common occurrences in space. Every 11 years, the Sun switches north and south poles as part of a cycle tied to a string of massive solar eruptions observed recently.
Additionally, the magnetic field weakens so much that the corona cannot be supported anymore and so X-ray emissions cease and only re-emerges in October 2018, roughly four months after it disappeared, which suggests a magnetic reversal happened. This means that X-ray emissions returned and corona had been restored after the flip.
The team used two space telescopes to complete their observation that tracks changes in ultraviolet and X-rays. These telescopes are NASA’s Neil Gehrels Swift Observatory and the XMM-Newton satellite of ESA. They conducted several ground-based visible light and radio observations in various locations, like Italy, the Canary Islands, and New Mexico.
The research team analyzed new and archival observations across the spectrum. NASA’s Neil Gehrels Swift Observatory and ESA’s (European Space Agency) XMM-Newton satellite provided UV and X-ray measurements.
Visible light observations came from Italy’s 3.6-meter Galileo National Telescope and the 10.4-meter Gran Telescopio Canarias, both located on the island of La Palma in the Canary Islands, Spain. Radio measurements were acquired from the Very Long Baseline Array, a network of 10 radio telescopes located across the United States; the Very Large Array in New Mexico; and the European VLBI Network.
“It was very exciting to delve into this galaxy’s strange explosive episode and try to understand the possible physical processes at work,” said José Acosta-Pulido, a co-author at the Canary Islands Institute of Astrophysics (IAC) on Tenerife.
A magnetic reversal, where the north pole becomes south and vice versa, seems to best fit the observations,” said co-author Mitchell Begelman, a professor in the department of astrophysical and planetary sciences at the University of Colorado Boulder.
He and his Boulder colleagues, post-doctoral researcher and co-author Nicolas Scepi and professor Jason Dexter, developed the magnetic model. “The field initially weakens at the outskirts of the accretion disk, leading to greater heating and brightening in visible and UV light,” he explained.
As the flip progresses, the field becomes so weak that it can no longer support the corona – the X-ray emission vanishes. The magnetic field then gradually strengthens in its new orientation. In October 2018, about 4 months after they disappeared, the X-rays came back, indicating that the corona had been fully restored. By summer 2021, the galaxy had completely returned to its pre-eruption state.
Magnetic reversals are likely to be common events in the cosmos. The geologic record shows that Earth’s field flips unpredictably, averaging a few reversals every million years in the recent past. The Sun, by contrast, undergoes a magnetic reversal as part of its normal cycle of activity, switching north and south poles roughly every 11 years.
