This illustration shows the accretion disk, corona (pale, conical swirls above the disk), and supermassive black hole of active galaxy 1ES 1927+654 before its recent flare-up. Credit: NASA/Sonoma State University, Aurore Simonnet
NASA’s Swift Observatory Tracks Potential Magnetic Flip of Monster Black Hole
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
Explore the unusual eruption of 1ES 1927+654, a galaxy located 236 million light-years away in the constellation Draco. A sudden reversal of the magnetic field around its million-solar-mass black hole may have triggered the outburst. Credit:
This sequence illustrates various features of galaxy 1ES 1927+654’s outburst, from its dramatically increased brightness in visible and UV to the loss and recovery of the corona, the source of high-energy X-rays. Credit: NASA’s Goddard Space Flight Center
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.
In early March 2018, the All-Sky Automated Survey for Supernovae alerted astronomers that a galaxy called 1ES 1927+654 had brightened by nearly 100 times in visible light. A search for earlier detections by the NASA-funded Asteroid Terrestrial-impact Last Alert System showed that the eruption had begun months earlier, at the end of 2017.
This diagram illustrates the magnetic reversal interpretation of the eruption at the center of the active galaxy known as 1ES 1927+654. Yellow lines depict the initial direction of the magnetic field, while orange lines indicate the reversed polarity. In late December 2017, the accretion disk brightened up by to 100 times in visible light, a result of increased “feeding” by the supermassive black hole – possibly triggered by a change of magnetic polarity in the outer disk. In August 2018, the reversed magnetic flux reached the inner accretion disk, causing the corona – and the high-energy X-rays it produced – to vanish. In October 2018, the X-rays returned, indicating that the corona had been rebuilt, but it gradually became more intense, reaching a peak in November 2019. During this period, the magnetic field strengthened in its new orientation, and a higher flow of matter could reach the black hole. Present day: The black hole has settled into its 2011 pre-eruption state, but with a magnetic field of opposite polarity. Credit: NASA’s Goddard Space Flight Center/Jay Friedlander
When Swift first examined the galaxy in May 2018, its UV emission was elevated by 12 times but steadily declining, indicating an earlier unobserved peak. Then, in June, the galaxy’s higher-energy X-ray emission disappeared.
“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.
This video illustrates the magnetic reversal interpretation of the eruption at the center of the active galaxy known as 1ES 1927+654, as shown in the diagram above. Credit: NASA’s Goddard Space Flight Center/Jay Friedlander
Most big galaxies, including our own
“An earlier interpretation of the eruption suggested that it was triggered by a star that passed so close to the black hole it was torn apart, disrupting the flow of gas,” said co-author Josefa Becerra González, also at the IAC. “We show that such an event would fade out more rapidly than this outburst.”
Illustration of the Neil Gehrels Swift Observatory. Credit: NASA
The unique disappearance of the X-ray emission provides astronomers with an important clue. They suspect the black hole’s magnetic field creates and sustains the corona, so any magnetic change could impact its X-ray properties.
“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.
Reference: “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” by Sibasish Laha (NASA-GSFC), Eileen Meyer, Agniva Roychowdhury, Josefa Becerra González, J. A. Acosta-Pulido, Aditya Thapa, Ritesh Ghosh, Ehud Behar, Luigi C. Gallo, Gerard A. Kriss, Francesca Panessa, Stefano Bianchi, Fabio La Franca, Nicolas Scepi, Mitchell C. Begelman, Anna Lia Longinotti, Elisabeta Lusso, Samantha Oates, Matt Nicholl and S. Bradley Cenko, Accepted, The Astrophysical Journal.
arXiv:2203.07446
Goddard manages the Swift mission in collaboration with Penn State, the Los Alamos National Laboratory in New Mexico, and Northrop Grumman Space Systems in Dulles, Virginia. Other partners include the University of Leicester and Mullard Space Science Laboratory in the United Kingdom, Brera Observatory in Italy, and the Italian Space Agency.