A black hole might have reversed its magnetic field right before our eyes.
The story begins with a galaxy known as 1ES 1927+654, which briefly ceased X-ray emissions for a few months, then resumed and increased. So far, the potential black hole observations represent a unique situation visible from 236 million light-years away.
"This event marks the first time we've seen X-rays dropping out completely while the other wavelengths brighten," study lead author Sibasish Laha, a research scientist at the University of Maryland, Baltimore County and NASA's Goddard Space Flight Center in Maryland, said in a NASA statement (opens in new tab).
If scientists can confirm that the outburst was due to a supermassive black hole at the heart of the galaxy changing its magnetic field, the event may help astrophysicists understand how such a switch affects the black hole's environment, according to the statement.
The Milky Way (and most other large galaxies like it) have a supermassive black hole embedded at its heart; the black hole pulls matter in toward its center. The matter first collects in an accretion disc surrounding the black hole, then heats up and emits light (in visible, ultraviolet and X-ray wavelengths) as the matter is pushed inward.
As that matter pushes inward, it forms a cloud of extremely hot particles that scientists call a corona. The new study suggests that changes in the corona are what caused the X-rays streaming from the heart of galaxy 1ES 1927+654 to temporarily disappear.
If a magnetic reversal took place, causing the north pole to become the south pole and vice versa, visible and UV light should increase toward the center of the galaxy due to more heating, as the corona begins to diminish and the accretion disk grows more compact in the center.
But as the flip evolves, the field weakens so much that the corona cannot be supported at all any more, causing the X-ray emissions to cease, researchers suggested.
That idea matches observations of this galaxy, as the X-ray emissions re-emerged in October 2018, roughly four months after they disappeared, suggesting a magnetic reversal took place. The galaxy returned to pre-eruption X-ray emissions in summer 2021.
Two space telescopes tracked the changes in ultraviolet and X-rays, including NASA's Neil Gehrels Swift Observatory and the European Space Agency's XMM-Newton satellite. Visible light and radio observations were performed from several ground-based telescopes in locations such as Italy, the Canary Islands and New Mexico.
A paper (opens in new tab) based on the research has been accepted for publication in The Astrophysical Journal and is available on preprint service arXiv.org.