Black holes are powerful. The energy behind quasars is provided by them. The matter interacts with the powerful magnetic fields.
A black hole doesn't have a magnetic field of its own, but it does have a dense plasma surrounding it. The charged particles within the black hole generate an electrical current and magnetic field. The magnetic field is stable because the direction of the flow doesn't change spontaneously. Astronomers were surprised when they saw evidence that a black hole's magnetic field had changed.
A magnetic field can be seen as a simple magnet with a north and south pole. A magnetic reversal is where the orientation of the imaginary pole is different from the magnetic field. The effect is common among stars. Astronomers have observed a cycle of sunspots since the 1600s because our Sun reverses its magnetic field every 11 years. The Earth undergoes magnetic reversals every few hundred thousand years. It was thought that magnetic reversals weren't likely for black holes.
An automated sky survey found a sudden change in the sky. The galaxy had a factor of 100 in visible light. The Swift Observatory captured its glow in x-rays and ultraviolet. A search of archival observations of the region showed that the galaxy began to improve towards the end of last year.
At the time it was thought that this was caused by a star passing close to a black hole. A close encounter would cause a tidal disruption event, which would rip the star apart as well as disrupt the flow of gas in the black hole. The study casts a shadow on that idea.
The team looked at the full spectrum of light from radio to x-ray. The intensity of x-rays dropped off very quickly. A sudden change in the magnetic field near the black hole was suggested by the X-rays being produced by charged particles. The black hole's accretion disk was getting hotter as the intensity of light in visible and ultraviolet increased. The effects are not what you would expect with a tidal disruption event.
A magnetic reversal is better for the data. As a black hole accretion disk undergoes a magnetic reversal, the fields weaken at the outer edges. The disk can heat up more efficiently. Fewer x-rays are produced by charged particles because of the weaker magnetic field. The disk returns to its original state once the magnetic field completes its reversal.
This is the first observation of the magnetic reversal of a black hole. We know they can happen, but we don't know how common they are. It will take more observations to figure out how many times a black hole can become a switch hitter.
There is a radio, optical, UV and X-ray view of the Active Galactic Nucleus 1ES 1927+ 654 from its pre- to post-flare states.
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