admin Black holes are powerful powers in space. They provide quasars and other active galactic nuclei with the energy they need to shine (AGN). That’s because of the way matter and its massive gravitational and magnetic forces work together.
Technically, a black hole has no magnetic field, unlike the dense plasma that makes up the accretion disk that surrounds it. As the plasma twists around the black hole, the charged particles inside create electric currents and magnetic fields. Since the direction of the plasma flow does not change on its own, it is likely that the magnetic field is quite stable. Imagine how surprised scientists were when they found evidence that the black hole’s magnetic field had changed direction.
One way to think of a magnetic field is like a magnet with north and south poles. When the direction of the imaginary pole and the magnetic field both change, it is called magnetic inversion. That’s normal for stars. Scientists have known about the 11-year cycle of sunspots since the 1600s. This cycle is caused by the Sun’s magnetic field changing direction every 11 years. Even the Earth’s magnetic field changes direction every few hundred thousand years or so. But supermassive black holes are not thought to be susceptible to magnetic inversion.
In 2018, a computer scan of the sky revealed a sudden change in a galaxy 239 million light-years away. The galaxy 1ES 1927+654 is now 100 times brighter than before.
Soon after its discovery, the Swift Observatory caught it emitting X-rays and ultraviolet rays. Archives from the region show the galaxy starting to get brighter in late 2017.
At the time, it was thought that the sudden brightening was caused by a star moving near the supermassive black hole at the center of the galaxy. A close encounter like this would trigger a tidal perturbation event, shattering the star and preventing gas from flowing into the black hole’s accretion disk. However, new research makes this theory less likely to come true.
The scientists looked at data on cosmic flares across the entire spectrum of light, from radio waves to X-rays. One thing they noticed was that the X-ray’s power was rapidly decreasing. X-rays are usually emitted when charged particles move through a strong magnetic field, meaning that the magnetic field around the black hole has changed rapidly.
At the same time, visible and ultraviolet light became brighter, indicating that parts of the black hole’s accretion disk were becoming hotter. These would not happen if there was a tidal disturbance.
Instead, magnetic inversion is the best way to interpret the results. The researchers showed that when a magnetic reversal occurs in the accretion disk of a black hole, the magnetic field first weakens near the edges of the disk. As a result, the disc can heat up faster. When the magnetic field is weaker, the charged particles emit less X-rays. When the magnetic field is restored, the disk will return to the way it was.
This is the first time we have seen the magnetic field of a galactic black hole. We know these changes can happen, but we don’t know how often they happen. More research is needed to determine how many times a galaxy’s black hole can change position.
