Intense magnetism has been discovered near a supermassive black hole, and scientists hope it can help them better understand these massive inhabitants of the centers of galaxies.
The magnetic field, detected by the Atacama Large Millimeter/submillimeter Array (ALMA), is so powerful scientists say it’s beyond anything previously detected in the core of a galaxy. And the fact that it’s very close to the event horizon of a supermassive black hole is intriguing, providing insight into the structure and formation of these phenomena.
Supermassive black holes are extremely dense objects, often with masses billions of times that of the Sun. They can accumulate huge amounts of matter in the form of a surrounding disc. While most of this matter is fed into the black hole, some can escape moments before capture and be flung out into space at close to the speed of light as part of a jet of plasma.
Magnetic fields, acting very close to the event horizon, have long been suspected to play a part in this process, helping the matter to escape from the clutches of the black hole. But scientists know only very little about this phenomenon. Only weak magnetic fields far from black holes – those located several light-years away – have been studied – that is, until now.
In this study, published in the journal Science, researchers used ALMA to detect signals directly related to a strong magnetic field very close to the event horizon of the supermassive black hole in a distant galaxy named PKS 1830-211. This magnetic field is located precisely at the place where matter is suddenly ejected from the black hole in the form of a high-speed jet.
The team measured the strength of the magnetic field by studying the way in which light was polarized as it moved away from the black hole.
“Polarization is an important property of light and is much used in daily life, for example in sun glasses or 3D glasses at the cinema,” lead author Ivan Marti-Vidal explained in a news release. “When produced naturally, polarization can be used to measure magnetic fields, since light changes its polarization when it travels through a magnetized medium. In this case, the light that we detected with ALMA had been traveling through material very close to the black hole, a place full of highly magnetized plasma.”
What they found was that the direction of polarization of the radiation coming from the center of PKS 1830-211 had rotated.
“We have found clear signals of polarization rotation that are hundreds of times higher than the highest ever found in the Universe,” added Sebastien Muller, a study co-author. “Our discovery is a giant leap in terms of observing frequency, thanks to the use of ALMA, and in terms of distance to the black hole where the magnetic field has been probed — of the order of only a few light-days from the event horizon. These results, and future studies, will help us understand what is really going on in the immediate vicinity of supermassive black holes.”