How this happens is not well understood, although it is thought that strong magnetic fields, acting very close to the event horizon, play a crucial part in this process, helping the matter to escape from the jaws of darkness.
Up to now only weak magnetic fields far from black holes - several light-years away - had been probed. In this new study, however, astronomers from Chalmers University of Technology and Onsala Space Observatory in Sweden have now 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 boosted away from the black hole in the form of a 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.
"Polarisation is an important property of light and is much used in daily life, for example in sun glasses or 3D glasses at the cinema," said lead author Ivan Marti-Vidal, according to the press release. "When produced naturally, polarisation can be used to measure magnetic fields, since light changes its polarisation when it travels through a magnetised medium. In this case, the light that we detected with ALMA had been travelling through material very close to the black hole, a place full of highly magnetised plasma."
"We have found clear signals of polarisation rotation that are hundreds of times higher than the highest ever found in the Universe," said co-author Sebastien Muller, according to the press release. "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."
This research was presented in a paper entitled "A strong magnetic field in the jet base of a supermassive black hole" to appear in the journal Science on April 17.