Astronomers observe intense magnetic field close to supermassive black hole in distant galaxy

Astronomers have recently observed an intense magnetic field close to supermassive black hole in distant galaxy with the help of the giant telescope Alma.

A team of five astronomers from Chalmers University of Technology have revealed an extremely powerful magnetic field, beyond anything previously detected in the core of a galaxy, very close to the event horizon of a supermassive black hole.

This new observation helped astronomers to understand the structure and formation of these massive inhabitants of the centres of galaxies, and the twin high-speed jets of plasma they frequently eject from their poles.

Up to now only weak magnetic fields far from black holes, several light-years away, had been probed. In this 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 was located precisely at the place where matter was 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.

The astronomers applied a new analysis technique that they had developed to the Alma data and found that the direction of polarization of the radiation coming from the centre of PKS 1830-211 had rotated.

Magnetic fields introduce Faraday rotation, which makes the polarization rotate in different ways at different wavelengths. The way in which this rotation depends on the wavelength tells us about the magnetic field in the region.

The Alma observations were at an effective wavelength of about 0.3 millimetres, the shortest wavelengths ever used in this kind of study. This allows the regions very close to the central black hole to be probed.

Earlier investigations were at much longer radio wavelengths. Only light of millimetre wavelengths can escape from the region very close to the black hole; longer wavelength radiation was absorbed.

The study is published in the journal Science.