Astronomers from Chalmers University of Technology and Onsala Space Observatory, Sweden, studied supermassive black holes to find out whether they were surrounded by a magnetic field. Supermassive black holes, often with masses billions of times that of the Sun, are located at the heart of almost all galaxies in the Universe. They suck in most of the matter that accretes around them in the form of a surrounding disc. However, researchers have observed that some matter may get propelled away from the center of the black hole at the speed of light as part of a jet of plasma. To find out the cause behind this, the Swedish astronomers used the giant telescope Atacama Large Millimeter/submillimeter Array (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. They telescope detected strong signals of polarization rotation, an indicator of the presence of a strong magnetic field. This new observation will help astronomers to understand the structure and formation of black holes and the high-speed jets of plasma they eject from their poles.