As radio waves travel from the pulsar toward Earth, they encounter magnetic fields generated by clouds of gas getting pulled in by the Milky Way’s central supermassive black hole, called Sagittarius A*. The fields twist the radio waves, which initially oscillated in one direction, into corkscrews.
By measuring this twisting effect, the researchers determined that the magnetic field around Sagittarius A* is relatively strong. Roughly 150 light-years from the black hole’s core, the field is only one-hundredth of the strength of the magnetic field around Earth. But the researchers estimate that the field likely strengthens by five orders of magnitude just outside Sagittarius A*’s core.Reference: R. P. Eatough et al. A strong magnetic field around the supermassive black hole at the center of the galaxy. Nature. August 15, 2013. doi:10.1038/nature12499.