Pulsar used to measure magnetic field of Milky Way’s black hole

Nature : The supermassive black hole Sagittarius A*, at the heart of the Milky Way, is much fainter than a black hole of its size is expected to be. Observations of a recently discovered pulsar in orbit around Sagittarius A* have revealed that the black hole has a magnetic field 100 times as strong as Earth’s. The surprisingly strong magnetic field would significantly reduce the speed of material falling toward the black hole’s event horizon. Heino Falcke of Radboud University in Nijmegen, Netherlands, and his colleagues were using the 100-metre Effelsberg Radio Telescope near Bonn, Germany, to study a newly discovered magnetar—a rare type of pulsar with a magnetic field 100 trillion times the strength of Earth’s. The magnetar appeared to be orbiting Sagittarius A*, and they hoped to use it to measure the black hole’s gravitational effect on the curvature of space. They discovered that the magnetar was 20 000 AU away from the black hole, too far to measure relativistic effects. However, they found that the radio waves from the magnetar were twisted into corkscrew shapes by the black hole’s magnetic field. Because the effect was different at different wavelengths, they were able to estimate the magnetic field strength