A Magnetar Study May Have Caught 'Empty' Space Changing Light

Nearly 90 years ago, physicist Werner Heisenberg predicted a quantum effect called vacuum birefringence, in which even "empty" space can change the way light behaves, because a vacuum briefly fills with "virtual particles" that appear and disappear. Despite major advances in nuclear physics since the 1930s and decades of work with particle accelerators, scientists have never confirmed the effect. Now, observations of a magnetar — a rare neutron star with some of the strongest known magnetic fields — may offer the first evidence.

The study was led by Rachael E. Stewart, a graduate student of physics at George Washington University, and published in the journal Nature, with researchers from institutions including the South African Radio Astronomy Observatory (SARAO) and NASA's Goddard Space Flight Center. Theory predicts that an extraordinarily strong magnetic field can make Heisenberg's virtual particles affect light and produce vacuum birefringence. "Detecting vacuum birefringence requires a magnetic field that is over 100 million times stronger than any we've ever made on Earth," said Dr. Marcus Lower of the Center for Astrophysics and Supercomputing at Swinburne University of Technology, who helped lead the observations.

Lower observed the magnetar 1E 1547.0-5408 with CSIRO's Murriyang (Parkes) radio telescope; the data were analyzed on Swinburne's supercomputer and combined with measurements from NASA's Imaging X-ray Polarimetry Explorer (IXPE) and the NICER X-ray telescope on the International Space Station. Tracking the polarization of the magnetar's radio waves as it rotated showed its magnetic and rotational axes are almost aligned, and that it is seen from a nearly pole-on angle — conditions well suited to detecting the effect.

IXPE found the magnetar's X-rays are highly polarized, with that polarization aligned to its magnetic field just as the radio waves were — both considered possible signs of vacuum birefringence. Researchers say more observations and advanced simulations are still needed to confirm whether the signals really come from vacuum birefringence or other physical processes.