A first-of-its-kind measurement of a magnetar may have captured empty space behaving in a way physicists have predicted for 90 years but never directly observed.
In a new study published in the journal “Nature,” an international team of scientists led by Rachael Stewart, a physics Ph.D. candidate at George Washington University, examined more than 140 hours of observations of the magnetar 1E 1547.0-5408.
The results were captured between March and April 2025, primarily using NASA’s IXPE (Imaging X-ray Polarimetry Explorer) mission.
Other instruments involved in the measurements included NASA’s NICER (Neutron Star Interior Composition Explorer), an X-ray telescope attached to the International Space Station; and Murriyang, a radio telescope hosted at the Parkes Observatory in New South Wales and owned and operated by Australia’s national science agency CSIRO.
It was the first-ever coordinated radio and X-ray polarization measurement of a magnetar, a special class of neutron stars with ultra-strong magnetic fields—around a trillion times stronger than the strongest permanent magnets ever built on Earth. These super magnetic neutron stars offer glimpses into the physics of intense environments that cannot be found anywhere else.
“The information we obtained from looking at this distant star core gives us clues about the nature of the fabric of reality as we know it, and I find that to be incredible,” said Stewart, the lead author on the study titled “Vacuum birefringence and the polarized X-ray emission from a radio magnetar.”
Observations showed the polarization—the orientation and level of alignment of the incoming photons—is nearly three times greater than seen in similar sources. The high level of polarization surprised researchers, Stewart noted. The geometry of the magnetar’s magnetic fields suggests that the measurements should be close to zero at certain points in the star. Standard surface emission models do not explain the large value either, indicating that another effect must be boosting the polarization.
Enter vacuum birefringence, a 90-year-old theory in the realm of quantum electrodynamics. First proposed in 1936, the theory suggests that the vacuum of space can be altered by extreme magnetic fields. Under such conditions, the vacuum acts like a lens or a prism, filtering light based on the direction it is traveling, therefore enhancing its total polarization.
The magnetar’s large polarization, measured by the IXPE mission and other instruments, strongly supports the vacuum birefringence theoretical prediction by showing signs that supposedly empty space is altering how light travels. It could be the first time this effect has been directly observed anywhere.
“This result provides an important link in the chain of evidence supporting one of the most successful theories in all of science,” Stewart said.
The study was co-authored by scientists from institutions across several countries, including George Younes, a research professor of physics at GW’s Columbian College of Arts and Sciences (CCAS).
“It is always interesting when scientists manage to find evidence for a theoretical prediction that is very hard to prove, in this case a 90-year-old one,” said Alexander van der Horst, chair of the CCAS Department of Physics. “It is remarkable that one of our graduate students led a joint effort of astronomical observers and theorists to do this as part of her Ph.D. thesis work."
The research involved scientists from the Center for Space Sciences and Technology; the South African Radio Astronomy Observatory (SARAO); the Los Alamos National Laboratory; NASA’s Marshall Space Flight Center; the Center for Research and Exploration in Space Science & Technology (CRESST); the Astrophysics Science Division at NASA’s Goddard Space Flight Center; and other universities around the world.
The results “demonstrate how increasingly collaborative and communal science has become,” Stewart said. “We could not detect an effect so fundamental, which permeates across the entire observable universe, without the progressive steps achieved by generations and teams of scientists across various disciplines.”