NASA’s IXPE captures first direct evidence of vacuum birefringence

NASA’s IXPE (Imaging X-ray Polarimetry Explorer) may have captured the first direct evidence of vacuum birefringence, a 90-year-old prediction of quantum electrodynamics, according to a study published in Nature on August 5, 2026.

The evidence comes from more than 140 hours of observations of magnetar 1E 1547.0-5408, a rapidly spinning neutron star with magnetic fields over a trillion times stronger than Earth’s, gathered between March and April 2025.

Coordinated measurements by NASA’s NICER telescope and CSIRO’s Murriyang radio telescope made this the first simultaneous radio and X-ray polarization study of a magnetar.

The data revealed X-ray polarization nearly three times higher than standard surface emission models predict. The magnetar’s magnetic geometry would normally suppress polarization to near zero at certain rotation phases, making this smoothly varying, high polarization a striking anomaly.

Researchers attribute the signal to vacuum birefringence, first theorized in 1936. The concept holds that extreme magnetic fields alter the vacuum, turning it into a prism that filters light by its direction and amplifies polarization.

Simulations co-led by Hoa Dinh Thi, a postdoctoral associate at Rice University, show that reproducing the observed X-ray polarization while matching radio constraints requires vacuum birefringence in the neutron star’s environment.

“This result truly highlights the interdisciplinary power of astrophysics,” said Rachael Stewart, a Ph.D. candidate at George Washington University and the study’s lead author. “The information from this distant star core gives us clues about the nature of the fabric of reality.”

Further IXPE observations of this magnetar and others are planned to confirm the signal and potentially uncover additional exotic effects of quantum electrodynamics.

IXPE is a joint mission between NASA and the Italian Space Agency, led by NASA’s Marshall Space Flight Center.