An international team of astronomers says a dead star known as a magnetar has produced behavior consistent with vacuum birefringence, a phenomenon predicted in 1936 but never directly observed, according to the researchers.
The magnetar, designated 1E 1547-5408, spins once every two seconds and emits both intense X-rays and bright radio waves, according to a specialty publication reporting on the study. Magnetars are neutron stars that pack more mass than the sun into a region only a few miles across, and they generate magnetic fields that can reach trillions of times the strength of Earth's, according to the same reporting.
According to the specialty publication summarizing the researchers' findings, X-ray polarization detected from the magnetar was almost three times stronger than current models had predicted. The study was based on more than 140 hours of observations conducted in 2025 using NASA's IXPE and NICER telescopes along with Australia's Murriyang radio telescope, the publication reported.
Vacuum birefringence, as described by the specialty publication, predicts that a sufficiently powerful magnetic field could alter the vacuum of space itself. Quantum theory holds that the vacuum is filled with fleeting virtual particles, and under a strong enough magnetic field, that vacuum is theorized to behave like an optical filter that changes the polarization of light passing through it.//
Computer simulations run by the team found that the proposed vacuum birefringence effect produced results consistent with both the X-ray and radio observations of the magnetar. Hoa Dinh Thi, a researcher at Rice University and co-lead author of the study, said the team's model suggests that reproducing the observed X-ray polarization signatures while also satisfying constraints from the radio observations requires the presence of vacuum birefringence. Thi also said neutron stars allow scientists to test fundamental physics in extreme environments that cannot be replicated in laboratories on Earth.
The international team described the results as the strongest evidence to date for one of the longest-standing predictions in quantum physics, though the astronomers said vacuum birefringence has never been directly observed before this study. The team said further observations will be needed to confirm the findings, and added that confirmation through future magnetar studies could point to the presence of other exotic phenomena.
The study, titled 'Vacuum birefringence and the polarized X-ray emission from a radio magnetar,' appeared in the journal Nature.