Astronomers working with NASA's IXPE space X-ray observatory have obtained what may be the first direct confirmation of vacuum birefringence—a quantum phenomenon whose existence was predicted nearly 90 years ago. The study's results were published in the journal Nature.

Magnetar observations point to unusual vacuum behavior

The research was based on more than 140 hours of observations of the magnetar 1E 1547-5408, conducted in March–April 2025 using the IXPE and NICER space observatories, as well as Australia's Murriyang (Parkes) radio telescope. This marked the first-ever coordinated measurement of the radio and X-ray polarization of a magnetar.

Magnetars are a special class of neutron stars with magnetic fields more than a trillion times stronger than Earth's. Neutron stars themselves are the ultra-dense remnants of massive stars following their deaths and serve as natural laboratories for studying extreme physics.

The object 1E 1547-5408 completes a full rotation roughly every two seconds while simultaneously emitting powerful radio and X-ray radiation. Analysis revealed that the polarization degree of its X-ray emissions is nearly triple that observed in similar objects. Existing models of magnetar surface structures cannot account for such high polarization, which researchers believe indicates the presence of an additional physical mechanism.

1936 theory receives potential confirmation

Scientists consider vacuum birefringence—first predicted by quantum electrodynamics in 1936—to be the most likely explanation.

According to this theory, extremely powerful magnetic fields can alter the properties of the vacuum itself. Under such conditions, empty space begins to act like a lens or prism, affecting light differently based on its propagation direction and thereby boosting its polarization.

Computer modeling demonstrated that the presence of this effect cleanly accounts for the observed X-ray polarization while keeping the findings consistent with radio observations.

According to study co-lead Hoa Dinh Thi of Rice University, the data demonstrates that neutron stars allow physicists to test fundamental physical theories under conditions impossible to replicate in Earth-based laboratories.

The authors note that these results represent the most compelling evidence yet for the existence of vacuum birefringence and possibly its first direct observation. They hope to confirm their findings through further IXPE observations of this and other magnetars, which could also lead to the discovery of new quantum effects in extreme cosmic environments.