Astronomers using NASA’s Imaging X-ray Polarimetry Explorer may have obtained the clearest evidence yet that an intense magnetic field can alter the optical properties of empty space. The peer-reviewed result, published in Nature on Wednesday, concerns the magnetar 1E 1547.0-5408 and a quantum-electrodynamic effect called vacuum birefringence, predicted in 1936 but never directly confirmed.
Magnetars are neutron-star remnants containing more mass than the Sun in an object roughly the size of a city. Their magnetic fields rank as the strongest known in the universe. NASA said 1E 1547.0-5408 completes a rotation about every two seconds and persistently emits radio waves and X-rays, making it unusually suitable for a coordinated test of how light behaves in an extreme field.
Scientists observed the object for more than 140 hours between March and April 2025 with IXPE, alongside NASA’s NICER instrument and Australia’s Murriyang, or Parkes, radio telescope. The campaign produced the first coordinated radio and X-ray polarization measurement of a magnetar. Polarization describes the orientation and alignment of incoming light, and the observed level was nearly three times higher than in comparable sources.
The X-ray polarization reached about 40 percent from one emission region and 80 percent from another, while changing smoothly through the star’s rotation. Standard surface-emission models and the magnetar’s geometry did not account for such strong alignment. The team’s simulations found that reproducing both the X-ray signature and constraints from the radio observations required vacuum birefringence, in which a sufficiently strong magnetic field makes a vacuum act somewhat like a prism and filters light according to direction.
NASA and the researchers described the result as strong support rather than final proof. Further IXPE observations of this magnetar and others are needed to confirm that no competing explanation can reproduce the signal. If verified, the finding would establish a direct astronomical test of a foundational quantum-electrodynamic prediction in conditions impossible to create on Earth, while helping scientists understand neutron-star surfaces, magnetic fields and the behavior of light in extreme environments.
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