Magnetar Observations Reveal Light’s Hidden Birefringence in Vacuum
Astronomers using multiple instruments observed magnetar 1E 1547.0−5408 and found polarization patterns consistent with vacuum birefringence, a quantum-electrodynamics effect where light splits in polarization under extreme magnetic fields. The result, aligning with Heisenberg–Euler predictions, provides strong observational evidence that empty space can modify light’s speed and polarization in ultra-strong magnetic environments, one of the clearest demonstrations of quantum vacuum properties to date.