Magnetar 1E 1547.0-5408 Shows Strongest Evidence of Vacuum Birefringence
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NASA's IXPE telescope measured polarized X-rays from magnetar 1E 1547.0-5408 that stayed aligned with the star's magnetic field as it rotated. The polarization reached 82% at some phases, the strongest observational case yet for vacuum birefringence. The findings appear in a peer-reviewed Nature paper published on 5 August 2026.
Key Facts
- IXPE observed 1E 1547.0-5408 for more than 140 hours between 26 March and 5 April 2025.
- The phase-averaged polarization degree was 46 ± 4% across the 2–8 keV band, rising to 59 ± 5% in the 2–3 keV band.
- At some rotational phases the polarization reached 82 ± 15% and stayed at least about 40% through the radio-beam phase.
- The magnetar's dipole field is estimated at about 2 × 10^14 gauss, roughly 400 trillion times Earth's surface field.
- The Nature paper was published on 5 August 2026 by Rachael Stewart, Hoa Dinh Thi and colleagues.
The Observation
NASA's Imaging X-ray Polarimetry Explorer (IXPE) observed magnetar 1E 1547.0-5408 for more than 140 hours between 26 March and 5 April 2025. NASA's NICER instrument measured the star's X-ray spectrum and timing, while Murriyang, CSIRO's 64-metre Parkes radio telescope, followed its radio pulses. The magnetar completes one rotation in about 2.09 seconds, allowing the team to sort photons by rotational phase and energy. Across IXPE's 2 to 8 kiloelectronvolt band, the phase-averaged polarization degree was 46 ± 4 per cent. It rose to 59 ± 5 per cent in the softer 2 to 3 kiloelectronvolt band, and at some rotational phases reached 82 ± 15 per cent.
Magnetic Field Strength
Magnetars are neutron stars whose magnetic fields exceed 10^14 gauss. The Nature paper uses a dipole-field estimate of about 2 × 10^14 gauss for 1E 1547.0-5408, equivalent to roughly 20 billion tesla. Earth's surface field is about 0.5 gauss on average, making the magnetar's estimated field about 400 trillion times stronger. It also exceeds the quantum-electrodynamic critical field of roughly 4.4 × 10^13 gauss, the scale at which strong-field quantum effects become difficult to ignore.
Quantum Interpretation
In classical electromagnetism, an ideal vacuum has no material structure and does not care how a light wave is polarized. Quantum electrodynamics gives the vacuum a more complicated description, allowing effects such as vacuum birefringence. The interpretation invokes vacuum birefringence, a quantum-electrodynamic effect first described by Werner Heisenberg and Hans Heinrich Euler in 1936. This is one study, not settled consensus: IXPE directly measured the polarized X-rays, but vacuum birefringence is the explanation inferred from those data and from models of how the radiation crossed the magnetar's atmosphere and magnetic field.
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Magnetar 1E 1547.0-5408 Shows Strongest Evidence of Vacuum Birefringence
