Stewart et al. published in Nature this week evidence for vacuum birefringence from X-ray and radio observations of polarized emission from the radio magnetar 1E 1547.0-5408.  The phenomenon of vacuum birefringence, that seemingly empty space can alter the behaviour of light, was predicted nearly 90 years ago by Werner Heisenberg, one of the founding fathers of quantum mechanics.  In the presence of an extremely powerful magnetic field, light can be refracted in specific ways, producing vacuum birefringence. Detecting this effect requires a magnetic field that is over 100 million times stronger than has ever been made on Earth, and the extreme magnetic fields of magnetars are the perfect cosmic laboratories search for this effect.

The team used NASA’s Imaging X-ray Polarimetry Explorer (IXPE), together with the NICER X-ray telescope on the International Space Station and Murriyang, the Parkes radio telescope.  By carefully tracking how the direction the radio waves emitted by the magnetar oscillate as it rotates, the team found the magnetic and rotational axes of 1E 1547.0–5408 are nearly aligned and are viewed almost pole-on. This combination of magnetic and viewing geometry makes this magnetar ideal to look for vacuum birefringence.  The team found two telltale signs that vacuum birefringence is acting around the magnetar: (i) the X-rays produced by the magnetar had extremely high levels of polarisation, and (ii) the polarisation direction was locked to 1E 1547.0–5408’s magnetic field in the same way as the radio waves.  If confirmed, this discovery paves the way for understanding how our theories of quantum physics work in one of the most extreme environments in our universe. The image above is an artist’s impression of a magnetar — a rapidly rotating neutron star with an ultra-strong magnetic field — emitting radio waves and X-rays. (Image credit: NASA/Pablo Garcia)