For the first time, astronomers have directly measured the magnetic field of a rapidly spinning pulsar known as PSR J1101−6101, at the heart of the so-called Lighthouse Nebula. Using NASA's Imaging X-ray Polarimetry Explorer (IXPE), the team confirmed a long-standing idea about how these extreme objects fling particles across space – while turning up a surprise about the magnetism itself. The results appear in The Astrophysical Journal.
A pulsar is the collapsed core of a massive star: a neutron star packing more mass than the Sun into a sphere the size of a city, wielding an intense magnetic field. This one whirls 16 times every second, sweeping beams across the sky like a lighthouse.
Chasing particles at nearly light speed
Two narrow streamers of X-rays extend from the pulsar – a longer "filament" and a shorter "trail." Since 2008, researchers had suspected that the most energetic particles escape the system along the galaxy's magnetic field lines, drawing out the filament. To test the idea, IXPE spent nearly 18 days trained on the faint nebula in June 2025.
"The 'smoking gun' would come by measuring the polarization of the light, which indicates the magnetic field direction," said Jack Dinsmore, the Stanford University undergraduate who led the study. The effort paid off: with better than 99% confidence, the magnetic field lines up with the flow of particles along the filament, confirming the escape route.
The data also held a twist. Many models assume the filament's magnetic field is highly turbulent, but the strong, orderly polarization the team measured points to far calmer conditions. "The high polarization degree we measured indicates lower turbulence than such models require," said Stanford professor Roger Romani, a co-author. Adding to the puzzle, the X-ray measurements placed the field parallel to the trail, while radio observations of the same structure showed it running almost perpendicular.
To capture the faint signal, IXPE scientists built new analysis tools that wring information from every photon – methods that could sharpen future studies of neutron stars, natural laboratories for physics no lab on Earth can recreate. Each such measurement chips away at how matter behaves under the most extreme conditions known.