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Deep in space, a rapidly spinning neutron star, a pulsar nicknamed the Lighthouse, speeds through tenuous gas. Like a motorboat cutting through water, it leaves a glowing trail of charged particles behind. In X-rays, this trail appears as a bright tail and a thin filament stretching over many light-years.

Pulsars are superdense remnants of exploded stars, rotating dozens of times per second and emitting narrow beams of radiation. When such an object travels through the interstellar medium, it accelerates electrons to nearly the speed of light. These electrons, spiraling around magnetic field lines, emit X-rays, so-called synchrotron radiation. It is akin to the glow of a neon sign, but instead of electricity, the particles are excited by the magnetic field.

Astronomers pointed the IXPE space observatory at the Lighthouse, which can measure the polarization of X-rays. They accumulated a million seconds of observations — nearly 12 days of continuous staring. It turned out that the light from the filament is 55% polarized, and the direction of oscillation indicates that the magnetic field is stretched along the filament, like fibers in a rope. Such high polarization means the magnetic field there is hardly turbulent: it is calm and ordered, not churning as some models suggested.

The scientists also noticed that the X-ray polarization of the tail is nearly perpendicular to the radio polarization. This suggests that the electrons emitting X-rays and those emitting radio waves are in different locations: some closer to the pulsar, others farther away. The pulsar itself is also polarized, and its signal is well described by the rotating vector model — the same one that works for ordinary radio pulsars.

The Lighthouse continues to race through the galaxy, leaving a glowing path behind. Now we know that the magnetic field along this path is not chaotic but aligned like compass needles. This changes our understanding of how pulsars interact with their surroundings and prompts new explanations for such cosmic trails.