A runaway pulsar’s 37-light-year wake is not one simple jet

A neutron star racing through the Milky Way leaves more than one line behind it. Around PSR J1101-6101, better known as the Lighthouse pulsar, one X-ray feature reaches across roughly 37 light-years. A shorter trail points back towards the remains of the stellar explosion that made the pulsar. The two structures look dramatic in a composite image, but their geometry has been difficult to explain.

A new polarization study turns those streaks into a rough map of magnetic direction. NASA’s Imaging X-ray Polarimetry Explorer, or IXPE, observed the Lighthouse system between 30 May and 17 June 2025. The results, published in *The Astrophysical Journal* on 9 July 2026, support the idea that the longest, narrowest filament is made by very energetic particles escaping the pulsar’s bow shock and following the Milky Way’s magnetic field.

That is a more precise claim than saying the pulsar simply fires a jet. The object is moving through interstellar gas at high speed. Like water piling up around the bow of a boat, gas and particles form a shock ahead of it. Most particles are expected to remain in the turbulent wake, producing the shorter trail. Some of the highest-energy electrons and positrons appear able to break out and stream along the surrounding galactic field, drawing the long filament in X-rays.

Researchers have discussed that escape route since 2008. The new test relies on polarization, a property that records the preferred orientation of light’s electric field. X-rays made by charged particles spiralling around magnetic field lines can be polarized. From that alignment, astronomers can infer the projected direction of the field and estimate how ordered or turbulent it is.

The measurement was not easy. The Lighthouse Nebula is faint, and IXPE does not make the same kind of sharply detailed image as NASA’s Chandra X-ray Observatory. The team combined IXPE’s polarization sensitivity with Chandra’s spatial map, pulse timing and statistical weights designed to separate the pulsar, trail, filament and background. The paper describes about 950,000 seconds of usable IXPE exposure, close to 11 days of accumulated observing time within the longer calendar window.

For the filament, the study reports a polarization degree of 55 per cent, with an uncertainty of 18 percentage points. Its inferred magnetic field runs along the filament. The detection reaches the 99 per cent confidence threshold, and NASA says the field-flow alignment is supported at greater than 99 per cent confidence. That is strong evidence for the proposed route, but it is not an infinitely sharp map. The paper notes that the polarization detection is not at the conventional three-sigma level, partly because data from one IXPE detector unit were unavailable.

The strength of the polarization also creates a complication. A highly polarized signal usually means the magnetic field remains fairly ordered rather than being scrambled by strong turbulence along the line of sight. Some models expected particles escaping the pulsar to amplify turbulence until it became much stronger than the background field. The IXPE result instead favours a less disturbed field in the part of the filament that was measured. It does not end the modelling argument, but it removes the comfort of treating turbulence as an adjustable explanation for everything.

The shorter trail produced the stranger contrast. Its X-ray polarization indicates a magnetic field running along the trail. Radio observations from the Australia Telescope Compact Array point almost perpendicular to that direction. Those measurements are not necessarily contradictory because radio and X-ray emission can come from particles with different energies occupying different regions of the wake.

That makes the system less like a single luminous hose and more like layered traffic. Faster, higher-energy particles radiating X-rays may trace one part of the magnetic structure, while lower-energy particles visible in radio follow another. The study’s authors say the mismatch is the first clear indication in this object that separate particle populations occupy distinct regions, potentially involving different acceleration mechanisms.

There is useful restraint in the result. The image combines several instruments and assigns colours to wavelengths that human eyes cannot see. IXPE has not photographed magnetic field lines directly, nor has it watched individual particles travel for 37 light-years. The conclusion comes from the statistical orientation of X-ray light, interpreted through synchrotron physics and checked against Chandra and radio maps.

The Lighthouse name can also mislead. The pulsar spins about 16 times each second, but the long feature is not a beam sweeping across Earth like a maritime lamp. It is a structure in the surrounding nebula, shaped by a compact remnant moving through gas and magnetic fields about 21,000 light-years away, according to the latest Chandra release.

What IXPE adds is not merely another colour in a striking picture. It provides a way to test which line is a trapped wake, which is an escape path, and how much disorder lies inside each. In this case, the magnetic map confirms one old idea and unsettles another. The particles seem to follow the long filament as predicted, but the field is calmer, and the shorter trail more internally divided, than the simplest versions of the story allowed.