Universe Today
Occasionally, when a massive star dies in a supernova, it can leave behind a dense, rapidly spinning core known as a pulsar. These extreme objects are some of the most fascinating in the universe, and are extremely useful for astronomers when measuring distances or navigating the void of space. A new paper from Jack Dinsmore, a graduate student at Stanford, and his co-authors, and published in The Astrophysical Journal, takes a look at some of the features of one of the most famous examples of a pulsar - PSR J1101-6101, commonly known as the Lighthouse pulsar.
The Lighthouse pulsar is relatively young - with a “spin-down” age (a method for calculating how old a pulsar is) of only 63 kyr (kiloyears). Since it’s so young, it’s also extremely high energy, and is rotating 16 times a second. For anyone unfamiliar with pulsar physics, that was not a typo - the entire star remnant rotates every 63 milliseconds. But what is perhaps most fascinating about the Lighthouse pulsar is its linear speed - it is rocketing through the Milky Way at an astonishing 990 kilometers per second. That is also not a typo - this pulsar is likely twice the mass of our Sun, but it’s also probably only about as wide as Manhattan is tall. And it’s traveling through our galaxy at almost 1000 km/second.
As one might expect, that much mass condensed into such a small area and moving that quickly causes some pretty crazy phenomena in its immediate vicinity. As the pulsar plows through the Interstellar Medium (ISM), it creates a massive bow shock in front of it - similar to a bow wave formed in front of a boat. This, in turn, creates two giant glowing X-ray structures that astronomers have been hoping to understand.
Fraser explains what a pulsar is.The Trail is a bright X-ray wake trailing for about one arcminute directly behind the pulsar’s path. It points directly back to its likely birthplace, the supernova remnant known as MSH 11-61A. When looking at it in radio and X-rays, the Lighthouse’s trail extends for around 37 light years, making it one of the longest structures of its kind in the Milky Way.
The Filament isn’t as grandiose, but it is much rarer. It’s an offshoot that extends orthogonally (i.e. at a 90 degree angle) from the Trail itself. While it extends for a comparable length in space, its orientation to us makes its spread even more spectacular, extending over five arcminutes of the sky.
For decades, there has been a clear theory about how each of these structures evolved. The bow shock caused by the pulsar traps most particles, creating the Trail. But the highest energy ones, such as cosmic ray leptons (electrons and positrons) manage to escape. And once they are free, they follow existing magnetic field lines, and up creating the Filament.
Fraser and Dr. Zach Putnam explain how to use pulsars to navigate in space.This theory had never been proved with actual data though, so Dinsmore and his co-authors thought they would collect some using NASA’s Imaging X-ray Polarimetry Explorer (IXPE). Polarization, in this case, would act as a compass pointing toward the local magnetic field’s direction, offering some proof that the Filament particles are following magnetic field lines.
In June 2025, they observed the nebulae for around 18 days (or 950 kiloseconds as they put it, in what is hopefully a nod to Vernor Vinge’s timekeeping system). The results of that observational campaign were a resounding success - they detected the polarization of the filament with 99% confidence, showing that there is an electric vector position angle (EVPA) that shows the magnetic field is parallel to the filament’s axis.
So it sounds like the theory has some merit. But, there were also some surprises lurking in the data. The polarization degree (PD) of the filament was much higher than expected - at 55% ± 18%, which indicates a much lower amount of magnetic turbulence than is required by most modern magnetohydrodynamic models. In fact, the magnetic field around the filament actually seems to be weaker than the background galactic magnetic field, contradicting some of the models.
Another surprise came when looking at the trail. The trail's PD was a more modest 26%, with another magnetic field running parallel to the trail’s axis as expected. However, this was is stark contrast to the orientation of the magnetic field when observed in radio wavelengths by the Australia Telescope Compact Array, which showed the magnetic field running almost perpendicular to the trail itself. This discrepancy lends credence to the idea that pulsar trails have a layered structure, with strong parallel magnetic field lines pushing X-ray emitting highly energetic particles along, while an inner core of turbulent, perpendicular fields plays host to cooler, radio-emitting electrons.
Collecting all this data was no mean feat either. The researchers had to deal with the loss of one of IXPE’s detector units, and develop their own analytical software pipeline known as LeakageLib. But they were rewarded with a valuable contribution to our understanding of how these marvels of the universe work. Pulsars will undoubtedly continue to amaze astronomers, and the general public, for a long time to come.
Learn More:
NASA - NASA Space Telescope Maps Magnetic Fields of ‘Lighthouse’ Pulsar
J.T. Dinsmore et al - IXPE Polarizations of the Lighthouse Pulsar, Trail, and Filament
UT - Pulsars Rewrite the Rules
UT - A Bizarre Pulsar Switches Between Two Brightness Modes. Astronomers Finally Figured Out Why.
