Humanity has discovered just 31 magnetic neutron stars, or magnetars, stellar objects with incredible magnetism. New observations of one of these stars report some bizarre never-before-seen behaviors, suggesting that these objects might have a more complex magnetic field than previously thought.
The star is known as Swift J1818.0-1607, or J1818 for short. It was discovered just under a year ago and it has already got plenty of media attention due to it being the fastest and youngest magnetar known, as well as being a pulsar, a pulsating neutron star. To this list of achievements, the new study published in the Monthly Notices of the Royal Astronomical Society adds another one: This is the first magnetar with a misaligned magnetic pole.
J1818 is an incredible object. From the get-go, after its discovery in March 2020, researchers noticed that it was being “radio-loud”, emitting pulsations of radio waves like a pulsar. By the summer, its emissions were alternating between a bright state and a weaker one. In July, the team saw it flicker between a “pulsar-like” state and a more classic “magnetar-like" state.
“This bizarre behaviour has never been seen before in any other radio-loud magnetar,” lead author and Swinburne University graduate researcher Marcus Lower said in a statement. “It appears to have only been a short-lived phenomenon as by our next observation it had settled permanently into this new magnetar-like state.”
The general idea of how magnetars are sees the magnetic field at the opposite end of the star, in a nice north-south pole configuration. The magnetic poles of J1818 instead appear to be found close to each other near the equator, with the southern one dominating the radio emission.
“From our observations, we found that the magnetic axis of J1818 isn’t aligned with its rotation axis,” said Lower. “Instead, the radio-emitting magnetic pole appears to be in its southern hemisphere, located just below the equator. Most other magnetars have magnetic fields that are aligned with their spin axes or are a little ambiguous.”
The findings are also matched by other research that looked at the magnetar in wavelengths beyond radio. X-ray observations have highlighted a single magnetic distortion. This could be two small but closely spaced poles as the radio observations appear to suggest.
The team plans to keep this star under constant monitoring to see any other changes to the magnetic field. Further studies might lead to something unique: mapping the magnetic field of a magnetar for the first time.