NRL's VLITE confirmed magnetar GPM J1839–10 has been pulsing regularly every 22 minutes

Magnetars are a type of neutron star (incredibly dense stars left over after a supernova explosion) with super powerful magnetic fields. This particular magnetar sends out a pulse of radio waves every 22 minutes like clockwork, and what's even more odd is that, according to what we currently know about these types of stars, it shouldn't be able to send out radio waves at all.

NRL’s VLITE was developed in collaboration with the National Radio Astronomy Observatory in 2014. VLITE operates on the VLA as a stand-alone instrument for ionospheric and astrophysical studies. VLITE’s 18 antennas collect over 6000 hours of data per year, archived at NRL.

Initially, it was implemented to constantly monitor the Earth’s ionosphere to study disturbances that can affect it, such as geomagnetic storms, seismic events, and gravity waves. This constant surveillance can detect transient blips and bursts of radio waves from elusive cosmic sources without continuous observation. Understanding these phenomena may lead astronomers to a better understanding of the Universe.

In 2022, a group of astronomers worldwide found a strange object in space using a different telescope system. They named this object GPM J1839-10. After hearing about this, the team at the Naval Research Laboratory went back and checked their data and found that they had also picked up signals from this object for many years without realizing what they were seeing.

The extraordinary thing about this object, GPM J1839-10, is that it behaves unlike anything we've seen before. “This enigmatic object has been hiding in the data for decades – we just did not know we had to look for it until its discovery by the MWA,” said Dr. Simona Giacintucci, NRL Research Astronomer. "GPM J1839-10 emits a five-minute pulse of radio wavelength emission every 22 minutes, and it's been doing this for at least 33 years," she added.

An exciting find

“Findings like this are exciting because they highlight the gaps in our understanding of the physics of these extreme stars known as magnetars,” said Dr. Tracy Clarke, NRL Research Astronomer and VLITE Project Scientist. “Current understanding says this object should not emit radio waves, yet we are detecting them across several decades and are [unsure] why. That is an exciting mystery,” she added.

Astronomers believe GPM J1839−10 is a rare neutron star with extremely powerful magnetic fields. “Astronomy is one of those bizarre professions where we cannot go to our objects to study them,” Clarke said. “We are interested in how many of these are and where they are. That is directing future research", she said.

You can view the study for yourself in the journal Nature.

Study abstract:

"Several long-period radio transients have recently been discovered, with strongly polarized coherent radio pulses appearing on timescales between tens to thousands of seconds. In some cases, the radio pulses have been interpreted as coming from rotating neutron stars with extremely strong magnetic fields, known as magnetars; the origin of other, occasionally periodic and less-well-sampled radio transients is still debated. Coherent periodic radio emission is usually explained by rotating dipolar magnetic fields and pair-production mechanisms, but such models do not easily predict radio emission from such slowly rotating neutron stars and maintain it for extended times. On the other hand, highly magnetic isolated white dwarfs would be expected to have long spin periodicities, but periodic coherent radio emission has not yet been directly detected from these sources. Here we report observations of a long-period (21 min) radio transient, which we have labelled GPM J1839–10. The pulses vary in brightness by two orders of magnitude, last between 30 and 300 s and have quasiperiodic substructure. The observations prompted a search of radio archives and we found that the source has been repeating since at least 1988. The archival data enabled constraint of the period derivative to <3.6 × 10−13 s s−1, which is at the very limit of any classical theoretical model that predicts dipolar radio emission from an isolated neutron star."