A transient radio source some 4,000 light-years from Earth poses a mystery: for a few hours, it emits highly polarized radio waves every 18 minutes for around 30 to 60 seconds, only to fall silent for a longer period of time. The group led by Natasha Hurley-Walker from Australia’s Curtin University and the International Center for Radio Astronomy Research ICRAR suspects that the radio source is a neutron star with an extremely strong magnetic field. A strongly magnetized white dwarf cannot be ruled out either, as the team reported in »Nature«.
The unusual radio source GLEAM-X J162759.5-523504.3 in the constellation Norma was discovered using the Murchison Widefield Array (MWA) in Australia, a system of radio telescope antennas used to monitor the entire sky accessible there. There, doctoral student Tyrone O’Doherty noticed the radio source when he was trying out a new evaluation program he had developed.
Transient radio sources are not uncommon in and of themselves, but they either last for weeks or months like supernova explosions, or are extremely brief like radio bursts from a pulsar. But a source that’s active for around a minute, then goes silent and lights up again, was previously unknown.
The source was unusually bright and its radiation was highly polarized at 88 percent, meaning the radio waves propagated along a preferred plane of vibration. This indicates a very strong magnetic field at the origin.
“This was totally unexpected,” Hurley-Walker said in a press release. “It was kind of spooky to an astronomer, because there’s nothing in the sky that does that.”
The object could therefore be a theoretically predicted “ultra-long period magnetar”, a slowly rotating neutron star. However, glowing much brighter than predicted, the compact remnant converts magnetic energy into radio waves very efficiently in a way that is still unknown. Hurley-Walker’s group is currently hoping for a reappearance of the object in the sky so that it can be examined in more detail.