Astronomers have finally pinpointed the origin of mysterious, repeating radio signals from space, known as long-period radio transients (LPTs). For the first time, researchers have confirmed that these enigmatic bursts, which repeat at intervals ranging from minutes to hours, are coming from a white dwarf actively siphoning material from a companion star.
Previously, a dozen or so LPTs have been detected within our Milky Way galaxy, but their source remained a puzzle. Leading theories pointed to magnetars (slowly rotating neutron stars) or binary systems involving white dwarfs, but neither hypothesis had strong, direct evidence. While some LPT cases hinted at a connection to white dwarf binaries, the actual process of material transfer, known as accretion, hadn't been definitively observed.
An international team, led by the University of Sydney, used the Australian Square Kilometer Array Pathfinder (ASKAP) radio telescope to study a source named ASKAP J174508.9-505149. Their observations provided the most compelling evidence to date linking LPTs to this specific type of binary system. "For the first time we have pinpointed the origin of these signals," explained Kovi Rose, a doctoral student at the University of Sydney, in a press release. "We’ve been able to show that the source for one of these transients comes from a white dwarf actively pulling material from a companion star."
Spectroscopic analysis revealed that ASKAP J1745-5051 exhibits specific hydrogen and helium emission lines, characteristic of "magnetic cataclysmic variables"—binary systems where a white dwarf pulls matter from a companion. Crucially, the orbital period of this binary system was found to be approximately 1.368 hours, almost perfectly matching the observed radio pulse repetition period of 1.345 hours. This suggests the companion star is an M6-class red dwarf, and the two stars orbit each other extremely closely, completing a revolution in just over an hour.
The research also shed light on how radio waves and X-rays are generated within these systems. While accretion heats gas, causing X-ray emissions, the powerful radio bursts appear to originate from the interaction of the stars' magnetic fields. The fact that the peaks of radio and X-ray emissions don't perfectly align suggests they are produced in slightly different locations. Data from China's Einstein Probe satellite also revealed X-ray emissions with a period of about 1.32 hours, consistent with the orbital motion.
Scientists consider ASKAP J1745-5051 a vital "Rosetta Stone" for understanding LPTs. "Some similar objects had been linked to binary systems before, but this is the first one where we can clearly see both stars and the accretion process in action," stated Tara Murphy, head of the Department of Physics at the University of Sydney. This discovery opens doors to studying extreme physics in star systems that can't be replicated on Earth, with researchers planning further observations across multiple wavelengths to unravel the mechanism behind LPT generation.
