The Star That Ate Its Neighbor and Solved a 57-Year Cosmic Mystery
When Jocelyn Bell Burnell detected the first pulsar in 1967, her first instinct was that she had found signals from an alien civilization. She and her thesis advisor Antony Hewish seriously considered the LGM hypothesis — Little Green Men. Within months, the explanation arrived: a rotating neutron star, a remnant of supernova death, generating lighthouse-like radio beams across the cosmos. The universe's capacity for misdirection had once again defeated the alien hypothesis.
Now astronomers have repeated that pattern.
An international team led by PhD candidate Kovi Rose at the University of Sydney has identified the source of a puzzling class of repeating cosmic radio signals that astronomers have debated for 57 years — since the pulsar discovery opened this chapter of cosmic misidentification. Their discovery, published in Nature Astronomy, traces the signals to ASKAP J1745-5051 — a white dwarf star locked in a close orbital dance with its smaller red dwarf companion, stripped of material that generates radio waves and X-rays as it spirals inward. Every 1.37 hours, the system coughs up a burst of radiation that sweeps through space like a lighthouse beam.
The finding settles a years-long debate about what produces long-period radio transients, a rare class of objects first identified only in recent decades. Astronomers had proposed two main candidates: slowly spinning neutron stars, or white dwarf binaries in close orbits. Rose's team used CSIRO's ASKAP radio telescope in Australia and the MeerKAT array in South Africa to localize the signal, then obtained optical spectra from the SOAR and Magellan telescopes in Chile. The spectra showed the characteristic signature of a magnetic cataclysmic variable: strong hydrogen and helium emission lines that only appear when a white dwarf is actively pulling material from a neighbor, according to SpaceAustralia.
"For the first time we have pinpointed the origin of these signals, confirming the source to be a cataclysmic variable," Rose said.
The team found that radio and X-ray signals from the system peak at different phases of the orbit, suggesting they originate in distinct physical regions. The X-ray emission comes from material heating up as it falls toward the white dwarf. The radio bursts appear to come from where the two stars' magnetic fields collide and interact with the incoming stream of charged particles, per the Nature Astronomy paper.
The system is only the second known long-period radio transient to produce regular X-rays, and the first where astronomers have confirmed the exact mechanism driving the periodicity. Of the roughly dozen known long-period radio transients in the Milky Way, none had been spectroscopically linked to a specific stellar type until now.
"This system gives us a way to decode these signals," Rose said. "It could help us determine whether other long-period transients are more like pulsars or like white dwarf systems, acting like a stellar Rosetta stone."
The discovery has practical implications beyond solving a puzzle. ASKAP J1745-5051 becomes a reference object: a confirmed white dwarf binary emitting predictable radio and X-ray bursts at a known period. Astronomers can now use it to calibrate observations of the remaining transients in the known population, and potentially to search archival data from previous surveys for missed detections. The Square Kilometre Array, currently under construction in South Africa and Australia, is expected to dramatically increase the rate of new detections — giving researchers many more candidates to test against this template.
Not every long-period radio transient is likely to share this origin. Some may still prove to be ultra-long-period magnetars, neutron stars with extraordinarily strong magnetic fields rotating far more slowly than ordinary pulsars. But Rose's result tips the balance: at least some of these signals come from a place much closer to ordinary stellar physics than the magnetar hypothesis implies.
"These systems are natural laboratories," Rose said. "They allow us to test our understanding of how matter behaves in strong magnetic fields and under intense gravitational forces that we cannot recreate on Earth."
The team plans to continue monitoring the system across radio, optical, and X-ray wavelengths. Each new observation tightens the model and brings the next unknown transient closer to identification.