An international team led by astronomers at the University of Sydney has found the clearest evidence yet for the source of an unusual class of cosmic signals. They identified a rare stellar system that serves as a natural laboratory for studying extreme physics.
Using CSIRO’s ASKAP radio telescope, researchers detected a small dense white dwarf stripping material from its larger but less dense red dwarf companion. As the material spirals inward, it generates repeating bursts of radio waves and X-rays every 1.4 hours. The results appear in Nature Astronomy.
Lead author and Ph.D. student Kovi Rose said the discovery provides the first confirmed identification of long-period radio transients, signals previously detected in only a few areas of the galaxy. The source is a cataclysmic variable, an accreting white dwarf star. These transients have puzzled astronomers, with only about a dozen known and unclear origins. The new data show one originates from a white dwarf drawing material from a companion.
The system, called ASKAP J1745-5051, pairs a white dwarf roughly Earth-sized but near solar mass with a red dwarf of about one-tenth solar mass. The stars orbit each other in just over an hour. Material drawn to the white dwarf heats and emits X-rays while magnetic field interactions produce regular radio bursts. The emissions link to orbital motion, though radio and X-ray peaks occur at different times, indicating separate production regions.
Long-period radio transients were once thought to be slow-spinning neutron stars, or pulsars. Current models indicate such slowly rotating neutron stars should not produce these signals. The discovery supports the idea that at least some bursts arise from binary systems involving white dwarfs. The system is only the second known long-period radio transient to emit regular X-rays, and the first with a confirmed cause for the regularity.
The system was found with the ASKAP telescope at the CSIRO Murchison Radio-astronomy Observatory. Its combination of coverage, resolution and sensitivity enabled detection of the unusual signals. Researchers suggest ASKAP J1745-5051 could serve as a reference for understanding other long-period radio transients and help determine whether they resemble pulsars or binary systems.
