University of Sydney team identifies source of mysterious repeating radio signals
Research led by the University of Sydney and CSIRO uses ASKAP telescope to solve decades-old astrophysics puzzle, linking cosmic radio bursts to magnetic cataclysmic variables.
An international research team led by the University of Sydney has identified the source of a mysterious repeating radio signal designated ASKAP J174508.9-505149. Using the Australian Square Kilometre Array Pathfinder (ASKAP) telescope, researchers determined the signal originates from a binary system consisting of a white dwarf and a red dwarf. The white dwarf is actively accreting material from its companion, generating periodic radio bursts and X-ray emissions. This discovery provides the strongest evidence to date linking long-period radio transients to magnetic cataclysmic variables, offering a potential key to understanding similar cosmic phenomena.
The object, designated ASKAP J1745-5051, was identified through a sky survey conducted by the ASKAP radio telescope. Spectroscopic observations confirmed hydrogen and helium emission lines, with the strong helium line indicating the system is a magnetic cataclysmic variable. These are close binary systems where a white dwarf accretes matter from a companion star, often guided by strong magnetic fields. The companion star was estimated to have a mass of 0.096 solar masses and a radius of 0.13 solar masses, classifying it as an M6-class red dwarf.
The orbital period of the binary system was calculated at approximately 1.368 hours, closely matching the radio pulse repetition period of 1.345 hours. This correlation confirms that the radio bursts are generated by the interaction of the two stars' magnetic fields as they orbit each other. The white dwarf, a dense remnant roughly the size of Earth but with the mass of the Sun, pulls material from the less dense red dwarf, creating the conditions for these periodic emissions.
Supporting data from the Einstein Probe satellite revealed X-ray emissions with a period of approximately 1.32 hours. The large amplitude fluctuations in these X-rays suggest that the accretion rate onto the white dwarf is changing over time. This marks the first time the regularity of X-ray emission in a long-period radio transient has been confirmed to stem from the orbital motion of a binary system. The radio pulses themselves are elliptically polarised and exhibit a "beat" pattern in frequency fluctuation, potentially due to misalignment between the white dwarf’s rotation and orbital motion.
Researchers regard this discovery as a crucial reference point for deciphering other long-period radio transients. Kovi Rose, a doctoral student at the University of Sydney’s School of Physics and CSIRO, stated that the team has pinpointed the origin of these signals, showing the source comes from a white dwarf actively pulling material from a companion star. Tara Murphy, head of the Department of Physics at the University of Sydney, noted that while similar objects had been linked to binary systems before, this is the first instance where both stars and the accretion process are clearly visible. The team plans to continue observations across radio, optical, and X-ray wavelengths to further elucidate the generation mechanism of these cosmic signals.
