A new discovery by astronomers at the University of Sydney, published in Nature Astronomy, has finally revealed the origin of a rare and puzzling class of cosmic signals known as long-period radio transients. Using CSIRO’s ASKAP radio telescope, researchers have identified a unique binary star system that could redefine how scientists understand extreme stellar physics.
A Rare Binary System Unlocks Cosmic Mysteries
The newly identified system, ASKAP J1745−5051, consists of a white dwarf, a dense stellar remnant roughly the size of Earth but with the mass close to the sun, paired with a red dwarf star about one-tenth the sun’s mass. Orbiting each other in just over an hour, the two stars engage in a dramatic gravitational dance. Material from the smaller star is drawn toward the white dwarf, heating as it spirals in and producing bursts of radio waves and X-rays.
“For the first time we have pinpointed the origin of these signals, confirming the source to be a ‘cataclysmic variable,’ or an accreting white dwarf star,” said Ph.D. student Kovi Rose, lead author. “Long-period radio transients have puzzled astronomers for years. We’ve only found about a dozen, and their origins have been unclear. Now, 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.”
The system’s emissions occur at regular intervals linked to the orbital motion. Yet the radio and X-ray peaks are offset, indicating they originate from different regions within the system. “These emissions are all tied to the orbital motion of the system,” Mr. Rose said. “But interestingly, the radio and X-ray signals don’t peak at the same time, which tells us they’re being produced in different regions of the system.”
Solving A Cosmic Puzzle With Multi-Wavelength Observations
Previously, long-period radio transients were suspected to originate from slow-spinning neutron stars, known as pulsars. Models predicted such stars could not produce these signals, leaving astronomers searching for alternative explanations. ASKAP J1745−5051 now provides direct evidence that binary systems involving white dwarfs are responsible for at least some of these enigmatic bursts.
“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,” said Professor Murphy, Head of School at the University of Sydney and Chief Investigator at OzGrav.
The system also emits regular X-rays, making it only the second long-period radio transient known to do so and the first where the origin of this regularity has been confirmed.
The combination of ASKAP’s sensitivity, resolution, and sky coverage made this detection possible, capturing signals that would otherwise go unnoticed. Researchers describe ASKAP J1745−5051 as a stellar Rosetta Stone, offering a template to decode other long-period radio transients.
“This system gives us a way to decode these signals. 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,” Mr. Rose said.
A Laboratory for Extreme Physics
Beyond unraveling cosmic signals, ASKAP J1745−5051 offers a natural laboratory to explore extreme plasma physics, magnetism, and gravity. Observations of matter under intense gravitational forces and strong magnetic fields reveal processes impossible to replicate on Earth.
“These systems are natural laboratories,” said Mr. Rose. “They allow us to test our understanding of how matter behaves in strong magnetic fields and under intense gravitational forces.” The discovery highlights the potential of such rare binary systems to advance not only radio astronomy but also our fundamental knowledge of astrophysical phenomena.
Expanding the Map of Cosmic Transients
The international team plans further observations using a combination of radio, optical, and X-ray telescopes to explore how these bursts are generated and whether similar mechanisms explain the broader population of long-period radio transients.
“Each new discovery is helping us piece together the bigger picture,” Mr. Rose said. “We’re only just beginning to understand this new class of cosmic events.” With global collaboration spanning Australia, the United States, China, Canada, Spain, and Israel, the discovery, detailed in Nature Astronomy, marks a major milestone in the quest to decode the universe’s most elusive signals.