A small, dense dead star caught tearing material from a companion star has helped astronomers solve one of the universe’s most perplexing mysteries and researchers at UNC-Chapel Hill played a key role in uncovering the answer.
Working as part of an international collaboration, Carolina astronomers Dr. Igor Andreoni, Dr. Brad Barlow and doctoral student Jonathan Carney helped identify the source of a mysterious class of cosmic signals known as long-period radio transients. The findings, published in Nature Astronomy , provide some of the strongest evidence yet for the origin of these unusual bursts of radio waves, which can repeat over periods ranging from minutes to hours and have puzzled astronomers since their discovery.
The breakthrough began when researchers led by graduate student Kovi Rose at the University of Sydney used the Australian Square Kilometre Array Pathfinder (ASKAP) radio telescope to detect powerful bursts of radio waves repeating every 1.4 hours. The observations with multiple telescopes suggested the signals were coming from a binary star system containing a white dwarf, a dense stellar remnant roughly the size of Earth but with a mass comparable to the Sun, and a low-mass red dwarf companion.
To test the idea, the Carolina team quickly secured observing time on the 4.1-meter Southern Astrophysical Research (SOAR) Telescope in Chile.
“The SOAR observations were essential to the success of this project,” said Andreoni, assistant professor in the department of physics and astronomy at UNC-Chapel Hill. “Our data revealed that we were looking at two stars orbiting each other and we could measure the rotation period.”
Late-night observations conducted by Andreoni, Barlow and Carney revealed telltale signatures in the system’s light that confirmed the presence of a magnetic cataclysmic variable — a binary system in which a white dwarf pulls material from a companion star. As that material spirals toward the white dwarf, it heats to extreme temperatures, producing distinctive optical and X-ray emissions.
“The atmosphere in the observing room that night was electric,” said Barlow, associate professor in the department of physics and astronomy at UNC-Chapel Hill. “As soon as the spectrum came up on the screen, those unmistakable emission lines told us we had something special on our hands. It’s not often you get to play a role in discoveries of this magnitude.”
The system, designated ASKAP J1745−5051, consists of a white dwarf and a red dwarf star with about one-tenth the Sun’s mass. The stars orbit each other so closely that they complete a full orbit in just over an hour. While material is stripped from the red dwarf and collected onto the white dwarf, interactions between the stars’ powerful magnetic fields generate regular radio bursts that can be detected across vast distances in space.
“The resolution and sensitivity of the SOAR telescope instrumentation were key,” said Carney, a graduate student in the department of physics and astronomy at UNC-Chapel Hill. "The observations were made possible in part by the Goodman spectrograph, a Carolina-designed instrument mounted on the SOAR Telescope in Chile. UNC originally initiated the SOAR Telescope project in 1987 to expand access to the southern sky for students and researchers."
The discovery may finally explain the origin of some long-period radio transients. When astronomers first detected these signals, many suspected they came from unusually slow-spinning neutron stars known as pulsars. Existing theories suggest neutron stars rotating this slowly should not be capable of producing such emissions. The new findings strengthen an alternative explanation: that some of these mysterious signals are generated by interacting binary star systems involving white dwarfs.
Researchers say ASKAP J1745−5051 could serve as a crucial guide for interpreting future discoveries. Much like the Rosetta Stone helped scholars decipher ancient Egyptian hieroglyphics, this system may provide astronomers with a reference point for determining whether newly discovered long-period radio transients originate from pulsars, white dwarf binaries or other exotic objects.
Beyond solving a longstanding astronomical puzzle, the system offers scientists a rare opportunity to study extreme magnetic fields, high-energy plasma and the behavior of matter under conditions that cannot be reproduced in laboratories.
The study is available online in the journal Nature Astronomy at: https://www.nature.com/articles/s41550-026-02882-x
Nature Astronomy
Periodic radio and X-ray emission from an accreting white dwarf binary
1-Jun-2026