Radio pulses reveal a white dwarf binary system more than 5,000 light-years away

The radio flashes lasted only a few seconds. During an active stretch, they came roughly eight minutes apart. But the most revealing part of the signal was a small shift in when each pulse reached Earth. The flashes ran early or late in a pattern that followed the motion of their source around another star.

The system, GPM J071507−114153, pairs a white dwarf with a star similar to the Sun. It is the first known example of this kind of repeating radio source with a Sun-like companion. Previously identified white dwarf binaries in this class have tended to feature smaller, cooler companions.

Sam McSweeney led the work while at the Curtin University node of the International Centre for Radio Astronomy Research. He is now with the Square Kilometre Array Observatory. The team reported its findings in Nature Astronomy.

A white dwarf is the dense remnant left after a Sun-like star exhausts its fuel and sheds its outer layers. Astronomers have found some white dwarfs in close pairs with red dwarf companions. The new system gives them a chance to see how a different kind of companion might affect the signals.

The Murchison Widefield Array detected the source during a survey of the Milky Way. It recorded 214 pulses between December 2024 and September 2025. MeerKAT, in South Africa, detected another 33 in a follow-up campaign and narrowed down their position. Optical spectra from the W. M. Keck Observatory showed that a star at that location was a G-type star with an estimated mass close to the Sun’s.

The shorter clock ran at about 7.9 minutes. The team interprets that period as the white dwarf’s spin. But the radio pulses did not appear every time the clock predicted one. Including observations that found nothing helped reveal a second rhythm. Detections clustered within an activity window of about six hours that recurred every 32.47 hours, roughly the time the two stars take to orbit each other.

The companion’s light was important because the radio data alone could tell the team only where the pulses appeared and how they behaved. The optical spectra gave the astronomers a way to identify the other star and estimate its temperature at about 5,500 kelvins.

The two rhythms describe different motions. The compact star spins many times during one orbit. The orbit changes how the stars are arranged along our line of sight. In other close binaries, orbital geometry also shapes what astronomers can see. Here it gives the team a way to ask whether the pulses depend on how the stars face Earth or interact with one another.

As the emitting region moves closer to Earth in its orbit, the radio waves have slightly less distance to travel. Half an orbit later, they have farther to go. That difference can make pulses arrive ahead of or behind a prediction based on the average interval. The flashes were brief enough for the researchers to track those deviations. They processed more than 100 hours of radio data at the Pawsey Supercomputing Research Centre.

Astronomers call this a light travel time delay. A change in distance of one light-second changes the arrival time by one second. By comparing pulses at similar points across several orbits, the team could look for a timing pattern that repeated even though individual flashes differed in brightness.

The optical data gave the team a second constraint. The researchers looked for changes in the companion’s spectral lines that would reveal its motion toward and away from Earth. The spectra placed an upper limit on that motion at the observed phase. Combined with the radio timing, it strongly favored a white dwarf over a neutron star if the emission region is close to the compact object.

The timing traces the motion of the emitting region. It cannot tell astronomers whether the radio waves originate at the white dwarf’s surface or in its immediate magnetic surroundings.

Other repeating bursts offer comparisons for testing which conditions produce the signals. Some interacting stars exchange material, but the new study leaves the mechanism in this system open.

The radio waves carried information beyond their arrival times. Some were polarized, meaning their electric fields had a preferred orientation or pattern of rotation. As radio waves travel through magnetized plasma, their polarization can rotate by different amounts at different frequencies. Astronomers can use that effect, called Faraday rotation, to investigate material along the path.

MeerKAT recorded changes in that rotation as the stars moved around one another. Some of the largest shifts came near the end of the active window, when the white dwarf was approaching a position behind its companion as seen from Earth. The pattern is consistent with pulses passing through the companion’s corona, the outer region of its atmosphere. Long-running observations of the Sun offer a nearby example of how stellar magnetism changes over time.

That measurement is especially useful at this distance. The team does not need to see a loop of plasma directly to test whether magnetized material affected the signal. The changing orbit naturally sends the pulses along different paths through the space around the companion.

A prominence, a loop of plasma held by a magnetic field, is one possible explanation for part of the signal. Ejected plasma could also affect what the radio waves encounter. As in studies that compare distant eruptions with solar activity, the resemblance helps researchers interpret the measurements while leaving room for other explanations.

Long-period transients can send detectable radio pulses minutes or hours apart. Several have turned out to contain a compact star paired with a cooler companion. Finding a Sun-like star in this system expands the range of binaries astronomers can compare. It also gives them another way to test ideas about the role of magnetic fields in white dwarf systems.

The next observations could refine the masses and orbit and test whether the changes in polarization recur at the same points on successive orbits. A repeatable change would help map the companion’s magnetic surroundings. Changes from one orbit to the next could point to activity that comes and goes, as happens in stellar eruptions.

The same pulses can serve both purposes. Their arrival times trace the motion of the source, while their polarization records what the waves pass through. Following both over more orbits may help explain how the system generates the flashes and what those flashes reveal about a star more than 5,000 light-years away.

Link between long-period transients and white dwarf pulsars
Researchers use binary motion to test a connection between two classes of pulsing sources. (Nature Astronomy, February 2026)

A long-period radio transient active for three decades
Archived observations show that another repeating source stayed active for decades. (Nature, July 2023)

A 5.3-min-period pulsing white dwarf in a binary detected from radio to X-rays
Observations across several wavelengths reveal a different rapidly spinning white dwarf in a binary. (Nature Astronomy, June 2023)

A radio transient with unusually slow periodic emission
The discovery paper describes a source that emitted bright pulses roughly every 18 minutes. (Nature, January 2022)

A radio-pulsing white dwarf binary star
The authors report pulsed radiation from AR Scorpii, an important comparison for newer discoveries. (Nature, July 2016)

Research findings are available online in the journal Nature Astronomy.

The original story "Radio pulses reveal a white dwarf binary system more than 5,000 light-years away" is published in The Brighter Side of News.

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