Since 2022, astronomers have been tracking a class of objects known as long‑period radio transients—sources that flash bright radio waves at intervals ranging from a few minutes to several hours. Early investigations linked many of these transients to binary systems consisting of a cool red dwarf and a white dwarf, the dense remnant of a star similar to the Sun.
Discovery of an unusual repeating signal
In late 2024, a team using the Murchison Widefield Array (MWA) in Western Australia applied a search technique devised by PhD student Csanád Horváth. The method uncovered a series of short radio bursts that arrived with clockwork regularity every 7.9 minutes. After a brief period of activity the bursts ceased, and weeks passed without detections. By plotting both detections and non‑detections, researchers recognized a pattern: the pulses were visible for roughly six hours before disappearing for about 26 hours.
The six‑hour on‑window and 26‑hour off‑window suggested a binary system whose orbital period is 32 hours. In such a configuration the radio emission would be observable only when the two objects line up in a geometry that allows the signal to reach Earth.
Pinpointing a Sun‑like companion
Follow‑up observations with the MeerKAT telescope in South Africa narrowed the source to a tiny region of sky containing a single faint star. The team then turned to the Keck telescope in Hawai‘i to obtain a spectroscopic “fingerprint” of the star. Contrary to expectations, the spectrum revealed a G‑type star—essentially a star with a mass and temperature comparable to the Sun—rather than a diminutive red dwarf.
Timing analysis of the radio pulses showed that their arrival times shifted by up to four seconds as the pulsing object moved through its orbit. These variations indicate the size of the orbit and, combined with the orbital period, allow a calculation of the masses involved. The Sun‑like star displayed only a slight wobble, implying it is substantially more massive than its unseen partner. The derived mass of the pulsing object is about two‑thirds that of the Sun, a value too low for a neutron star, which would typically be around 1.4 solar masses.
Given its mass and the nature of the radio emission, the researchers conclude that the companion is a white dwarf acting as a pulsar—the first such white‑dwarf pulsar identified in orbit around a Sun‑like star.
Implications for stellar evolution and supernovae
The formation scenario proposed by the authors involves the progenitor of the white dwarf expanding into a giant phase, engulfing its companion, and spiralling inward. The subsequent ejection of the giant’s outer layers would leave a compact white dwarf tightly bound to the surviving Sun‑like star.
White‑dwarf binaries are of particular interest because some are thought to evolve into Type Ia supernovae, the stellar explosions used as “standard candles” for measuring cosmic distances and the expansion rate of the universe. Detecting such binaries via their radio pulses could reveal a population that optical and X‑ray surveys miss, owing to the glare of the bright companion star.
The authors anticipate that next‑generation radio facilities, such as the Square Kilometre Array (SKA) Observatory, will uncover many more long‑period transients. Expanding the sample to include a variety of host stars will deepen understanding of the life cycles of Sun‑like stars and the pathways that lead to Type Ia supernovae.
Steve Lopez is a Senior Editorial Columnist and Health & Public Policy reporter for News Raise. Steve focuses on healthcare advancements, medical technologies, and public health policies.
