First Sun-like Star Hosts White Dwarf Pulsar, Revealing New Source for Long-Period Radio Transients

Author: The Conversation

The Conversation reports the first Sun-like star in a binary with a white dwarf that powers long-period radio transients. A distant radio signal detected with the Murchison Widefield Array was followed up with MeerKAT and Keck observations, pinpointing a Sun-like (G-type) companion. Timing of pulses shows the system is a binary with a 32-hour period, and the companion is heavy enough to rule out a neutron star, consistent with a white dwarf pulsar. This discovery expands the known sources of intermittent radio bursts and suggests radio surveys can uncover hidden white-dwarf binaries missed by optical and X-ray surveys. The finding has implications for the evolution of binary stars and the progenitors of Type Ia supernovae.

• Pulses repeat every 7.9 minutes but only during a six-hour window in a 32-hour orbit
• Star is Sun-like; the compact object is too light to be a neutron star
• First known white-dwarf pulsar in orbit around a Sun-like star
• Radio surveys may reveal hidden white-dwarf binaries missed by other wavelengths

Overview

The article details a breakthrough in understanding long-period radio transients, a class of cosmic radio flashes that recur from time to time. After 2022’s initial discoveries, researchers traced several signals to binary systems involving a white dwarf and a dim companion. In a Nature Astronomy study published today, researchers report the first long-period transient powered by a white dwarf in orbit around a Sun-like star. The work combines radio observations with precision optical spectroscopy to characterize the system and establish its unusual nature.

The discovery story

In late 2024, a search for new long-period transients was conducted with the Murchison Widefield Array (MWA) in Western Australia. Using a technique developed by PhD student Csanád Horváth, the team detected short, clockwork-like radio pulses with a cadence of 7.9 minutes. After a period of silence, the detections resumed, and when all detections and non-detections were plotted together, a pattern emerged: the pulses appeared only within a roughly six-hour window, followed by a 26-hour gap. The natural interpretation is a binary star system where two stars orbit each other roughly once every 32 hours, and the radio pulses are visible only when the geometry aligns so that the emission is directed toward Earth.

The MeerKAT telescope in South Africa localized the source to a tiny patch of sky containing a faint star. The Keck telescope in Hawai‘i then captured the star’s spectrum, revealing a G-type star with a mass and temperature similar to the Sun. This was a surprise because some long-period transients previously linked to red dwarfs in orbit around white dwarfs were thought to be typical; this object, however, is a Sun-like star, broadening the types of stars that can host these intermittent radio signals.

Weighing a star we can’t see

One of the key puzzles was the nature of the pulsing companion. The team used timing to infer the orbit's size: as the pulsing object moves around its companion, the radio pulses arrive slightly earlier or later than expected, up to about four seconds, due to the extra travel time when the source is farther away in its orbit. The Sun-like star’s spectrum shows only a tiny wobble, implying the star is much heavier than its companion. Combining orbital size, period, and the spectrum data, the researchers deduced the pulsing object has a mass about two-thirds that of the Sun. A neutron star, which would be far more massive, is ruled out. The conclusion: the pulsing object is a white dwarf, making this the first confirmed white-dwarf pulsar in orbit around a Sun-like star.

What strange systems are hiding in the dark?

The discovery suggests that white dwarfs next to bright, sun-like stars may be common but hard to detect with traditional optical or X-ray surveys due to glare. Radio pulses cut through the glare, enabling a new way to uncover these systems. Long-period transients may thus be a Rosetta Stone for identifying previously hidden white-dwarf binaries, potentially shedding light on the population of systems that could become Type Ia supernovae as the white dwarf accretes matter or merges with a companion. The study also underscores the importance of next-generation radio facilities and the SKA Observatory, which are expected to reveal many more such systems across different stellar types and environments.

Formation and implications

How did a Sun-like star end up with a white-dwarf companion? The proposed scenario involves the progenitor star of the white dwarf expanding into a giant, engulfing its companion, which then spirals inward while the outer layers are ejected. The glare of the bright, Sun-like star has historically masked the faint white dwarf, but the radio pulses offer a clean, penetrating probe. If long-period transients around bright stars are shown to host white-dwarf companions, this would imply a hidden population of binary systems that could be precursors to Type Ia supernovae. Type Ia supernovae serve as standard candles for distance measurements in cosmology, so uncovering more of these systems could refine our understanding of cosmic expansion. The authors anticipate that future radio arrays, including SKA, will enable systematic searches and provide deeper insight into the lives and deaths of Sun-like stars across our galaxy and beyond.

Looking ahead

This discovery opens a new window into stellar evolution and binary dynamics, highlighting radio astronomy's potential to reveal systems optical and X-ray observations miss. As radio telescope sensitivity and coverage improve, more long-period transients are likely to be identified, potentially unveiling a broader population of white-dwarf binaries in diverse stellar environments. The findings pave the way for a more complete census of white-dwarf binaries and their roles in stellar evolution, explosion mechanisms, and the cosmic distance ladder. The Nature Astronomy study emphasizes that multi-wavelength follow-up—radio timing, optical spectroscopy, and astrometric/radial velocity analyses—will remain essential for fully characterizing these exotic systems.

Conclusion

By identifying a white-dwarf pulsar in a Sun-like star system, the study expands our understanding of long-period radio transients and reveals a new, hitherto hidden population of white-dwarf binaries. The results have broad implications for binary-star evolution, Type Ia supernova progenitors, and our methods for surveying the cosmos, underscoring the continued importance of radio astronomy and next-generation facilities in unveiling the universe’s hidden corners.