White Dwarf Pulsar Orbits Sunlike Star in Radio First

A dead star is flashing like clockwork beside a star that looks like the Sun. In research published in Nature Astronomy, Samuel J. McSweeney and colleagues report a long-period radio transient pulsing every 7.9 minutes, and they trace it to a white dwarf in orbit around a G-type star almost the same mass and temperature as our own sun. It's the first white dwarf pulsar found around a sunlike star, and it breaks the pattern the small family of these objects had set.

Long-period radio transients have puzzled astronomers since the first one appeared in 2022. They emit bright flashes of radio waves every few minutes to every few hours, far slower than an ordinary pulsar should manage. One early idea — an extremely slow-spinning neutron star — doesn't survive the theory, because a neutron star turning that slowly shouldn't produce radio waves at all. The answer had to be a different kind of system.

The sources identified so far pointed one way: a binary pairing a white dwarf, the remnant of a sunlike star, with a small, dim, cool red dwarf. Across the handful of transients whose source stars can be identified, that white dwarf and red dwarf combination kept repeating. The new system keeps the white dwarf and swaps the companion for something much brighter.

The detection came in late 2024, when the team was hunting new transients with the Murchison Widefield Array radio telescope in Western Australia. Using a search method developed by doctoral student Csanád Horváth, they spotted short flashes arriving every 7.9 minutes. Then the flashes stopped for weeks, and the team nearly gave up. Plotting every detection and nondetection together exposed the rhythm underneath: the pulses appear only in a window of about six hours, followed by 26 hours of silence. That's a binary signature — two stars orbiting once every 32 hours, with the pulses visible only when the pair lines up the right way.

Pinpointing the source took two more telescopes. The MeerKAT telescope in South Africa narrowed it to a tiny patch of sky holding a single faint star, and the Keck telescope in Hawaii recorded that star's spectrum, the fingerprint of its light. The result surprised the team. The companion wasn't a tiny red dwarf. It was a G-type star, the Sun's own class.

The pulsing partner's identity comes from timing and wobble. As it swings around its orbit, its pulses arrive up to 4 seconds early or late, which measures the orbit's size. The sunlike star's spectrum shows it barely wobbles under its partner's pull, so the partner must be much lighter than it. Combining the orbit's size, its 32-hour period and the spectrum puts the pulsing object at about two-thirds the Sun's mass — too light for a neutron star, and right for a white dwarf.

The likely history is violent. The team thinks the star that became the white dwarf first swelled into a giant and engulfed its companion, which spiraled inward, shrank the orbit, and survived while the giant's outer layers were ejected. Systems like this are probably common, but a faint white dwarf beside a bright star is hidden by glare in ordinary light. Radio pulses cut through it. If more transients are hiding white dwarfs around bright stars — some of them possible ancestors of Type Ia supernovae, the standard candles used to measure the universe — then radio surveys, and the coming SKA Observatory telescopes, could uncover a population that optical and X-ray instruments have been missing.