Unmasking Long-Period Radio Transients: Evidence Points to White Dwarfs

Long-period radio transients, cosmic radio pulses repeating every few minutes or hours, have puzzled astronomers since their discovery in 2022. These enigmatic objects exhibit periods ranging from 18 minutes to over six hours. Traditional understanding of neutron stars, which produce rapid radio pulses (pulsars), suggests they should not be able to generate radio waves while spinning at such slow rates.

A new study published in Nature Astronomy presents compelling evidence suggesting that these long-period transients are not neutron stars but rather white dwarf stars in binary systems with stellar companions, specifically M-type dwarfs.

White Dwarf Pulsars

White dwarfs are stellar remnants, much like neutron stars, but no isolated white dwarf has ever been observed to emit radio pulses. However, white dwarfs paired with M-type dwarfs in close binary systems can indeed produce radio pulses, known as white dwarf pulsars, with the first confirmed in 2016.

The identification of two long-period transients as white dwarf–M-dwarf binaries in 2025 spurred astronomers to question if long-period transients could be slower variations of established white dwarf pulsars.

GPM J1839-10: A Key Example

The study focused extensively on GPM J1839-10, a long-period transient discovered in 2023 with a 21-minute period. Its pulses have been detected in archival data dating back to 1988, making it uniquely long-lived among its kind.

Observations utilizing the Australian SKA Pathfinder (ASKAP), the MeerKAT radio telescope, and the Karl G. Jansky Very Large Array revealed a consistent and intricate pattern: pulses arrive in groups of four or five, with these groups subsequently appearing in pairs separated by two hours. The entire, complex pattern then repeats every nine hours.

This stable, nine-hour repetition strongly implies the signal originates from a binary system where two bodies orbit each other.

The derived masses from this orbital period are remarkably consistent with a white dwarf–M-dwarf binary.

Modelling the Phenomenon

A sophisticated model, building on a previous study of a white dwarf pulsar, suggests that GPM J1839-10 generates a radio beam as its magnetic pole sweeps through its companion's stellar wind. The varying alignment of the binary bodies with Earth's line-of-sight throughout their orbit accurately predicts the observed pulse pattern.

This model allowed for the detailed reconstruction of the system's geometry, including stellar separation and individual masses. GPM J1839-10 may therefore serve as a critical link between long-period transients and white dwarf pulsars, significantly advancing the understanding of these puzzling celestial objects.