Scientists at the Curtin University node of the International Centre for Radio Astronomy Research (ICRAR) have linked mysterious radio pulses to an unusual pairing of stars — a dead star that spins every eight minutes and a star similar to our own Sun.

The newly discovered system, known as GPM J071507−114153, consists of two stars orbiting each other: a white dwarf — the dense core left behind when a star dies — and a G-type star similar to our own Sun.

It is the first time radio pulses have been detected from a white dwarf orbiting a Sun-like star. Typically, such pulses are observed in systems with smaller and cooler red dwarf stars, meaning the discovery breaks new ground.

These types of stellar pairs belong to a broader class of objects known as long-period transients (LPTs), producing radio signals that switch on and off over intervals ranging from minutes to hours. Around a dozen have been detected since the first was discovered by the same ICRAR team in 2021, and astronomers are still working to understand them.

While several previously discovered LPT systems contain a white dwarf and another star, it has remained unclear which of the two stars was generating the radio pulses.

“This is the first time the pulses are clear enough to see the white dwarf moving in its orbit around its companion, so we know that the pulsations are coming from a region close to the white dwarf, or possibly even from the white dwarf itself,” said lead author and commissioning scientist with the Square Kilometre Array Observatory, Dr Sam McSweeney, who made this discovery while working as a researcher at the Curtin University node of ICRAR.  The team processed more than 100 hours of radio data at the Pawsey Supercomputing Research Centre to validate and understand the white dwarf motion.

Associate Professor Natasha Hurley-Walker, co-author on the paper, said that the pulses emitted by the white dwarf allowed the team to detect stellar flares on the Sun-like star, similar to those that create aurorae here on Earth.

“As a bonus, we also saw the white dwarf moving behind a region with a strong magnetic field, most likely a ‘stellar prominence’, which is a large loop of plasma erupting from a star’s surface.”

“It’s amazing that by using radio wavelengths we can detect the storms on a star over 5000 light-years away.”

ICRAR researchers have been at the forefront of discovering these rare systems.

“We detected this system in a large survey using the MWA (Murchison Widefield Array) to scan the entire Milky Way visible from Australia. We then used the MeerKAT radio telescope in South Africa to determine its precise position,” said Associate Professor Hurley-Walker.

After the LPT was located using the radio telescopes, the W.M. Keck Observatory on Maunakea, Hawaiʻi Island, confirmed its association with a G-type star through optical observations.

Both the MWA, led by Curtin University at Inyarrimanha Ilgari Bundara, the CSIRO Murchison Radio-Astronomy Observatory on Wajarri Yamaji Country in Western Australia, and MeerKAT, built and operated by the South African Radio Astronomy Observatory in the country’s North Cape province, serve as precursors for the SKA telescopes, SKA-Low in Australia and the SKA-Mid in South Africa, respectively.

Dr McSweeney said, “If we are already making such discoveries with precursor telescopes, just imagine how many more star systems we will be able to find, and what a beautifully detailed view of their signals we will have, once the SKAO telescopes are completely built.”

This study, ‘A long-period transient with a Sun-like companion’, was published in Nature Astronomy.