Scientists trace eight-minute radio pulses to rare white dwarf star system

Astronomers at Australia’s Curtin University and the International Centre for Radio Astronomy Research have linked mysterious radio pulses to an unusual pairing of stars, the institutions announced. The pulses come from a system called GPM J071507−114153, located more than 5,000 light-years from Earth.

The system consists of two stars orbiting each other: a white dwarf, described as the dense core left behind when a star dies, and a G-type star similar to the Sun. The white dwarf spins every eight minutes.

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.

“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 Dr Sam McSweeney, lead author and commissioning scientist with the Square Kilometre Array Observatory, who made the 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.

These types of stellar pairs belong to a broader class of objects known as long-period transients, 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 long-period transient systems contain a white dwarf and another star, it had remained unclear which of the two stars was generating the radio pulses.

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,” Hurley-Walker said.

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

The researchers detected the system in a large survey using the Murchison Widefield Array to scan the entire Milky Way visible from Australia. They then used the MeerKAT radio telescope in South Africa to determine its precise position. After the long-period transient 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 Murchison Widefield Array, 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.

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