Astronomers at Curtin University in Western Australia have linked mysterious radio pulses to an unusual stellar pairing involving a dead star that spins once every eight minutes and a companion similar to the Sun. The discovery, made by researchers at the university's node of the International Centre for Radio Astronomy Research (ICRAR), offers new clues about the origins of these cosmic signals.
Named GPM J071507−114153, the system comprises a white dwarf — the dense core left behind when a star dies — and a G-type star similar to the Sun. It is the first time radio pulses have been detected from a white dwarf orbiting a Sun-like star. Such signals have typically been observed in systems containing smaller and cooler red dwarf stars.
The system belongs to a class of objects called long-period transients (LPTs), which produce radio signals that switch on and off over periods ranging from minutes to hours. Around a dozen have been discovered since the first was identified by the ICRAR team in 2021.
“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 Dr Sam McSweeney, a commissioning scientist with the Square Kilometre Array Observatory.
The radio pulses also enabled researchers to detect stellar flares on the Sun-like star, similar to those that produce aurorae 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,” said Associate Professor Natasha Hurley-Walker, co-author of the study.
The team first identified the system in a survey using the Murchison Widefield Array in Western Australia before determining its precise position with the MeerKAT radio telescope in South Africa. Optical observations from the W M Keck Observatory in Hawaii confirmed its association with a G-type star. More than 100 hours of radio data were processed at the Pawsey Supercomputing Research Centre to validate the white dwarf's orbital motion.
“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,” McSweeney said.
