Astronomers have traced mysterious radio signals to an unusual pair of stars more than 5,000 light-years from Earth. One is a dead star that rotates every eight minutes, while its companion closely resembles our own Sun.
The discovery was made by researchers at the Curtin University branch of the International Centre for Radio Astronomy Research (ICRAR). Their findings reveal a previously unseen combination of stars producing radio pulses and offer new clues about the origins of some of the Milky Way’s most puzzling signals.
The stellar system, designated GPM J071507−114153, contains a white dwarf and a G-type star orbiting one another. A white dwarf is the extremely dense remnant of a star that has exhausted its nuclear fuel and shed its outer layers. Its companion belongs to the same general category of stars as the Sun.
Until now, astronomers had detected similar radio pulses in systems containing white dwarfs and smaller, cooler stars known as red dwarfs. This marks the first time such signals have been identified in a system where a white dwarf orbits a Sun-like star.
A Rare Star System With Mysterious Radio Pulses
The newly identified pair belongs to an unusual group of astronomical objects called long-period transients (LPTs). These objects produce radio emissions that appear and disappear over periods lasting anywhere from several minutes to hours.
Despite growing interest in these strange signals, their origins remain poorly understood. The same ICRAR research team discovered the first known example in 2021, and only about a dozen have been identified since then.
Some of these systems contain a white dwarf alongside another star, but astronomers have struggled to determine which member of the pair is responsible for the radio emissions.
The latest discovery provides an important breakthrough. For the first time, researchers have obtained radio observations detailed enough to follow a white dwarf as it travels around its stellar companion. This allows them to pinpoint the likely location of the radio pulses much more accurately.
“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.
McSweeney, now a commissioning scientist with the Square Kilometre Array Observatory, made the discovery while working at Curtin University’s ICRAR branch.
To confirm the findings and examine the white dwarf’s orbital motion, the researchers analyzed more than 100 hours of radio observations using computing resources at the Pawsey Supercomputing Research Centre.
Giant Magnetic Storms Detected 5,000 Light-Years Away
The radio signals revealed more than the movement of the dead star. They also gave astronomers a surprising opportunity to investigate magnetic activity on its Sun-like companion.
According to study co-author Associate Professor Natasha Hurley-Walker, the observations exposed stellar flares associated with powerful magnetic disturbances. Similar magnetic processes on our own Sun can lead to auroras on Earth when energetic particles interact with our planet’s magnetic field and atmosphere.
The team also detected evidence that the white dwarf passed behind an especially magnetically active region near its companion.
“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.”
A stellar prominence consists of electrically charged gas held in enormous loops by magnetic fields. These structures can extend far above a star’s surface, providing clues about the powerful forces shaping its outer atmosphere.
The ability to detect such activity across thousands of light-years demonstrates how much information astronomers can extract from radio signals, even when the stars themselves are extraordinarily distant.
“It’s amazing that by using radio wavelengths we can detect the storms on a star over 5000 light-years away.”
Powerful Radio Telescopes Reveal a Hidden Stellar Pair
ICRAR researchers have played a leading role in identifying long-period transients, and the latest discovery relied on observations from several major astronomical facilities around the world.
The system was initially detected during a sweeping radio survey of the Milky Way conducted with the MWA (Murchison Widefield Array) in Western Australia.
“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 radio telescopes narrowed down the system’s location, astronomers turned to the W.M. Keck Observatory on Maunakea, Hawaiʻi Island. Optical observations confirmed that the radio source was associated with a G-type star, establishing the presence of a companion similar to the Sun.
The MWA, led by Curtin University, operates at Inyarrimanha Ilgari Bundara, the CSIRO Murchison Radio-Astronomy Observatory on Wajarri Yamaji Country in Western Australia.
The MeerKAT telescope was built and is operated by the South African Radio Astronomy Observatory in South Africa’s North Cape province.
Both instruments are precursors to the next generation of Square Kilometre Array telescopes. The Australian facility, SKA-Low, and the South African facility, SKA-Mid, are being developed to provide much greater sensitivity and detail when observing the radio universe.
For astronomers studying rare stellar systems, these future capabilities could dramatically expand the number of objects they can discover and reveal much more about the processes responsible for their unusual signals.
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.”
The findings were published in Nature Astronomy in a study titled “A long-period transient with a Sun-like companion.”