Scientists say they have identified the source of a mysterious radio signal that flashes on and off every eight minutes.
Using a powerful radio telescope, researchers from Curtin University traced the precisely timed pulses to an unusual binary star system more than 10,000 light-years from Earth.
Known as GPM J071507-114153, the system contains a dead star called a white dwarf and a G-type star that closely resembles the Sun.
The object belongs to a rare group known as long-period transients, which produce powerful radio pulses at intervals ranging from minutes to hours.
Only around a dozen long-period transients have been identified since the class was first discovered in 2021, and astronomers are still working to determine how they form.
The latest finding is the first evidence of radio pulses coming from a white dwarf orbiting a Sun-like star.
Astronomers have previously detected pulsing radio signals in systems containing white dwarfs. However, they could not establish which of the two stars was producing the emissions.
Lead author Dr Sam McSweeney, a commissioning scientist with the Square Kilometre Array Observatory radio telescope, said: ‘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.’
Scientists have identified a strange star system that produces a radio signal every eight minutes (artist’s impression)
Curtin University researchers traced the regular pulses to an unusual stellar pairing located more than 10,000 light-years from Earth
Long-period transients rank among the most unusual phenomena detected by radio telescopes across the universe.
They appear as exceptionally powerful and tightly focused bursts of radio waves and X-rays, often originating in the distant reaches of space.
When these objects were first discovered, their precisely timed flashes led some people to wonder whether they could be signals sent by an extraterrestrial civilisation.
Astronomers now think the energy bursts are produced by the rapidly rotating remnants of dead stars.
Co-author Dr Natasha Hurley-Walker, an associate professor at the Curtin Institute of Radio Astronomy, told the Daily Mail: ‘Our best idea is that the white dwarf has a strong magnetic field, and its stellar companion is constantly feeding it charged particles through its stellar wind.
‘When those particles meet the white dwarf’s magnetosphere, they get accelerated and produce the pulses we see, a bit like the way the Sun’s wind interacts with Earth’s magnetic field to make aurorae.’
As the white dwarf spins, its beam sweeps across Earth in much the same way that a lighthouse beam crosses the surrounding darkness, creating the regular flashes detected by astronomers.
GPM J071507-114153 contains a white dwarf and a faint G-type star similar to the Sun, which cannot be seen with the naked eye (pictured)
The fastest long-period transient identified so far flashes every 421 seconds. The slowest produces a 30-second pulse once every 2.9 hours.
For the study, published in Nature Astronomy, the team used the Murchison Widefield Array radio telescope to survey the entire section of the Milky Way visible from Australia.
After detecting the tell-tale pulse from GPM J071507-114153, the researchers carried out further radio and visible-light observations. These allowed them to pinpoint the system and identify the type of stars involved.
The observations provided the first clear indication that the radio pulses were coming from a white dwarf—the dense core left behind when a star reaches the end of its life—or from the region immediately surrounding it, as it orbited a bright, Sun-like star.
The result was unexpected because radio pulsars, the best-known sources of repeating radio flashes, are generally neutron stars: the extraordinarily dense remnants of massive stars.
White dwarfs are far more common than neutron stars, but only a small number have been linked to radio pulses. Until now, no isolated white dwarf had been observed producing this kind of emission.
The system also contains another surprising feature.
‘The companion is a Sun-like star, which we didn’t think was possible, and the white dwarf is spinning once every 7.9 minutes, which is extraordinarily fast for something of its size,’ says Professor Hurley-Walker.
As the white dwarf spins and follows its orbit, a beam of radiation sweeps across Earth like a lighthouse, creating the appearance of a regular flash
‘The fact that we now see this happen with a Sun-like companion, not just a red dwarf, suggests that the only necessary ingredients are a white dwarf and a companion star in an orbit that delivers enough material to the white dwarf’s magnetic field.’
The researchers were also able to detect subtle evidence of activity on the surface of the companion star.
Professor Hurley-Walker says: ‘The pulses act like a flashlight shining through the atmosphere of the companion!
‘As the white dwarf swings round to the far side of its orbit, the radio waves have to travel through the star’s outer atmosphere, the corona, before they reach us.
‘Magnetic fields in that plasma twist the polarisation of the radio waves, and we see this signature change very rapidly as the orbit progresses.’
By tracking these changes, the team found signals they believe were caused by a ‘stellar prominence’—a vast loop of plasma erupting from the surface of the companion star.
Professor Hurley-Walker adds: ‘I find it amazing that we can study the weather on a star more than 10,000 light years away, something that’s otherwise impossible!’
