Astronomers have identified an unusual binary star system whose radio signal turns on roughly every eight minutes, providing the clearest evidence yet that a white dwarf can power such pulses while orbiting a star similar to the Sun. The system, designated GPM J071507−114153, lies more than 5,000 light-years from Earth.
The pair consists of a white dwarf — the compact core left after a star exhausts its fuel — and a G-type companion. Researchers at the Curtin University node of the International Centre for Radio Astronomy Research say this is the first detection of radio pulses from a white dwarf paired with a Sun-like star. Previously identified systems of this kind have generally involved smaller, cooler red dwarfs.
GPM J071507−114153 belongs to a class called long-period transients. These objects emit radio signals separated by intervals ranging from minutes to hours, far slower than the rapid pulses associated with many familiar radio sources. About a dozen long-period transients have been detected since an ICRAR team reported the first in 2021, but astronomers are still determining the mechanisms that generate their emissions.
The new system helps narrow that question because its pulses were sufficiently clear for researchers to track the white dwarf's orbital motion. Lead author Sam McSweeney said the movement places the source of the pulsations close to the white dwarf and possibly on the object itself. The team processed more than 100 hours of radio observations at the Pawsey Supercomputing Research Centre to validate the motion.
The signal also gave the scientists a way to probe activity around the companion. As the white dwarf moved through its orbit, the observations indicated that it passed behind a strongly magnetized region that the researchers interpret as a stellar prominence — a large loop of plasma extending from the Sun-like star. The team says the radio pulses enabled it to detect flaring activity analogous to the solar events that can produce aurorae at Earth.
Researchers first found the source in a Milky Way survey conducted with the Murchison Widefield Array in Western Australia. Follow-up observations with South Africa's MeerKAT telescope refined its location. Optical work at the W. M. Keck Observatory in Hawaii then confirmed the association with a G-type star. The Murchison array and MeerKAT are precursor instruments for the Square Kilometre Array facilities planned in Australia and South Africa.
The study, titled “A long-period transient with a Sun-like companion,” was published in Nature Astronomy. Its result does not yet provide a complete explanation for every long-period transient, but it supplies a firm link between one repeating radio source and the white-dwarf region of a binary system.
That link gives astronomers a more specific target for models of how magnetic fields, orbital motion and stellar plasma produce slow repeating bursts. The researchers expect the Square Kilometre Array's greater sensitivity and detail to reveal more systems and allow closer comparisons among them.
