Astronomers trace radio pulses to dead star orbiting a Sun-like star

Astronomers have traced repeating radio pulses to a dead star spinning once every eight minutes as it orbits a Sun-like companion more than 5,000 light-years from Earth, according to research published in Nature Astronomy.

The stellar system, designated GPM J071507−114153, pairs a white dwarf — the dense, burnt-out core left when a star exhausts its nuclear fuel and sheds its outer layers — with a G-type star in the same broad category as the Sun. It is the first time such radio pulses have been detected from a white dwarf orbiting a Sun-like star; previously identified systems of this kind featured smaller, cooler red-dwarf companions.

The discovery was made by researchers at the Curtin University branch of the International Centre for Radio Astronomy Research (ICRAR). The system belongs to a class of objects called long-period transients (LPTs), which emit radio waves that brighten and fade over periods ranging from several minutes to hours. Their origins remain poorly understood. The same ICRAR team found the first known example in 2021, and only about a dozen have been identified since.

Pinpointing the source

For the first time, the researchers obtained radio observations detailed enough to follow the white dwarf as it moved along its orbit, letting them narrow down where the pulses originate. They analyzed more than 100 hours of radio observations using computing resources at the Pawsey Supercomputing Research Centre.

"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, now a commissioning scientist with the Square Kilometre Array Observatory, who made the discovery while at Curtin University's ICRAR branch.

The radio data also gave astronomers an unexpected window onto the companion star, revealing large magnetic storms on its surface. The researchers said the unusual pairing raises new questions about the role of binary interactions and magnetic fields in producing these signals, and could help explain the origins of some of the Milky Way's most puzzling radio emissions.

Only a handful of LPTs have been studied in detail, so the team said further monitoring will be needed to determine whether white-dwarf-plus-Sun-like-star systems are rare or simply hard to detect.