Dead star spinning every 8 minutes found pulsing beside a Sun-like star

Astronomers have traced mysterious radio pulses to an unusual pair of stars more than 5,000 light-years from Earth, where a dead star rotating every eight minutes orbits a companion that closely resembles the Sun.

The system, designated GPM J071507−114153, contains a white dwarf — the extremely dense core left behind when a star exhausts its nuclear fuel and sheds its outer layers — and a G-type star of 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 they had been seen only in systems pairing white dwarfs with smaller, cooler red dwarfs.

The discovery was made by researchers at the Curtin University node of the International Centre for Radio Astronomy Research (ICRAR) in Western Australia. Their findings were published in the journal Nature Astronomy.

A rare class of blinking objects

The pair belongs to a group of astronomical objects called long-period transients (LPTs), which emit radio signals that switch on and off over periods ranging from several minutes to hours. The ICRAR team identified the first known example in 2021, and only about a dozen have been found since. Their origins remain poorly understood.

Earlier systems contained a white dwarf alongside another star, but astronomers struggled to determine which member of the pair produced the radio emission. The new observations are the first detailed enough to track a white dwarf as it travels around its companion, allowing researchers to pin down the likely source of the pulses.

"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 working at Curtin University's ICRAR branch.

Magnetic storms on the companion

To confirm the finding and examine the dead star's orbital motion, the team analyzed more than 100 hours of radio observations using computing resources at the Pawsey Supercomputing Research Centre. The signals also gave astronomers a surprising window into magnetic activity on the companion star, revealing massive magnetic storms there.

The researchers said the combination of stars and pulses provides fresh clues to the origins of some of the Milky Way's most puzzling signals.