Dead star spinning every eight minutes found orbiting a Sun-like star

Astronomers in Western Australia have traced mysterious radio pulses to a dead star that spins once every eight minutes while orbiting a star much like the Sun, more than 5,000 light-years from Earth.

The system, designated GPM J071507-114153, consists of a low-mass white dwarf — the dense core left behind when a star exhausts its fuel and sheds its outer layers — and a G-type star of the same general category as the Sun. It is the first time such radio pulses have been detected from a white dwarf orbiting a Sun-like star; earlier examples were mostly paired 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) and published in the journal Nature Astronomy.

A rare class of blinking objects

The pair belongs to the rare class known as long-period transients (LPTs), which switch their radio emission on and off over periods ranging from minutes to hours. The same ICRAR team identified the first known example in 2021, and only about a dozen have been found since.

Until now it was unclear which star in such pairs produced the pulses. The new observations are detailed enough to show the white dwarf moving along its orbit, placing the source close to it — or on it.

"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, an astronomer at ICRAR and a commissioning scientist with the Square Kilometre Array Observatory.

McSweeney and colleagues processed more than 100 hours of radio data using computing resources at the Pawsey Supercomputing Research Centre to confirm the star's motion.

Storms on a distant twin of the Sun

The data yielded a bonus: stellar flares on the Sun-like companion, similar to those that create aurorae on Earth, and the white dwarf passing behind what is most likely a stellar prominence — a huge loop of plasma erupting from the star's surface.

"The pulses emitted by the white dwarf allowed our team to detect stellar flares on the Sun-like star, similar to those that create aurorae here on Earth," said Dr Natasha Hurley-Walker of ICRAR. "It's amazing that by using radio wavelengths we can detect the storms on a star over 5,000 light-years away."

The team said the finding offers fresh clues to the origins of long-period transients, whose emission mechanisms remain poorly understood.