Somewhere in our galaxy, at a distance beyond 5,000 light-years, something is switching on like a lighthouse every 7.9 minutes. Researchers at ICRAR, a radio astronomy institute in Western Australia, now know what it is: a burnt-out white dwarf circling together with a G-type star, the same class as the Sun.
The pair, catalogued as GPM J071507−114153, is the first case in which radio pulses of this kind have been tied to a white dwarf whose partner resembles the Sun. Until now, comparable signals had been linked to pairs involving dim red dwarfs, which are less massive than the Sun.
The flashes do not arrive all the time. They are visible for roughly six hours, then vanish for more than a day. The team’s explanation is geometry: the two stars circle each other about every 32 hours, and only when they line up suitably does the beam sweep across Earth. Each flash corresponds to one rotation of the compact dead star, which turns roughly every eight minutes.
These objects belong to a puzzling family called long-period transients, with roughly twelve examples catalogued since 2021. A lingering question has been which star in such pairs produces the signal. In this case the signal was clean enough for the team to follow the compact star as it travelled around its partner. According to lead author Sam McSweeney, that places the origin of the flashes near the white dwarf, “or possibly even” on the dead star itself.
The system turned up in a sky survey with the Murchison Widefield Array, and South Africa’s MeerKAT telescope pinned down its location. The team spent well over a hundred hours of telescope recordings checking that orbital wobble, using computers at the Pawsey centre.
There was an unexpected bonus. As the beam passes through the companion’s atmosphere, it revealed flares and probably a giant loop of plasma on that star. Co-author Natasha Hurley-Walker called it “amazing” that such stellar storms can be studied from so far away. Details of the discovery are laid out in a paper for the journal Nature Astronomy.
