A stellar “Rosetta stone” reveals the source of mysterious cosmic signals

Astronomers have traced a mysterious type of repeating cosmic signal to an unusual pair of stars, providing the strongest evidence yet for the source of one of astronomy's most puzzling phenomena.

The discovery was made by an international research team led by scientists at the University of Sydney using CSIRO's ASKAP radio telescope. Their findings identify the origin of a rare class of objects known as long-period radio transients, mysterious bursts of radio waves that have puzzled astronomers since they were first detected in only a handful of locations across the Milky Way.

Lead author Kovi Rose, a PhD student in the University of Sydney's School of Physics and CSIRO, said the team was finally able to connect one of these enigmatic signals to a specific type of stellar system.

"For the first time we have pinpointed the origin of these signals, confirming the source to be a 'cataclysmic variable', or an accreting white dwarf star," said Mr. Rose.

"Long-period radio transients have puzzled astronomers for years," Mr. Rose said. "We've only found about a dozen, and their origins have been unclear. Now, we've been able to show that the source for one of these transients comes from a white dwarf actively pulling material from a companion star."

The newly identified system, known as ASKAP J1745−5051, consists of a white dwarf and a red dwarf locked in an extremely close orbit. A white dwarf is the dense remnant of a dead star, roughly the size of Earth but with a mass comparable to that of the Sun. Its companion is a much larger but less dense red dwarf star containing about one-tenth the Sun's mass.

As the white dwarf pulls gas from its companion, the material heats up and emits X-rays. At the same time, interactions between the stars' magnetic fields generate powerful radio bursts. Together, these emissions repeat on a regular cycle every 1.4 hours.

"These emissions are all tied to the orbital motion of the system," Mr. Rose said. "But interestingly, the radio and X-ray signals don't peak at the same time, which tells us they're being produced in different regions of the system."

The researchers found that the radio waves are likely produced where the stars' magnetic fields collide and interact with the stream of charged material flowing toward the white dwarf. This process creates tightly focused bursts of radiation that sweep through space.

When long-period radio transients were first discovered, many astronomers suspected they might be unusually slow-spinning neutron stars known as pulsars. However, existing models suggest neutron stars rotat