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White dwarf and red dwarf duo emit radio pulses every two hours

An international team of astronomers led by scientists from the Netherlands has shown that a white dwarf and a red dwarf orbiting each other every two hours are emitting radio pulses. Thanks to observations with several telescopes, the researchers were able to determine the origin of these pulses with certainty for the first time. Their results are in Nature Astronomy.

In recent years, thanks to better analysis techniques, researchers have detected radio pulses that last from seconds to minutes and seem to come from stars in the Milky Way. There have been many hypotheses about what triggers these pulses, but until now there has been no hard evidence. An international study led by Iris de Ruiter of the Netherlands changes this.

De Ruiter, who received her Ph.D. from the University of Amsterdam in October 2024, is now a postdoctoral researcher at the University of Sydney (Australia). During the last year of her Ph.D., she developed a method to search for radio pulses of seconds to minutes in the LOFAR archive. While improving the method, she discovered a single pulse in the 2015 observations. When she subsequently sifted through more archive data from the same patch of sky, she discovered six more pulses. All the pulses came from a source called ILTJ1101.

Red and white dwarf

Follow-up observations with the 6.5 m Multiple Mirror Telescope in Arizona and the Hobby-Eberly Telescope in Texas (U.S.) showed that it is not one flashing star, but two stars that together cause the pulse. The two stars, a red dwarf and a white dwarf, orbit a common center of gravity every 125 minutes. They are located about 1,600 light-years from Earth in the direction of the Big Dipper.

Astronomers believe that the radio emission is caused by the interaction of the red dwarf with the white dwarf's magnetic field.

In the future, astronomers plan to study the ultraviolet emission of ILTJ1101 in detail. This will help to determine the temperature of the white dwarf and learn more about the history of white and red dwarfs.

"It was especially cool to add new pieces to the puzzle," says de Ruiter. "We worked with experts from all kinds of astronomical disciplines. With different techniques and observations, we got a little closer to the solution step by step."

Monopoly broken

Thanks to this discovery, astronomers now know that neutron stars do not have the monopoly on bright radio pulses. In recent years, about ten such radio-emitting systems have been discovered by other research groups. However, these groups have not yet been able to prove whether these pulses come from a white dwarf or a neutron star.

Researchers are now searching all the LOFAR data to find more such long-period pulses. Co-author Kaustubh Rajwade (University of Oxford, UK) observes, "There are probably many more of these types of radio pulses hidden in the LOFAR archive, and each discovery teaches us something new."