An international team of astronomers led by Dr Iris de Ruiter , now at the University of Sydney, has shown that a white dwarf and a red dwarf star orbiting each other every two hours are emitting radio pulses.
Thanks to follow-up observations using optical and x-ray telescopes, the researchers were able to determine the origin of these pulses with certainty. The findings explain the source of such radio emissions found across the Milky Way galaxy for the first time.
The results are published in Nature Astronomy .
In recent years, better analysis techniques have given researchers the ability to detect 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 as to their source. This study led by Dr de Ruiter while at the University of Amsterdam changes this.
Dr de Ruiter, who received her doctorate from the University of Amsterdam in October 2024, is now a postdoctoral researcher at the University of Sydney. During the last year of her PhD, she developed a method to search for radio pulses of seconds to minutes in the historical archive of LOFAR , the Low-Frequency Array telescope in the Netherlands.
While improving the method, Dr de Ruiter 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 6.5m Multiple Mirror Telescope in Arizona and the Hobby-Eberly Telescope in Texas (USA) 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 centre of gravity every 125 minutes. They are located about 1600 light-years from us in the direction of the Big Dipper, also known as the Plough, within the Ursa Major constellation.
Astronomers believe that the radio emission is caused by the interaction of the red dwarf with the white dwarf's magnetic field.
Astronomers plan to study the ultraviolet emission of these entwined stars 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," Dr de Ruiter said. "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".
Neutron star monopoly broken
Because of this discovery, astronomers now know that neutron stars do not have the monopoly on bright radio pulses. In recent years, about 10 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 through the LOFAR data to find more such long-period pulses. Co-author Dr Kaustubh Rajwade (University of Oxford, UK) said: "There are probably many more of these types of radio pulses hidden in the LOFAR archive, and each discovery teaches us something new."
