An international team of astronomers led by Dr Iris de Ruiter has shown that a white dwarf and a red dwarf star orbiting each other every two hours are emitting radio bursts.
Thanks to follow-up observations using optical and x-ray telescopes, the researchers were able to determine the origin of the radio bursts with certainty.
The findings explain the source of such radio emissions found across the Milky Way galaxy for the first time.
What triggers radio bursts?
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 of their source.
This study, led by Dr de Ruiter while at the University of Amsterdam, changed this.
During the last year of her PhD, she developed a method to search for radio bursts 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, which all came from a source called ILTJ1101.
Discovering red and white dwarf stars
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 radio pulses.
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.
Dr de Ruiter said: “It was especially cool to add new pieces to the puzzle. 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.”
Breaking the neutron star monopoly
Due to this discovery, astronomers now know that neutron stars do not have a monopoly on bright radio bursts.
In recent years, other research groups have discovered about ten such radio-emitting systems. 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, from the University of Oxford, concluded: “There are probably many more of these types of radio pulses hidden in the LOFAR archive, and each discovery teaches us something new.”
