Strange radio pulses that baffled astronomers have been traced to their point of origin, a white dwarf and red dwarf binary pair, solving a cosmic radio mystery.
Follow-up optical and X-ray telescope observations confirm that this is the first time astronomers have found the source of such a radio emission in the Milky Way galaxy. Dr Iris de Ruiter, now at the University of Sydney but working from the University of Amsterdam during the project, led the research, with participation from an international team of astronomers based in the UK and Netherlands.
Long Period Transients
The long bursts, lasting from seconds to minutes, are called long-period transients (LPTs) and are emitted with pauses of minutes or even hours. Advances in analysis techniques in recent years brought the local Milky Way radio bursts to astronomers’ attention, remaining mysterious as theorists debate their possible trigger. By determining the burst source for the first time, Dr. de Ruiter has identified a starting point for answers.
The pulses vary significantly from the Fast Radio Bursts, a hot astronomy topic over the last decade. Those millisecond-long bursts occur every few seconds and are emitted from neutron stars called pulsars.
Hunting the Radio Pulse Source
In her work, Dr. de Ruiter devised a novel method to pick out radio pulses in the Low-Frequency Array telescope’s (LOFAR) historical archive. In 2022, she discovered a pulse in data initially collected in 2015, followed by six more, as she honed her discovery technique. The mysterious pulses were arriving from a binary source dubbed ILTJ1101.
Now knowing where to look, researchers performed follow-up observations with two US-based telescopes: the 6.5m Multiple Mirror Telescope in Arizona and the Hobby-Eberly Telescope in Texas (USA). Astronomers found not one but two stars spinning around a center of gravity in just over two hours. The red dwarf and white dwarf are 1600 light years away, nestled in the Ursa Major constellation.
“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”.
Viewing the Origin
With a source identified, some astronomers hypothesize that the red dwarf interacting with the white dwarf’s magnetic field generates radio bursts. Another possibility is that the white dwarf’s magnetic field produces the pulse on its own. Further observations will allow researchers to identify the mechanism more conclusively.
Astronomers plan to investigate further by thoroughly studying the source’s ultraviolet emissions. They project that the investigation will reveal crucial information about the white dwarfs’ temperature and the histories of both stars.
One of the most interesting components of the discovery is how it reframes existing research on radio bursts, previously only seen emitting from neutron stars. Researchers have discovered ten similar radio emitting systems but have yet to identify whether the signals originate with neutron or white dwarf stars.
Next Step in Radio Pulse Research
“This finding is very exciting! We are starting to find a few of these LPTs in our radio data,” said co-author Dr. Kaustubh Rajwade of Oxford University. “Each discovery is telling us something new about the extreme astrophysical objects that can create the radio emission we see. For instance, the unexpected observation of coherent radio emission from the white dwarf in this study could help probe the evolution of magnetic fields in this type of star.”
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Dr. Rajwade now leads researchers searching the LOFAR data to find more long-period pulses.
“There are probably many more of these types of radio pulses hidden in the LOFAR archive, and each discovery teaches us something new,” said co-author Dr. Rajwade. “Thanks to this discovery, we now know that compact objects other than neutron stars are capable of producing bright radio emission.”
The paper “A White Dwarf Binary Showing Sporadic Radio Pulses at the Orbital Period” appeared on March 12, 2025, in Nature Astronomy.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted atryan@thedebrief.org, and follow him on Twitter@mdntwvlf.