Researchers identify a mystifying Long-Period Transient with 100% polarized radio emission, suggesting new type of cosmic radio source. A team of astronomers at ASTRON, the Netherlands Institute for Radio Astronomy, has discovered a mysterious new cosmic radio source that challenges current theories about how dead stars can produce such powerful emissions. Using the LOFAR (Low Frequency Array) radio telescope, the team picked up the unusual signal as part of a study led by astronomer Sanne Bloot. This research was published today in the scientific journal Astronomy & Astrophysics.
Published by the editorial team, 17 July 2025
Discovery of a new class of cosmic radio emitters
The source, officially named ILT J163430+445010, appears to belong to a previously unknown class of objects known as long-period transients (LPTs): enigmatic celestial
bodies that emit bright radio pulses far more slowly than typical pulsars.
Located thousands of light-years from Earth, this system produces radio pulses every 14 minutes, exhibiting an extraordinary property. Some pulses have radio waves that spin in circles (circular polarization), while others vibrate in straight lines (linear polarization).
“J1634+44 is unique, even among the small population of long-period transients that have been found so far,” said Sanne Bloot. “Its rapid polarisation switching, from circular to linear, has never been observed before on any type of object and provides us with a rare opportunity to study the physics behind these bright and perplexing pulses.”
To identify the nature of the object emitting the pulses, the researchers combined radio observations with observations in infrared, optical, and ultraviolet. Their analysis points to a white dwarf: the hot, dense core left behind when a star like our Sun dies. This white dwarf has a surface temperature between 15,000 and 33,000 degrees Celsius, which is much hotter than our Sun.
Evidence for a hidden companion triggering radio emission
Another extraordinary property of the objects is that the radio pulses arrive in a curious rhythm: they come in pairs, but only after the dead star has spun around several times without producing any detectable signals. Astronomers believe this pattern indicates that the white dwarf has a companion object, possibly another dead star or a failed star, known as a brown dwarf, which triggers the radio emissions through magnetic interactions.
“What is remarkable is that the time between pulse pairs seems to follow a choreographed pattern,” said Dr Harish Vedantham, astronomer at ASTRON and co-author of the study. “We think the pattern holds crucial information about how the companion triggers the white dwarf to emit radio waves. Continued monitoring should help us decode this behaviour, but for now, we have a real mystery on our hands.”
Only ten of these slow-pulsing radio sources have been found so far, making each new discovery precious for understanding how they work. Unlike most previous discoveries, which were hidden behind clouds of dust and stars, this one sits in a relatively clear part of the sky and can be studied in detail.
The discovery was possible thanks to a systematic search for pulses in data from the LOFAR Two Metre Sky Survey, highly sensitive survey of the northern sky. As LOFAR continues its sky survey, the team expects to discover several more such objects. These forthcoming discoveries could conclusively explain how dead stars spring back to life as radio-emitting beacons.
J1634+44 was simultaneously discovered with the CHIME telescope, by a team led by Dr. Fengqui Adam Dong. Their paper, titled “CHIME/FRB Discovery of an Unusual Circularly Polarized Long-Period Radio Transient with an Accelerating Spin Period”, has appeared in the Astrophysical Journal Letters.
LOFAR reveals rare pulsating dead stars
The source emerged from a systematic search for unusual radio signals in the LOFAR Two-Metre Sky Survey, which monitors large areas of the northern sky. LOFAR’s sensitivity to circularly polarised radio waves, those that spin like corkscrews, enabled the team to detect this system’s distinctive signature. Over nearly four years, the astronomers tracked the source, recording 19 separate radio bursts. The brightest of these was hundreds of times stronger than the faintest detectable signal.
This discovery demonstrates how modern radio telescopes can reveal rare cosmic phenomena previously invisible to astronomers. As LOFAR continues its sky survey, the team expects to discover several more of these mysterious, radio-emitting dead star systems, which could reveal an entirely new population of cosmic objects. This research and the expected forthcoming discoveries could conclusively explain how dead stars can spring back to life as radio-emitting beacons.
Research team
The research is published in Astronomy & Astrophysics, and is the result of a collaboration between ASTRON, the University of Groningen, the University of Amsterdam, the University of Texas at Austin, the University of Hawaii, Leiden University, and the University of Edinburgh.
📽️ In this short video, lead researcher Sanne Bloot explains more about the research: https://youtube.com/shorts/i8Re1gUxntg?si=3lvh1htB0n_Vidco