For a decade, a radio signal has puzzled astronomers. Every two hours, a pulse from the constellation Ursa Major travels through space. Its astonishing regularity and unusual duration defy classic explanations. What is the source of these enigmatic emissions?
These pulses, detected by the LOFAR radio telescope, differ from known fast radio bursts (FRBs). They last several seconds and repeat with astonishing regularity. Thanks to complementary observations, researchers have identified the source: a binary system where the magnetic fields of the two stars interact violently.
Artist's illustration of a red dwarf (left) and a white dwarf (center) orbiting each other. Their orbit is so tight that their magnetic fields interact, generating radio pulses every two hours.
Image by Daniëlle Futselaar/artsource.nl. A binary system with intense magnetic interactions
The system, named ILT J1101, consists of a white dwarf and a red dwarf in a tight orbit. Their complete revolution takes 125.5 minutes. At each pass, their magnetic fields collide, producing a radio pulse detectable from Earth.
Optical observations confirmed the presence of the two stars. Variations in the motion of the red dwarf, measured by spectroscopy, revealed the presence of its invisible companion: the white dwarf. The latter, too faint to be seen directly, was identified by its gravitational influence.
This discovery is a first. Until now, only neutron stars were known to emit long radio pulses. This binary system shows that other compact objects, such as white dwarfs, can produce similar signals.
A cosmic enigma with major implications
The radio pulses from ILT J1101 raise new questions. Are they produced by the white dwarf's magnetic field alone, or by the interaction of the two stars? Researchers are working on these hypotheses while exploring other similar systems.
This discovery could shed light on the origin of some FRBs, those fast radio bursts still poorly understood. It shows that binary systems, with dead stars, can generate powerful and regular radio emissions. Astronomers hope to find other examples to better understand these phenomena.
The next steps include studying the system's ultraviolet emissions, which could reveal the temperature of the white dwarf and its history. Each new observation provides valuable clues to solving this cosmic enigma.
Article author: Cédric DEPOND