China detects rare radio signal from distant star system

Chinese researchers analyzing 2021 observations from the Five-hundred-metre Aperture Spherical Radio Telescope (FAST) detected a radio signal designated NBS 260108 that appeared to come from the K2-155 star system, approximately 238 light-years from Earth, according to WION and BGNES. The signal exhibited characteristics that scientists associate with artificial transmitters: an exceptionally narrow frequency range, a gradual frequency shift to lower frequencies, and detection in only one of the telescope's 19 beams — the one aimed at K2-155. The star system hosts three super-Earth planets, including K2-155d, which is nearly 1.6 times Earth's size, orbits every 40.7 days, and lies near the habitable zone where liquid water could exist. "This system's habitable-zone super-Earth made it an intriguing SETI [the Search for Extraterrestrial Intelligence] target," the authors wrote in their study published in The Astronomical Journal, as reported by WION.

However, further analysis complicated the initial excitement. BGNES reported that researchers identified similar radio signals during observations of three other stars, strengthening the possibility that the source was terrestrial radio interference or equipment belonging to the telescope itself. The team plans to examine additional recordings from all 19 beams to establish the signal's origin. WION noted the researchers acknowledged that "further improvements in technology are needed to verify whether this mysterious signal actually came from deep space, or was it a false alarm caused by human-made interference on Earth." For now, the observation has not been accepted as confirmed evidence of extraterrestrial technology.

Separately, a different discovery was published in Nature on the same day: a long-period radio transient named GPM J071507−114153 with a 7.9-minute period, identified as a binary system comprising a low-mass white dwarf and a G-type star similar to the Sun. This system, found using the Murchison Widefield Array, shows radio pulses modulated by a 1.3-day orbital period. The Nature paper concludes that in such white dwarf binaries, coherent radio emission depends on interaction with the companion star, which can be a G-type star in day-long orbits. This discovery is distinct from the FAST detection at K2-155.