A cosmic ray from a magnetar? Scientists have a new theory for the mysterious ‘Wow!’ signal

Nearly 50 years after a radio telescope in rural Ohio picked up the famous “Wow!” signal, astronomers may be closing in on a natural explanation — though they’re careful to stress it remains unconfirmed. Researchers revisiting decades-old archival data have proposed that the signal may have been produced when a cold hydrogen cloud briefly flared after being struck by an intense burst of radiation from an object such as a magnetar or soft gamma repeater.

The original detection occurred for just 72 seconds on the night of August 15, 1977, arriving from the direction of the constellation Sagittarius, close to the 1,420 MHz hydrogen line — a frequency long considered one of the most likely channels an intelligent civilisation might use to communicate across interstellar distances. Astronomer Jerry Ehman circled the sequence “6EQUJ5” on the printout days later and wrote “Wow!” in the margin, giving the signal its enduring name.

What made the detection so remarkable was how closely it matched what researchers with the Search for Extraterrestrial Intelligence (SETI) expected a distant artificial transmission might look like: it gradually increased and decreased in intensity as a fixed celestial source would, occupied an extremely narrow frequency unlike most natural cosmic emissions, and lasted the telescope’s full 72-second observing window before vanishing. It has never been detected again despite decades of follow-up observations, including a targeted search by the Breakthrough Listen initiative using the Green Bank Telescope and Allen Telescope Array, which found no convincing technosignature.

While the magnetar hypothesis offers a plausible astrophysical explanation, researchers emphasise it remains one possibility among several, alongside human-made interference, instrumental errors, and the enduring, unconfirmed possibility of an extraterrestrial transmission.