What was the Wow! signal?

The Wow! signal was a strong narrowband radio signal detected on August 15, 1977, by Ohio State University's Big Ear radio telescope, which was then being used in the search for extraterrestrial intelligence. It appeared to come from the direction of the constellation Sagittarius. It has never been detected again, and no explanation has been confirmed. [1]

No one noticed the signal at the time. A few days later, volunteer astronomer Jerry Ehman reviewed a line-printer record in which each line showed the radio energy in 50 frequency channels, averaged over 10 seconds. Intensity was coded in 31 steps, using the digits 0 to 9 and then the letters A to U. Ehman circled the sequence 6EQUJ5 and wrote "Wow!" beside it in red ink, which gave the event its name. According to the SETI Institute, the signal was picked up on only one of the 50 channels. [2] [3]

The string 6EQUJ5 is often mistaken for an encoded message. It is only the signal's intensity over time in the observatory's measuring system. [1]

Big Ear could only be adjusted for altitude and relied on Earth's rotation to sweep across the sky, so it observed any given point for 72 seconds. A steady source fixed on the sky would therefore rise for about 36 seconds, peak, and then fade. The Wow! signal showed this pattern, which suggested a celestial origin rather than local interference. Its bandwidth was under 10 kHz, and it was close to 1420 MHz, the frequency of neutral hydrogen. The signal appeared to be an unmodulated continuous wave, although modulation faster than 10 seconds or slower than 72 seconds would not have been detectable. [1]

Robert Dixon, who directed the observatory at the time, has argued that because the signal followed the telescope's beam shape it was at least as far away as the Moon, and that it turned off when the direction was observed again soon afterward. He took this to indicate an intelligent origin rather than a natural phenomenon. He also noted that later attempts with other telescopes failed to find it again. [2]

Others point to the lack of repetition as an argument against extraterrestrial life, and think a natural event that 1977 instruments could not analyze is more likely. In 2024 a team led by Méndez, from the Planetary Habitability Laboratory at the University of Puerto Rico at Arecibo, proposed that a powerful transient source, such as a magnetar flare, briefly brightened a cold hydrogen cloud through maser-like emission or superradiance. They based this on weaker, similar signals from neutral hydrogen clouds in Arecibo survey data. The SETI Institute describes this as a plausible natural explanation that does not definitively solve the mystery, since the one-off event is hard to confirm. Earlier ideas, such as reflections from space debris, interstellar scintillation and comet hydrogen clouds, were considered briefly, and none has been confirmed. [3] [4] [5] [1]

Sources agree that the cause is not settled. The natural hydrogen-cloud hypothesis is the explanation currently receiving the most attention in these sources, but the results do not say how widely specialists accept it. [2] [5]