The ‘Wow! signal’ has finally been deciphered
Back in the 1970s, a concentrated effort in the search for extraterrestrial intelligence (SETI) was well underway at the Big Ear radio telescope in Delaware, USA. More formally known as the Ohio State University Radio Observatory, this unusual telescope looked more like a sports arena than a conventional steerable dish. Nevertheless, between 1965 and 1971, it produced the most complete map of the radio sky yet attempted.
In the aftermath of that success, the telescope was devoted to SETI observations, which it carried out from 1973 until it was decommissioned in 1995. Just once during that period, on 15 August 1977, it detected a signal that might have come from an alien transmitter. A few days later, astronomer Jerry Ehman was inspecting the telescope’s computer printout when he discovered the tell-tale registration of a huge burst of radio energy and wrote the word “Wow!” in the margin.
Decades of follow-up observations and analysis have failed to come up with a convincing explanation of the signal, with all known terrestrial and cosmic phenomena being ruled out … until now, due to our new knowledge of rare transient events such as flares on the highly magnetised neutron stars known as magnetars, which have only recently been studied.
In research recently announced, a team from the USA and Colombia have used data from a since decommissioned radio telescope at Arecibo in Puerto Rico to look for similar phenomena to the Wow! signal. And they’ve found them, differing only from the original in their lower intensity. All these signals carry the wavelength signature of cold hydrogen, the most abundant element in the universe. It’s commonly expected to be the preferred wavelength for communication by intelligent extraterrestrials – hence the Big Ear’s tuning to this wavelength in the original SETI experiment.
The team’s thinking is that clouds of cold hydrogen are occasionally excited by the passage of high-energy radiation from a flaring magnetar a long way behind them, and become much brighter as a result. This prosaic explanation of the Wow! signal could be tested by looking in the same direction for transient signals with the wavelength signature of much more distant objects. And finding them would be the clincher for the Wow! signal as a natural phenomenon.
