An unexplained radio signal detected in 1977 known as the Wow! signal, which some have interpreted as an alien message, may have been the result of a natural galactic laser-like beam.
On 15 August 1977, the Big Ear radio telescope at Ohio State University detected a brief, powerful burst of radio waves with an unusually narrow range of frequencies, similar to atomic hydrogen’s natural emission frequency. No known astronomical processes could have produced such an emission, and astronomer Jerry Ehman, who worked at the telescope, jotted down the phrase “Wow!” in red pen on a printout of the signal.
The now famous Wow! signal has defied explanation in the decades since its observation. Some people have said, in the absence of a more compelling explanation, that an advanced alien civilisation could have been responsible. Astronomers have also put forward less exotic ideas, such as fast-moving comets releasing clouds of hydrogen gas, but it was unclear how they might produce a strong enough signal.
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Now, at the University of Puerto Rico at Arecibo and his colleagues have spotted similar signals from clouds of hydrogen atoms in front of red dwarf stars in our galaxy. While they are less powerful than the original Wow! signal, Méndez and his team think that a powerful light source passing behind the clouds, like a flare from a highly magnetic neutron star – a magnetar – could stimulate the hydrogen atoms to fire out a beam of microwave radiation, known as a maser.
MĂ©ndez started looking for Wow!-like signals when he realised that the Arecibo telescope, which collapsed in 2020, and the Big Ear telescope had similar experimental set-ups. He and his team were already searching for signals from nearby red dwarf stars as a part of a project looking for habitable exoplanets, so they combed this data and found multiple examples that were remarkably similar in their frequency range to the Wow! signal.
“The signals that we detected from these clouds are less bright because they are not illuminated by a magnetar,” says Méndez. “When you do the calculation, they will become much, much brighter [if they were].”
While astronomers have spotted masers in space from hydrogen molecules – pairs of hydrogen atoms bonded together – they have never seen one from an atomic hydrogen cloud, which is what would be required to reproduce the Wow! signal, says Méndez.
Proving that that was what caused the signal would be an astrophysical discovery in itself, he says. It is possible that astronomers could go back and survey the original part of the sky to try to find a hydrogen cloud in front of a magnetar, but unless this object happened to be letting off a flare, which is a very rare event, then it would be difficult to spot, says MĂ©ndez.
It is an interesting idea, says at the University of Manchester, UK, but it is unclear whether atomic hydrogen masers can exist or whether they are required as an explanation instead of just the magnetar by itself. “A magnetar is going to produce [short] radio emissions as well. Do you really need this complicated maser stuff happening as well to explain the Wow! signal?” he asks. “Personally, I don’t think so. It just makes a complicated story even more complicated.”
arXiv
