Mysterious ‘Wow!’ Radio Signal Might Finally Have an Explanation—and No, It’s Not Aliens

In 1977, astronomer Jerry Ehman was shocked to find that overnight, Ohio State University’s Big Ear radio telescope had picked up a strikingly intense and narrow radio transmission from space, which lasted at least 72 seconds. On the printed data report, Ehman famously circled the series of letters and numbers that represented the signal in bright red ink—and he scrawled a now-famous word in the margin.

“Without thinking, I wrote ‘Wow!’” Ehman told the Cleveland Plain Dealer’s Barry Kawa in 1994. “It was the most significant thing we had seen.”

The reason for his surprise was because the signal’s intensity and highly specific frequency—similar to that emitted naturally by hydrogen atoms—suggested the event wasn’t your typical radio emission from space, but rather an unnatural phenomenon. Perhaps unsurprisingly, many people began to suggest that the so-called “Wow! signal” was a message from extraterrestrials.

But now, three astronomers have proposed a new cause behind the infamous radio signal—and it isn’t aliens. They posted their findings to the preprint server arXiv on August 16. The research has not yet been peer-reviewed.

The scientists hypothesize that the Wow! signal may have resulted from a rare occurrence in space: the sudden brightening of a cold hydrogen cloud. They suggest a strong source of energy, such as a flare from a super-magnetized, extremely dense star called a magnetar, could have struck a cloud of hydrogen gas and caused it to glow brighter. The cloud could have emitted a laser-like beam of radiation in a phenomenon called a maser.

This proposed series of events is “a very rare kind of astrophysical anarchy,” writes Scientific American’s Robin George Andrews.

Over the decades since Ehman recorded the Wow! signal, scientists have come up with numerous ideas for its origin. One particularly controversial take came in 2016, when astronomers suggested the emission came from a passing comet. And in 2022, researchers ruled out one star as a source for the signal.

“I think we have probably the best explanation so far,” says lead author Abel Méndez, a planetary astrobiologist and director of the Planetary Habitability Laboratory, to Science News’ Lisa Grossman.

To reach their conclusion, Méndez and his co-authors—astrophysicists Kevin Ortiz Ceballos of the Center for Astrophysics, Harvard and Smithsonian, and Jorge Zuluaga of the University of Antioquia in Colombia—analyzed archived data collected by the former Arecibo Observatory in Puerto Rico.

They found that between February and May 2020, the observatory picked up multiple instances of radio activity similar to the mysterious signal from 1977. The locations of these signals corresponded to the sites of cold hydrogen clouds in space.

“I said, ‘Wait, wait, wait!’ That was the moment,” Méndez tells Science News. “If it was brighter for a moment, that would be it. That would be the ‘Wow!’ signal.”

The more recent data is dimmer than the Wow! signal, but Méndez tells New Scientist’s Alex Wilkins that’s because these hydrogen clouds were not illuminated by a magnetar. “When you do the calculation, they will become much, much brighter [if they were].”

This explanation remains a hypothesis, for now, and not all experts agree.

“He’s suggesting a phenomenon that has never been observed,” Search for Extraterrestrial Intelligence (SETI) astronomer Jason Wright, who was not involved in study, tells Science News. “The set of physical conditions is extremely delicate and specific, and it’s not clear if that’s even possible.”

Rest assured, the hypothesis still holds implications for aliens. If proven to be true, the phenomenon could guide future searches for extraterrestrial life—suggesting researchers should question whether similar signals are really aliens, or simply false positives from hydrogen clouds.

Margherita Bassi | READ MORE

Margherita Bassi is a trilingual storyteller and freelance journalist with a particular interest in ancient history, astronomy and human interest stories.