Famous “Wow!” signal could actually have been a natural space laser: ScienceAlert

An extremely powerful space laser could be the source of a mysterious signal that has puzzled astronomers for nearly 50 years.

No, it was not a warning shot from an alien civilization, but rather the work of a hydrogen cloud and a neutron star; the dense core of a massive star after a supernova hurled its entrails into space.

A new hypothesis suggests that such an object could, under the right circumstances, produce a signal like the surprised Astronomer Jerry Ehman on August 15, 1977, which prompted him to write the word “Wow!” on the printout.

The research, available as a preprint on arXiv, is currently being revised, but the findings so far are based on newly discovered evidence of similar signals and suggest that the team led by astrobiologist Abel Méndez of the University of Puerto Rico at Arecibo is on the right track.

“Our recent observations, conducted between February and May 2020, have revealed similar narrowband signals near the hydrogen line, albeit less intense than the original Wow! signal,” explains Méndez.

Ehman discovered this initial signal in data collected by Ohio State University's Big Ear radio telescope. It lasted just 72 seconds in total and was an extremely powerful burst of radio waves near the hydrogen line at 1420 MHz, the wavelength that hydrogen emits when it changes its spin direction.

Given the ubiquitous presence of hydrogen throughout the universe, some scientists speculate that light of this frequency could serve as an easily recognizable landmark in the electromagnetic spectrum that technologically advanced aliens might use to signal their presence.

If the famous pulse was indeed a “hello” from afar, it contained no modulation that could be decoded. The Wow! signal did not move, making it unlikely that it came from a nearby satellite, nor did it ever repeat in the way we would expect from an intentional transmission, precluding repeated observations with improved technology. In addition, many natural things emit radio waves at a wavelength of 1420 MHz, so while we cannot conclusively rule out aliens being around, it seems unlikely.

This leaves us with the search for a natural explanation for the signal, and that is exactly what Méndez and his team tried to do. Specifically, they searched archived data from the now-defunct “Radio Emissions from Red Dwarf Stars” (REDS) project at the Arecibo Observatory for short emissions of narrowband radio waves at a frequency similar to the Wow! signal.

They found four recordings worthy of further study. They came from near a tiny red dwarf called Teegarden's Star, just 12.5 light-years away. Although they were fainter than the Wow! signal, they were similar enough to provide clues to the origin of the famous signal.

According to the team's analysis, the signals near Teegarden's Star are associated with interstellar clouds of cold hydrogen. This suggests a possible mechanism for the Wow! signal: a powerful burst of radiation traveling through a cloud of cold hydrogen, stimulating the gas to produce a powerful pulse of radiation at about 1420 MHz.

The end product would be a natural, astrophysical microwave laser or Maserwhich produces an intense concentration of narrowband light at the hydrogen line that would look like the Wow! signal from a distance.

Because Teegarden's Star is a red dwarf, it is unlikely that it can produce a burst of radiation powerful enough to create an emission flash as strong as the Wow! signal, but other cosmic objects may be up to the task.

Neutron stars with extremely strong magnetic fields, called magnetars, can produce flares so powerful that we can detect them throughout intergalactic space. They are thought to be responsible for the mysterious signals known as fast radio bursts.

Another type of magnetar or neutron star, a so-called soft gamma repeater, could also be responsible. This is a type of star that regularly emits gamma or X-ray radiation. In any case, according to the team's model, the light pulse travels through the hydrogen, resulting in stimulated emission in the hydrogen band.

This is a very accurate explanation. Such a chain of objects and events would of course be quite rare; and even rarer if it were directed in our direction. So the hypothesis not only explains the signal, but also why we only saw it this one time.

“Our hypothesis takes into account all observed characteristics of the Wow! signal, introduces another source of false positives in the search for technosignatures, and suggests that this signal represented the first recorded astronomical maser flare in the hydrogen line,” the researchers write in their draft paper.

“We will continue with Arecibo Wow! and examine our extensive observational data sets from Arecibo REDS. Future studies will incorporate archival data from the Arecibo Observatory.”

The research results have yet to be submitted to a journal and are available on arXiv.