The Sloan Digital Sky Survey telescope at night. Image credit: Patrick Galume

It’s a bold claim: A Canadian astronomer says he’s found not just one alien signal from a far-away world, but 234 of them. Ermanno Borra, an astronomer at Laval University, together with his graduate student Eric Trottier, has combed through data from 2.5 million stars, provided by the Sloan Digital Sky Survey. Buried in the light from some of those stars was an unusual signal—pairs of light pulses, less than 2 trillionths of a second apart, with no obvious natural origin.

“The strange thing is that, out of more than 2 million stars, we only found it [the pulses] in 234 stars—and those stars look a little bit like the Sun,” Borra tells mental_floss. He adds that he and Trottier were careful to rule out the most obvious causes of a false signal—instrument error and faulty data analysis. In their paper [PDF], uploaded to the ArXiv server earlier this month and subsequently published in Publications of the Astronomical Society of the Pacific, they also point out that if the signal were due to a systematic error, it would show up in all stars, and in galaxies and quasars; instead, it seems to only show up in Sun-like stars. They also considered the possibility that the signal is caused by atmospheric phenomena on the surface of the stars.

“The signal is real,” Borra says. “Still, it’s not 100 percent certain that it comes from ETI [Extraterrestrial Intelligence].” He says that that’s “the most likely explanation, but of course, more work needs to be done.”

Borra had speculated in a 2012 paper that high-powered lasers were a plausible means for advanced civilizations to communicate, and that if aliens wanted to announce their presence to Earthlings, they could aim a laser in our direction and use a pulsed signal to get our attention. Such signals, he argued, could be picked out by a careful analysis of the spectra collected by all-sky star surveys. Their new paper, he says, is consistent with that idea.

In the new paper, they report pairs of optical pulses coming just 1.65 picoseconds apart (one picosecond is one trillionth of a second). The pairs themselves appear to come a few milliseconds apart, but not in any specific pattern.

The astronomical community is reacting with measured skepticism.

“It’s a signal that’s not like anything we’re familiar with in nature—but then the question is, might it be caused by something other than ET?” asks Douglas Vakoch, an astronomer and president of METI International, a research and educational institute dedicated to both SETI and METI. (SETI stands for "search for extraterrestrial intelligence"; in METI, the M stands for "messaging.")

Vakoch tells mental_floss that for him, the strangest part of Borra’s study is the fact that each of the 234 stars is sending exactly the same kind of pulses, with the same periodicity. If these signals originate with alien civilizations, he muses, then they’ve apparently formed a “galactic club” that’s announcing its presence in a coordinated way. He considers this a somewhat far-fetched idea.

Further insight will come when astronomers with the Breakthrough Listen Initiative use the 2.4-meter telescope at Lick Observatory in California to see if they can replicate the observation. If they succeed, says Vakoch, it “still wouldn’t tell you that it’s ET, but at least it would be a confirmation [of the signal].”

He recalls that back when pulsars were discovered, the first of these strange radio-wave sources, spotted in 1967, was playfully dubbed “LGM-1,” for “Little Green Men.” We now know that pulsars are rapidly spinning, dense stars that periodically send bursts of radio waves toward Earth.

The lesson is that what looks alien might just be nature doing something we’re not familiar with. “The general mindset in SETI is that, before you say it’s an extraterrestrial intelligence, you have to think really creatively about what the natural explanations might be—and I think it’s way too early in the game to jump to the conclusion that it’s extraterrestrial intelligence,” says Vakoch. Still, he says: “It’s good that this data is out there, so we can follow up on it.”