An extensive search for intelligent life elsewhere in the Milky Way has failed to find any traces of alien activity, indicating that we may indeed be the sole inhabitants of our galaxy. After targeting millions of stars and hundreds of exoplanets, researchers were unable to detect a single technological signal of extraterrestrial origin.

The lonely search is detailed across four separate studies published over the course of the past nine years, the most recent of which has just been made available as a preprint and is awaiting peer review. In each installment, the researchers describe their search for technosignatures elsewhere in the Milky Way using the Murchison Widefield Array in Australia.

Technosignatures are indications of the use of technology, and their discovery in outer space would almost certainly represent success in the Search for Extraterrestrial Intelligence (SETI). While these signatures can take many forms, the study authors specifically chose to focus on low-frequency radio waves, as these are likely to be among the first electromagnetic signals developed by an alien civilization.

“On Earth, low-frequency radio signals, like those used by FM radio, are a ubiquitous choice for communications,” write the authors of the most recent study. In order to produce such a signal, an alien civilization “would only need to be able to build a big dish,” which leads the researchers to conclude that “the most delectable signal from another planet would be a powerful military satellite.”

The first three studies in the series looked for low-frequency radio waves emanating from the galactic center (GC), the Orion Molecular Cloud and the Vela supernova remnant, yet found nothing. In the latest chapter, researchers again turned their attention to the GC, yet this time scanned a wider portion of the sky.

“The Galactic Centre (GC) is a prime SETI target as the line of sight toward the GC has the largest integrated count of Galactic stars for any direction,” they write. Furthermore, “the fraction of stars with a habitable planet is greatest in the inner regions of the Galaxy,” all of which points to the GC as the most likely home for alien life.

After targeting their search on 144 exoplanetary systems in the GC, the study authors then conducted a blind survey of 3.3 million stars. Sadly, though, they found diddly squat.

“No plausible technosignatures are detected,” they explain.

As disappointing as this finding may be, it doesn’t categorically prove that we are all alone in our galaxy, as it’s possible that life may exist in an as-yet unscanned region of our cosmic neighborhood or that we simply haven’t developed the right technology to detect it.

Still, the radio silence reported in these four studies deepens the frustratingly inexplicable conundrum known as the Fermi paradox, which describes the apparent discrepancy between our lack of contact with aliens and the high probability that extraterrestrial civilizations exist. After all, there are so many potentially inhabitable planets in the universe, and given the age of our galaxy, it’s highly likely that someone, somewhere, would have developed the technology to colonize other planets by now.

The fact that Earth has never been visited by such a civilization – at least, not as far as we know – is therefore rather baffling, although a number of speculative explanations have been mooted. For instance, some scientists believe that the age of the universe makes it unlikely for multiple intelligent civilizations to exist at the same time, which means we may have simply missed the aliens like passing ships in the night.

Whether our galactic cousins are avoiding us, haven’t developed the technology to contact us, or simply don’t exist, researchers here on Earth are determined to keep up the hunt in the hope that someday, someone gives us a sign.

[H/T: Universe Today]