A search of 100,000 galaxies for a particular sign that might indicate the presence of an advanced extraterrestrial civilization has come up empty, researchers say.
Scientists at Penn State University analyzed data from a NASA satellite, the Wide-field Infrared Survey Explorer or WISE, looking for signs of infrared radiation that a star-voyaging civilization might generate.
"The idea behind our research is that, if an entire galaxy had been colonized by an advanced spacefaring civilization, the energy produced by that civilization's technologies would be detectable in mid-infrared wavelengths - exactly the radiation that the WISE satellite was designed to detect for other astronomical purposes," says Jason T. Wright, an astronomer and astrophysicist at the university's Center for Exoplanets and Habitable Worlds.
The researchers have described their efforts, dubbed the Glimpsing Heat from Alien Technologies Survey, in the Astrophysical Journal Supplement Series.
Fifty years ago physicist Freeman Dyson suggest mid-infrared emissions might be significant evidence of an advanced alien civilization's activities, but it was impossible to make measurements of such radiation in space until the advent of space telescopes like the WISE instrument.
Almost 100 million WISE observations were examined for evidence of galaxies emitting more infrared radiation than natural processes might account for, out of which about 100,000 promising galactic images were identified.
Previous efforts to find civilizations in other galaxies only looked at about 100 or so candidates, the researchers note.
Of 100,000 possibilities from the WISE survey, around 50 showed unusual radiation patterns, but whether they are natural anomalies or evidence of alien civilizations cannot currently be determined, the researchers say.
"Our results mean that, out of the 100,000 galaxies that WISE could see in sufficient detail, none of them is widely populated by an alien civilization using most of the starlight in its galaxy for its own purposes," says Wright.
In the billions of years of these galaxies' life spans there ought to have have been ample time for the rise of advanced alien civilizations using advanced technology, if in fact any exist, he says.
"Either they don't exist, or they don't yet use enough energy for us to recognize them," Wright says.
Still, the theory is sound enough for the search to continue, the researchers suggest.
"Whether an advanced spacefaring civilization uses the large amounts of energy from its galaxy's stars to power computers, space flight, communication, or something we can't yet imagine, fundamental thermodynamics tells us that this energy must be radiated away as heat in the mid-infrared wavelengths," Wright says.