RATHER than searching for aliens phoning home, scientists are looking for signs of the homes themselves. A new project proposing that galaxy-spanning alien civilisations should generate detectable heat has turned up a few dozen galaxies that hold promise as harbours for life.
The best-known technique used to search for tech-savvy aliens is eavesdropping on their communications with each other. But this approach assumes ET is chatty in channels we can hear.
The new approach, dubbed G-HAT for Glimpsing Heat from Alien Technologies, makes no assumptions about what alien civilisations may be like.
“This approach is very different,” says Franck Marchis at the SETI Institute in California, who was not involved in the project. “I like it because it doesn’t put any constraints on the origin of the civilisation or their willingness to communicate.”
Instead, it utilises the laws of thermodynamics. All machines and living things give off heat, and that heat is visible as infrared radiation. The G-HAT team combed through the catalogue of images generated by the Wide-field Infrared Survey Explorer, or WISE, which released an infrared map of the entire sky in 2012. A galaxy should emit about 10 per cent of its light in the mid-infrared range, says team leader Jason Wright at Pennsylvania State University. If it gives off much more, it could be being warmed by vast networks of alien technology – though it could also be a sign of more prosaic processes, such as rapid star formation or an actively feeding black hole at the galaxy’s centre.
The team’s preliminary survey suggests that such galaxies are rare, but they are out there. “We have found several dozen galaxies giving out a superlative amount of mid-infrared light,” says Wright. About 50 of these are emitting more than half of their starlight in the mid-infrared, the team reports (Astrophysical Journal, doi.org/t82).
Could that mean we have already found alien civilisations that have spread across galaxies?
“If by ‘found them’ you mean that WISE detected the waste heat from them, then yes, that’s right – if these sorts of energy-hungry civilisations exist, WISE should have detected them,” Wright says. But identifying them is another story. “Distinguishing that waste heat from ordinary astrophysical dust will be very difficult in many cases, and proving it’s of alien origin will be even harder,” he says.
The next step is to look at the stars and galaxies that raised the infrared flag in the WISE survey and figure out if there are more ordinary processes at work.
“This effort is important because it tries to resolve the question of extraterrestrial life scientifically, using the laws of chemistry and physics that govern the universe,” says astronomer Geoff Marcy of the University of California, Berkeley.
Even if the effort doesn’t discover intelligent aliens, it is still doing solid science, says Marchis. “This work is useful no matter what because it’s cataloguing the mid-infrared of our stars and galaxies,” he says. “Like our exoplanet search and using rovers to look for microbes on Mars, this search for extraterrestrial life is driving useful science.”