After searching 100,000 galaxies for the waste heat signatures emitted by highly advanced extraterrestrial life, a team of astronomers has found no obvious signs. But according to Jason Wright, the astronomer at Penn State who initiated the search, this hunt is just getting started.
"This is a pilot project, and I would have been stunned to see aliens using all of the starlight in a galaxy somewhere," Wright told me over the phone.
Pilot project though it may be, Wright's new study, which appears today in the Astrophysical Journal Supplement Series, is by far the largest search ever conducted for a Kardashev Type III supercivilization—one that spans its entire galaxy, harnessing the energy of billions of stars. If a K-3 civilization exists, it would be pouring tremendous amounts of heat into space as a byproduct of its industrial and technological activities.
"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 said. "This same basic physics causes your computer to radiate heat while it is turned on."
The notion that we might be able to detect aliens via their infrared heat signatures traces back to the 1960s, when theoretical physicist Freeman Dyson first proposed an awesome, if slightly insane, idea: That an advanced civilization might build a giant sphere around its star to collect and harness all of that star's energy. Those hypothetical megastructures, known as Dyson spheres, have since become a staple of science fiction, but they've also been the subject of several legitimate astronomical searches.
Early searches for Dyson spheres in the 1980s and early 90s turned up empty handed. But at the time, astronomers were hampered by the limitations of their telescopes, which struggled to resolve many confounding infrared heat sources, including interstellar dust.
It wasn't until space-based telescopes, like NASA's WISE Observatory, were available that it became possible to make sensitive measurements of the radiation emitted by distant objects. WISE performed an all-sky survey in 2010 that was able to resolve roughly 100,000 galaxies. Wright's team has been scouring this database for the telltale signs of extraterrestrial life ever since.
"When we look at these galaxies, we have to account for natural sources of infrared heat, such as star formation and dust," Wright told me. "We're now able to subtract these off and see if anything's left."
If a galaxy still appears suspiciously hot after natural sources have been accounted for, then it might just harbor a K-3. Wright's team found about 50 galaxies with unusually high levels of mid-infrared radiation, but, he says, no definitive evidence for advanced supercivilizations yet.
"Most of those fifty galaxies were already known to have very high rates of star formation," Wright told me. "But for three of them, no one has ever made the measurements, so we can't be sure."
Looking more closely at those three hot galaxies is a next step for the research team. Wright also hopes to continue pushing the infrared detection threshold up, so that we can begin searching for civilizations that use less astronomical amounts of energy.
"It's important to keep in mind that this study was looking for societies that are way beyond the norm," Seth Shostak, director of the SETI Institute, told me. "We're talking 100 billion billion times more energy than Homo sapiens uses. It's almost like saying there's no one in New York City who's dated all the girls in New York City."
Which is to say, even if galaxy-spanning K-3s are highly unlikely, there could still be plenty of civilizations out there.
"Some have made the argument that, if we don't see galaxy-spanning civilizations, then life is either unique to Earth—which seems super unlikely—or it's really really hard to put a colony on another star," Wright said. "If the latter is true, this work actually provides a good rationale for continuing to look at nearby star systems for radio communications."
And hey, maybe it's for the best if the universe is filled with other fledgling spacefarers, rather than a superintelligent supercivilization that can juice our little solar system like a AAA battery.
Top image: A false-color image of the mid-infrared emission from the Great Galaxy in Andromeda, as seen by Nasa's WISE space telescope. The orange color represents emission from the heat of stars forming in the galaxy's spiral arms. Image Credit: NASA/JPL-Caltech/WISE Team