In the 1960s, Russian astrophysicist Nikolai Kardashev published a paper outlining a classification system for potentially advanced alien civilizations. The Kardashev system, which numbers one to three, describes civilizations more advanced than Earth.
Type I civilizations can harness all the power available on their home planet, including solar energy reaching the planet, according to io9. Type II civilizations are capable of using all energy of their parent star, which may be accomplished by a Dyson sphere, a hypothetical megastructure that covers the sun. Finally, Type III civilizations are capable of utilizing all the stellar energy in their home galaxy.
According to Prof. Michael Garrett, of the Univ. of Leiden and the Netherlands Institute for Radio Astronomy, Type III civilizations are extremely rare, and may not exist in the local universe. Garrett’s findings are published as a letter in Astronomy & Astrophysics.
According to Garrett, Type III civilizations would give off heat waste detectable in mid-Infrared (IR) spectral region. Pennsylvania State Univ. scientists have identified several hundred candidate galaxies, “where unusually extreme mid-IR emission is observed,” according to the Netherlands Institute for Radio Astronomy.
Garrett focused on 93 sources for his study, but found that most, if not all, of the sources are likely caused by natural astrophysical processes. When comparing the galaxies’ mid-IR output with their radio emissions, they followed the mid-IR radio correlation, a rule that applies to most galaxies, according to Science Magazine.
The finding suggests the mid-IR emissions don’t stem from civilizations. The natural processes likely responsible are dust generated and heated by massive star formation.
“It’s very likely that the remaining systems also fall into this category, but of course it’s worth checking just in case,” said Garrett.
The good news: “It means we can all sleep safely in our beds tonight—an alien invasion doesn’t seem at all likely,” said Garrett.
However, the lack of evidence of Type III civilizations is jarring to Garrett. Perhaps such civilizations don’t adhere to the physical laws humans use to explain the physical universe. Perhaps they are so energy efficient that little heat waste is produced, he said.
