Lack of 'civilisation footprint' suggests aliens are intellectually challenged
Perhaps we should breathe a sigh of relief - super-advanced aliens with the ability to harness the power of whole galaxies do not appear to exist, at least in our corner of the universe.
Scientists carried out a systematic search for evidence of "Kardashev Type III" civilisations so advanced that next to them humans might be considered barely intelligent apes.
Humans have not even achieved "Type I" status on the Kardashev scale, let alone Type II or Type III.
Faced by a Type III invasion, we would not stand a chance. But luckily no such God-like beings are remotely within range of our solar system, according to the new research.
The Kardashev scale was drawn up in 1964 by Russian astronomer Nikolai Kardashev as a method of rating a civilisation's level of technological advancement based on the way it uses energy.
By definition, Type III civilisations can access the energy of entire galaxies. They may, for instance, be able to tap into the energy released by supermassive black holes or active galaxies known as quasars.
Such a civilisation would be expected to produce a large amount of waste heat that should be detectable by astronomers.
Scientists have now conducted a search for such a Type III civilisation "footprint" among several hundred nearby galaxies - and discovered nothing that cannot be explained naturally.
Professor Michael Garrett, from the Netherlands Institute for Radio Astronomy, said: "Original research .. has already told us that such systems are very rare, but the new analysis suggests that this is probably an understatement, and that advanced Kardashev Type III civilisations basically don't exist in the local universe.
"In my view, it means we can all sleep safely in our beds tonight - an alien invasion doesn't seem at all likely!"
The vast majority of the galaxies investigated - shortlisted from a total of around 100,000 - produced emissions more likely to be generated by star formation rather than aliens.
A few candidate galaxies remain whose emission profiles are harder to explain, but Prof Garrett believes they too will eventually be crossed off the list.
"Some of these systems definitely demand further investigation, but those already studied in detail turn out to have a natural astrophysical explanation too," he said. "It's very likely that the remaining systems also fall into this category, but of course it's worth checking just in case."
Prof Garrett plans to use the same technique to look for less advanced Kardashev Type II civilisations with the ability to harness the energy of whole planets and stars within a galaxy.
Such a civilisation would still be far more advanced than our own, but possibly more common.
The human race is estimated to be at least a century or two away from attaining the level of a Type I civilisation, one which has mastered nuclear fusion and renewable energy sources such as solar power.
While it may be good news for the rest of us, from a scientific standpoint Prof Garrett finds the apparent lack of Type III civilisations disappointing.
He added: "It's a bit worrying that Type III civilisations don't seem to exist. It's not what we would predict from the physical laws that explain so well the rest of the physical universe. We're missing an important part of the jigsaw puzzle here.
"Perhaps advanced civilisations are so energy efficient that they produce very low waste heat emission products - our current understanding of physics makes that a difficult thing to do.
"What's important is to keep on searching for the signatures of extraterrestrial intelligence until we fully understand just what is going on."
The research is due to appear in the journal Astronomy & Astrophysics.