Astronomy: is there alien life beyond our galaxy?

Seti, the search for extraterrestrial intelligence, has focused so far on looking and listening for signals from advanced civilisations within our own Milky Way galaxy. An alternative, more far-reaching approach is to scan the universe for whole galaxies that show signs of ultra-advanced technology.

Results from the first comprehensive galactic Seti survey are now in - and they can be described as ambiguous at best. No clear evidence of advanced life emerged from the search of 100,000 galaxies, using Nasa's Wide-field Infrared Survey Explorer (Wise) observatory, though a few showed tantalising signs worth further investigation.

"The idea behind our research is that, if an entire galaxy had been colonised by an advanced spacefaring civilisation, the energy produced by that civilisation'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 Wright of Penn State University, the project leader.

Freeman Dyson, the imaginative space theorist, proposed the idea in the 1960s but the technology to put it to the test has only recently become available. "Whether an advanced spacefaring civilisation 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.

The researchers first scoured all 100 million astronomical objects detected by Wise and then concentrated on the 100,000 most promising galactic images. About 50 of these had unusually high levels of infrared radiation, suggesting possible conversion of some stellar radiation to power alien technology. "Our follow-up studies of those galaxies may reveal if the origin of their radiation results from natural astronomical processes, or if it could indicate the presence of a highly advanced civilisation," he says.

But the failure to detect any obvious alien-filled galaxies is itself an interesting scientific result, according to Wright: "Out of the 100,000 galaxies that Wise could see in sufficient detail, none is widely populated by an alien civilisation using most of the starlight in its galaxy for its own purposes." He adds: "These galaxies are billions of years old, which should have been plenty of time for them to have been filled with alien civilisations . . . Either they don't exist or they don't yet use enough energy for us to recognise them."

Photograph: NASA

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