After searching 100,000 galaxies for signs of highly advanced extraterrestrial life, a team of scientists using observations from Nasa's WISE orbiting observatory has found no evidence of advanced civilisations in them.
The team also discovered some mysterious new phenomena in our own Milky Way galaxy.
"The idea behind our research is that, if an entire galaxy had been colonized by an advanced space-faring civilisation, the energy produced by that civilisation's technologies would be detectable in mid-infrared wavelengths," said lead researcher Jason T. Wright, assistant professor of astronomy and astrophysics at the Centre for Exoplanets and Habitable Worlds at Penn State University.
Freeman Dyson, a theoretical physicist, had proposed in the 1960s that advanced alien civilizations beyond Earth could be detected by the tell-tale evidence of their mid-infrared emissions.
It was not until space-based telescopes like the WISE satellite that it became possible to make sensitive measurements of this radiation emitted by objects in space.
Roger Griffith, researcher at Penn State and the lead author of the paper, scanned almost the entire catalogue of the WISE satellite's detections - nearly 100 million entries - for objects consistent with galaxies emitting too much mid-infrared radiation.
He also examined and categorized around 100,000 of the most promising galaxy images.
"This research is a significant expansion of earlier work in this area," said Brendan Mullan, director of the Buhl Planetarium at the Carnegie Science Centre in Pittsburgh.
"As we look more carefully at the light from these galaxies, we should be able to push our sensitivity to alien technology down to much lower levels and to better distinguish heat resulting from natural astronomical sources from heat produced by advanced technologies. This pilot study is just the beginning," Wright concluded.
The study will be published in Astrophysical Journal Supplement Series.