It has always been a great mystery whether or not we are alone in the Universe, so scientists have stepped up their efforts and searched 100,000 galaxies for signs of alien life, and they found... nothing.

While this may seem like a major disappointment, astronomers assert that they really were not surprised by coming up empty, and they haven't given up hope yet of finding far-away alien civilizations.

"This is a pilot project, and I would have been stunned to see aliens using all of the starlight in a galaxy somewhere," Jason T. Wright, an assistant professor of astronomy and astrophysics at Penn State University, who initiated the search, told the website Motherboard.

The 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 such a civilization did exist, it would emit tons 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 explained in a statement. "This same basic physics causes your computer to radiate heat while it is turned on."

The idea that advanced alien civilizations beyond Earth could be detected by their mid-infrared emissions was first proposed by theoretical physicist Freeman Dyson in the 1960s. However, it wasn't until space-based telescopes, like NASA's WISE satellite, were available that astronomers could begin looking for this evidence out in space.

"The idea behind our research is that, if an entire galaxy had been colonized by an advanced spacefaring civilization, the energy produced by that civilization's technologies would be detectable in mid-infrared wavelengths - exactly the radiation that the WISE satellite was designed to detect for other astronomical purposes," Wright added. (Scroll to read on...)

Since it first became operational, WISE has detected over 100 millions galaxies, but for this study scientists chose to look at the 100,000 most promising galaxies for signs of alien life. About 50 of those galaxies showed unusually high levels of mid-infrared radiation, and the researchers hope to further study these regions in more detail to reveal if the origin of their radiation results from natural astronomical processes, or an advanced civilization.

In any case, the fact that the team didn't detect any obvious alien-filled galaxies is even useful for their future research.

"Our results mean that, out of the 100,000 galaxies that WISE could see in sufficient detail, none of them is widely populated by an alien civilization using most of the starlight in its galaxy for its own purposes," Wright said. "That's interesting because these galaxies are billions of years old, which should have been plenty of time for them to have been filled with alien civilizations, if they exist. Either they don't exist, or they don't yet use enough energy for us to recognize them."

"This research is a significant expansion of earlier work in this area," added researcher Brendan Mullan. "The only previous study of civilizations in other galaxies looked at only 100 or so galaxies, and wasn't looking for the heat they emit. This is new ground."

NASA firmly believes that we are not alone in the Universe, and as this and other studies continue in their search for life beyond Earth, it seems that we may be getting closer to finding advanced civilizations.

"As we look more carefully at the light from these galaxies," said Wright, "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."

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