How to dominate the universe in three easy steps … 
 
 Step 1: Harvest all of your planet's resources. 
 
 Step 2: Harvest all of your nearest star's energy. 
 
 Step 3: Harvest all the energy from all the stars in your local galaxy; then move on to another galaxy. 
 
 Congratulations! Your species now has all the elbow room it needs to grow into a universal superpower. 
 
 That's one Russian astronomer's perspective, anyway. Astrophysicist Nikolai Kardashev first proposed these three phases (called Level I, II and III) of galactic expansion — which he referred to as the three "types" of technologically advanced civilizations — in 1962 as a way to measure the energy consumption of increasingly powerful societies. Recently, a paper posted June 13 to the preprint journal arXiv.org has revived Kardashev's model and added a new, apocalyptic twist. [13 Ways to Hunt Intelligent Aliens] 
 
 According to the author of the paper, Dan Hooper — a senior scientist at the Fermi National Accelerator Laboratory in Illinois and a professor of astronomy and astrophysics at the University of Chicago — harvesting energy from distant stars isn't just the best way to increase a civilization's available resources. It's also the only way to prevent the ever-expanding universe from leaving that civilization totally alone in the vastness of space. (This study has yet to be peer-reviewed.) 
 
 "The presence of dark energy in our universe is causing space to expand at an accelerating rate," Hooper wrote in the new paper. Over the next approximately 100 billion years, the stars beyond our Local Group, or a group of gravitationally bound galaxies that includes the Milky Way, will fall beyond the cosmic horizon, meaning an observer here could never retrieve information from them over the course of the age of the universe. 
 
 At that point, "the stars become not only unobservable, but entirely inaccessible, thus limiting how much energy could one day be extracted from them," Hooper wrote in the paper. 
 
 In other words, if humans hope to meet aliens in distant galaxies, it'll be a race against dark energy, that mysterious force thought to be uncontrollably stretching our universe farther and farther apart. 
 
 That, of course, is how we'll find the aliens. 
 
 Any advanced civilization worth their starships would understand the grim reality of universal expansion, Hooper wrote, and they wouldn't just sit around idly while the universe literally passed them by. Rather, they would capture stars from other galaxies, reel them in and harvest their energy first, before those stars (and their energy) became inaccessible forever. [12 Possible Reasons We Haven't Found Aliens] 
 
 "Given the inevitability of the encroaching horizon, any sufficiently advanced civilization that is determined to maximize its ability to utilize energy will expand throughout the universe, attempting to secure as many stars as possible before they become permanently inaccessible," Hooper wrote. 
 
 So, how do you lasso a star in the first place? Scientists and science-fiction authors alike have pondered this question for decades, and their favored answer is this: Throw a giant net around it, of course. 
 
 This net wouldn't be made of twine or even metal, but of satellites — a swarm of millions of solar-powered satellites known as "Dyson spheres." Such a colossal cloud of harvesters could permanently hover around a star, beaming energy back to a nearby planet — or, as Hooper proposed in his new paper, actually use that star's energy to accelerate the whole ball of fire back toward the planet that wanted to use it. 
 
 This may seem like a tall order for humans, who are still bumbling around Level I of Kardashev's scale. (Carl Sagan placed us at about a 0.7 in 1973). But some scientists think there could be alien civilizations thousands, or even millions, of years older than ours who are already well into their Level III, star-harvesting phase. 
 
 And if another civilization has indeed begun rearranging the stars, it may not be long before Earthlings notice them, Hooper wrote. 
 
 "Those stars that are currently en route to the central civilization could be visible as a result of the propulsion that they are currently undergoing," Hooper wrote. "Such acceleration would necessarily require large amounts of energy and likely produce significant fluxes of electromagnetic radiation." 
 
 Beyond watching for those stars being dragged unceremoniously across distant galaxies, astronomers could also keep an eye out for the unusual galaxies that have had their prime stars ripped away from them, Hooper wrote. 
 
 These hypothetical, star-harvesting aliens will probably be picky, Hooper noted: Teeny-tiny stars, hundreds of times smaller than Earth's sun, wouldn't produce enough radiation to be useful; significantly larger stars, on the other hand, would likely be too close to going supernova to be used as a viable battery. Only stars with a mass about 20 to 100 times the mass of our sun would be viable candidates for capturing and hauling back to the home galaxy, Hooper said. And because solar objects in that mass range radiate certain wavelengths of light more than others, alien star harvesting would show up in the light signatures from these galaxies. 
 
 "The spectrum of starlight from a galaxy that has had its useful stars harvested by an advanced civilization would be dominated by massive stars and thus peak at longer wavelengths than otherwise would have been the case," Hooper said. 
 
 Humans likely don't have precise enough instruments yet to detect these unusual light signatures beaming from the depths of the universe, Hooper wrote. Hopefully, astronomers will develop them before our sun becomes another flaming marble in some distant civilization's collection. 
 
 Originally published on Live Science. ||||| A pioneering infrared scan of 100,000 galaxies by Penn State astronomers has failed to detect any signs of galaxy-spanning extraterrestrial supercivilizations. This result, though very preliminary, may be a sign that aliens aren't capable of conquering entire galaxies. 
 
 Above: A false-color image of the mid-infrared emission from the Great Galaxy in Andromeda, as seen by Nasa's WISE space telescope. The G-HAT team used images such as these to search 100,000 nearby galaxies for unusually large amounts of this mid-infrared emission that might arise from alien civilizations. Caption and image credit: NASA/JPL-Caltech/WISE Team/Penn State/Roger L. Griffith et al. 
 
 Back in the 1960s, Russian cosmologist Nikolai Kardashev devised the famous scale that now bears his name . He proposed a simple numbering system — from one to three — that can be used to classify hypothetical alien civilizations according to the amount of energy at their disposal. According to the scale, a K1 civ has captured the entire energy output of its home planet, while a K2 civ has tapped into all the power produced by its home star. 
 
 But then there are K3 civs — so-called supercivilizations — who have tapped into virtually all of the energy produced by their own galaxy. As study co-author Jason Wright told io9: "Type III civilizations in the sense that Nikolai Kardashev originally defined them, were 'maximal' energy users: they command all of the starlight in their galaxy." 
 
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 This could be accomplished by ETIs in any number of ways, including vast complexes of Dyson spheres and the establishment of Matrioshka Brains. 
 
 K3 civilizations should be reasonably easy to detect from a distance. According to fundamental thermodynamics, the energy pulled in by a K3 civ must still be radiated away as heat in the mid-infrared wavelengths. These galactic-scale signatures, though far away, can still be detected from Earth. 
 
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 Seeking Alien Signatures 
 
 With this in mind, a team of astronomers from Penn State recently completed a survey, known as the Glimpsing Heat from Alien Technologies Survey (G-HAT), of 100,000 galaxies to see if they could find traces of galaxy-spanning supercivilizations. Their results now appear in the Astrophysical Journal. 
 
 The G-HAT team, led by postbaccalaureate researcher Roger Griffith, analyzed practically the entire catalog of detections made by NASA's WISE orbiting observatory. That's nearly 100 million entries. The researchers honed this list down to ~100,000 of the most promising candidates, looking for objects consistent with galaxies emitting too much mid-infrared radiation. 
 
 No obvious alien-filled galaxies were detected. 
 
 "We have shown that among the 100,000 galaxies that WISE can resolve, none of them contain such civilizations," Wright told io9. "This doesn't mean, however, that there are not galaxy-spanning civilizations in any of those galaxies, just that if there are, they aren't using most of the starlight for their own purposes." 
 
 That said, 50 galaxies did feature higher-than-usual levels of mid-infrared radiation. Further analysis will be required to determine if they're caused by some natural astronomic process, or if they're an indication of highly advanced extraterrestrial civilizations. 
 
 Whither K3? 
 
 This poses a bit of a problem for astrobiologists. Back in 1975, astronomer Michael H. Hart conjectured that super-advanced aliens should be able to colonize an entire galaxy within a reasonably short amount of time (at least from a cosmological perspective). Either that or humanity is alone in the Milky Way. It's this line of reasoning that led the Penn State researchers to conduct their inter-galactic survey. 
 
 "There has been a line of argument, originating with Michael Hart, that there should not be any advanced civilization in the Milky Way, because if there were, they would have taken over the entire galaxy by now," Wright told io9. "If this is correct, then our search for civilizations spanning other galaxies is the best approach." 
 
 Wright concedes that there may be a flaw in this reasoning, adding that many respected SETI researchers believe it's incorrect. 
 
 "So if, even as we refine our techniques, we continue to find no hint of intelligent life pandemic to other galaxies, this would strengthen the arguments of those who disagree with Hart's argument, and make searches within our own Milky Way an even more promising venue," he added. 
 
 The Search Continues 
 
 The next step for the G-HAT team is to scale things down a bit to see if less energy-intensive civilizations might exist in these galaxies. This is where Carl Sagan's adjunct to the Kardashev Scale might come in handy. 
 
 "On Sagan's scale, we want to push down from Type 3.0 to Type 2.9 or 2.8," says Wright. "That is, search for civilizations using 10% or even 1% of the starlight in a galaxy." 
 
 Encouragingly, the new study shows that WISE has the sensitivity and resolution to do this, but as Wright told io9, it would require careful examination of the light from these galaxies across the full range of the electromagnetic spectrum, and not just the emission WISE sees. 
 
 Also, the researchers want to extend their method to K2 civilizations. In other words, they want to search for Dyson spheres and/or other megascale artifacts produced by advanced aliens. 
 
 "This will require us to be able to distinguish distant, dusty giant stars from nearby, Sun-like stars with much of their starlight being collected by an advanced civilization," says Wright. "This is very hard because it requires spectra or distance measurements, which we do not have for most stars — but the ESA space telescope GAIA will measure distances to all of the nearby stars, making this search possible for the first time. We look forward to using those data to extend our search to the Milky Way." 
 
 Read the entire study at the Astrophysical Journal: “The Ĝ Infrared Search for Extraterrestrial Civilizations with Large Energy Supplies. III. The Reddest Extended Sources in WISE.”. ||||| Ancient extraterrestrial civilizations, millions of years older than humanity, would need enormous amounts of energy. By creating a swarm of satellites in a spherical shell, they could harness much of the power of their star. 
 
 Science fiction author Olaf Stapledon described spherical, energy-trapping alien structures in his 1937 novel "Star Maker": 
 
 "Not only was every solar system now surrounded by a gauze of light traps, which focused the escaping solar energy for intelligent use, so that the whole galaxy was dimmed, but many stars that were not suited to be suns were disintegrated, and rifled of their prodigious stores of sub-atomic energy." 
 
 Incredible Technology: How to Search for Advanced Alien Civilizations 
 
 Recalling Stapledon's description, physicist Freeman Dysonproposed similar structures in a scientific paper in 1960. Dyson realized that alien civilizations could be recognized by their waste heat, which would be detectable as infrared radiation. Dyson proposed that really advanced civilizations would re-engineer their solar systems, perhaps dismantling planets to form a shellof satellites around their star to capture its energy. [13 Ways to Hunt Intelligent Aliens] 
 
 Astrophysicist Nikolai Kardashev proposed in 1962 that very old and advanced civilizations would be of three types: 
 
 A Type I civilization harnesses all the resources of a planet. Carl Saganestimated that Earth rates about 0.7 on the scale. 
 
 A Type II civilization harnesses all the radiation of a star. Humans might reach Type II in a few thousand years. 
 
 A Type III civilization harnesses all the resources of a galaxy. Humans might reach Type III in a few hundred thousand to a million years. 
 
 A solid shell around a star would be gravitationally unstable, and would probably require more material than all of the planets of a solar system could provide. Instead, practical Dyson sphereswould be made from millions of individual solar-collecting satellites. 
 
 Solar sails could remain in place by balancing against the pressure of light from the sun. The satellite would not be in orbit, it would actually hover in space. Such a satellite is called a "statite." Rings of statites would form a cloud around the star, collecting its energy and beaming it back to the home planet. 
 
 Dyson spheres and other mega-structures appear frequently in science fiction. In his 1970 novel "Ringworld," Larry Niven features a ring-shaped artificial structure girdling an alien star. In the 1992 “Star Trek: The Next Generation” episode "Relics," the starship Enterpriseencounters a Dyson sphere in the form of a rigid shell surrounding a star. 
 
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– Watch out for stars moving across galaxies or losing power—it could be aliens gathering energy before the lights go out. Dan Hooper, an astronomy and astrophysics professor at the University of Chicago, posted a paper in the preprint journal arXiv.org arguing that aliens in far-off galaxies may be sucking energy from stars to offset risks posed by an expanding universe, LiveScience reports. "The presence of dark energy in our universe is causing space to expand at an accelerating rate," writes Hooper. "As a result, over the next approximately 100 billion years, all stars residing beyond the Local Group [of galaxies including the Milky Way] will fall beyond the cosmic horizon and become not only unobservable, but entirely inaccessible, thus limiting how much energy could one day be extracted from them." Therefore, he argues, an advanced civilization may use something like "Dyson spheres"—an imagined solar-powered satellite dating back to 1930s science-fiction, notes LiveScience—to harvest a star's energy or use that energy to move it closer to home. Hooper hinges his case on the work of Russian astronomer Nikolai Kardashev, who argued in 1962 that technologically advanced civilizations would expand via three steps: harvesting resources of their planet, then the nearest star, then all stars in the galaxy and nearby galaxies. So how to spot energy-grabbing aliens? Massive stars emanate certain light wavelengths, which will appear in galaxies' light signatures if stars are drained energy—that is, when humans have powerful enough instruments to detect it.