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. (More astronomy stories.)
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