The aliens are all hanging out on Dyson spheres 

So far no one has found evidence of intelligent aliens elsewhere in the cosmos. But if they do exist, they might be hanging out on Dyson spheres circling the husks of sunlike stars called white dwarfs scattered throughout the Milky Way, a new paper argues.

And that’s there we should be focusing our search for extraterrestrials, study co-author Ben Zuckerman, an emeritus professor of physics and astronomy at the University of California Los Angeles, told Live Science in an email. Based on what that search turns up, astronomers could estimate how many advanced civilizations lurk in the galaxy, he said. 

Any advanced civilization needs energy: for food, for transport, for conflict, for comfort and for convenience. Currently, Earth’s 7.8 billion people use around 580 million million joules of energy every year, equivalent to the energy output of almost 14,000 million tons of oil, according to The World Counts(opens in new tab). Indeed, almost all human energy comes from fossil fuels, as we lack the technological savvy to rely on the  largest generator of energy in the solar system: the sun.

If humans covered every square inch of Earth’ssurface with solar panels, that would generate more than 10^17 joules of energy per second. That would still be losing the majority of energy radiated by the sun, about 10^26 joules per second.

This is the motivation behind Dyson spheres, named for the famed physicist Freeman Dyson, who developed the idea in 1960. If an advanced civilization really wants to harness the awesome energetic output of their home star, they have to build megastructures to capture it, blocking out at least some of the star’s light and converting that energy into other useful things. Dyson’s original proposal of a solid sphere (with 100% solar coverage) doesn’t work because of stability issues, as it would be impossible to keep the star at the center and the entire sphere would disintegrate due to extreme tidal and rotational stresses. Even so, it’s easy to imagine an advanced species building rings or swarms of giant solar panel-covered structures to get the job done.

But no matter how advanced a species is, and how many Dyson sphere-like objects they build, they will have to contend with the fact that every star has a finite lifetime. If a civilization arose around a typical sunlike star, then someday that star will turn into a red giant and leave behind a cool white dwarf. That process will in turn roast its solar system’s inner planets and, as the white dwarf cools off, freeze the outer ones.

So  staying put on the surface of a planet is not a viable long-term option. That means any aliens could either pack up and leave, finding a new system to call home, or build a series of habitats that harvest the radiation from the remaining white dwarf.

According to a new paper written by Zuckerman and accepted in May for publication in the journal(opens in new tab) Monthly Notices of the Royal Astronomical Society, it seems unlikely that an alien civilization would choose to go through the trouble of traveling to a new star just to build a Dyson sphere. Thus, they’re only going to build these megastructures around their home stars, which will eventually turn into white dwarfs.

This allows scientists to make a direct connection between stellar lifetimes and the prevalence of Dyson spheres. So, Zuckerman reasoned, if astronomers look for Dyson spheres around white dwarfs and come up empty, that can help estimate how many advanced civilizations may exist in the galaxy. Here’s how the logic works: Astronomers have only measured a small fraction of all the white dwarfs in the galaxy. But if enough aliens decided to build Dyson spheres around their white dwarf homes, then we should see at least one Dyson sphere in our surveys. If we don’t see any at all, then that sets an upper limit on the number of alien  civilizations building Dyson spheres around white dwarfs. Of course there could be aliens who decide not to build Dyson spheres, or aliens that build spheres around other kinds of stars, but Zuckerman argues that over the age of the Milky Way the most likely outcome of advanced civilizations is to build a Dyson sphere around their white dwarf, and so we should focus our searches in that direction.

livescience