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.

Catch a star by the toe

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."

Redecorating the galaxy

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.