When searching for intelligent life, we are limited somewhat by the laws of physics, and our own circumstances and imaginations. We've only ever found intelligent (ish) life on one planet, so it makes sense to look for similar signals and signs that we produce and send out into the universe.

But we are in our infancy, technologically speaking, and are not even close to becoming a Type 1 civilization on the Kardashev scale of civilizations. At Type 1, a civilization is able to harness all the energy available to them on their planet (given at around 4 x 10¹⁹ erg per second) and use it for their own purposes. Type II civilizations are able to harness the energy of their star, e.g. by constructing a Dyson Sphere, theoretical megastructures constructed around stars built for this purpose. Type III civilizations, meanwhile, are alien civilizations capable of harnessing the energy of their whole galaxy. 

ent understanding of physics. Dyson spheres and Dyson swarms – megastructures placed around host stars to harvest their energy – have been a popular idea in our search for intelligent life. And they give us something to look for; extreme excess infrared radiation. We have potential candidates, but of course, none have been found, and some of them turned out to be hot dogs.

Is there something else we should be looking for? Are Dyson spheres unfeasible, unnecessary, inefficient, or a mixture of all three for any advanced civilization with huge power needs?

In a new paper, currently being reviewed for publication in Acta Astronautica and not yet peer reviewed, a team of researchers suggest there could be other types of power consumption we should be on the lookout for. In short, maybe we should look for "star eaters".

"We argue that the Kardashev scale is better understood as a 'luminosity limit' that describes the maximum capacity for a civilization to harvest luminous stellar energy across a given spatial domain, and we note that thermodynamic efficiency will always keep a luminosity-limited technosphere from actually reaching this theoretical limit," the team explains in their paper. 

"We suggest the possibility that an advanced technosphere might evolve beyond this luminosity limit to draw its energy directly from harvesting stellar mass, and we also discuss possible trajectories that could exist between Earth today and such hypothetical 'stellivores'."

While harvesting a star for energy using Dyson swarms would yield a lot of it, it would be a slow process, assuming incredibly high energy needs. The team proposes that advanced civilizations could instead consume stars for energy.

"A hypothetical idea by Vidal is that some accreting binary stars might actually be living or technological systems, with one compact object 'feeding' on its companion star to sustain metabolism. Some 'stellivores' may also have higher velocities with trajectories that are directed toward nearby stars for continued feeding," the team writes. "In such a case a stellivore would be observed as a binary system not accreting, but ejecting material out of its gravitational well, in order to generate thrust to travel toward another star."

These "stellivores" could be stationary, or even travel throughout the cosmos in order to feed off new stars when necessary. This may sound far-fetched – and it's certainly in the realms of sci-fi – but physicists have already proposed ways in which we could move our own Sun, should we ever need to do so.

These star-eaters may look like binary systems, and they propose that there may be a few ways to look for signs of life, as these stellivores would give off signatures beyond the luminosity limit.

"For stellivores, possible approaches toward testing this hypothesis include examining candidate traveling stellivore for possible signatures of a stellar engine, testing the goal-directedness of candidate traveling stellivore, testing whether accretion in candidate stationary stellivores is controlled, and applying biological metabolic scaling laws to candidate stellivores," the team explains in their conclusion. 

"Such efforts would be an important first step toward understanding the extent to which known stellar systems could reveal unusual properties that are closer to living systems than they first appear."

The paper is being reviewed for publication in Acta Astronautica, and is posted to pre-print server arXiv.