Stellar spider engine: Are aliens using their host stars as ‘spacecraft’?

With these endless possibilities in mind, Dr. Clément Vidal, a philosopher from the Vrije University in Brussels, Belgium, recently proposed a highly unconventional hypothesis. 

Vidal believes an intelligent alien species could use its host star as a spacecraft. Moreover, it could be transporting its entire solar system to other stars. The goal? To “eat” those stars and harvest their energy, Vidal explained in an interview with Interesting Engineering.

Asking the big questions

Are we alone in the universe? For centuries, philosophers have posed the question. More recently, the scientific community has taken up the mantle. For example, NASA’s James Webb Space Telescope probes distant worlds for signs of alien life. Meanwhile, the Search for Extraterrestrial Intelligence (SETI) Institute was founded with the goal of searching for evidence of technological civilizations beyond Earth.

On his website, Vidal notes that he likes to consider the “big questions.” That’s clear in his new “Spider Stellar Engine” paper. In it, he proposes that alien civilizations could steer their host stars throughout the universe. He also suggests several signatures we could look out for to prove his hypothesis.

In his paper, Vidal suggests that these moving star civilizations would turn their planetary system into a “spacecraft.” In theory, a civilization could continue to function. At the same time, its star system is propelled through space at immense speeds – we are flying through the interstellar medium at hundreds of thousands of kilometers per second.

Vidal hypothesizes that an intelligent extraterrestrial civilization might have discovered how to eject material away from their host star. By ejecting this material in a specific direction, it would create thrust. This would propel the star and its surrounding planets in a specific direction.

“The essence of generating thrust is to expel matter in the opposite direction of the desired motion,” Vidal explained to IE. It’s a simple notion that can be demonstrated in a classroom or on the street: “You can actually experiment this fundamental law formalized by Newton by standing on a skateboard with a large bottle of water, and throwing it backwards: the skateboard will move forward.” 

Could binary star systems be the key?

Vidal isn’t the only one who has suggested that extraterrestrial civilizations could be moving their stars. Astronomers estimate roughly 1,000 so-called “hypervelocity stars” flying through our galaxy. However, efforts to connect these to a technological civilization have come up empty-handed.

In his paper, Vidal focuses on the potential of binary star systems. “Since about half the stars in our galaxy are in binary systems where life might develop too, we introduce a model of a binary stellar engine,” he wrote in his paper, published in the pre-print server arXiv.

“The idea of a binary stellar engine came in several steps over several years,” Vidal explained to IE. “First, when I started to study the behavior of binary systems in accretion, I thought they looked like a metabolism: a compact object sucks in plasma from a companion star, in an irregular fashion, and ejects matter out of its system.” 

“All living things do metabolize: they extract energy from their environment, use it for survival and maintenance, and generate waste products,” he continued. “I thought: could it be a living system at a stellar scale? I called this hypothesis the “stellivore hypothesis”.”

“The next challenge is to test the hypothesis,” Vidal said. “A natural expectation is that living systems want to survive, and finding food is critical for this goal. So I thought that if a stellivore has almost completely eaten its star, it would naturally aim to go towards another star to eat it.”

Spider pulsars

This line of thought led Vidal to hone in on spider pulsars. Pulsars are the spinning dense cores of dead stars. They are neutron stars that spin so fast that they produce rotating radiation beams. Spider pulsars are a class of millisecond pulsars that get their name because they damage their small companion stars.

According to the philosophy professor, these perfectly fit the bill. They are binary systems with a very low-mass companion star – in the 0.01 to 0.7 solar masses range. Could these companion stars have been purposefully eaten away by an alien civilization?

In another paper, Vidal posed the question: Are spider pulsars goal-directed? He asked whether they were searching for other stars to consume. In the newer paper, he dived into the possible mechanisms these spider pulsars – driven by an advanced civilization – could use to accelerate, decelerate, and steer. 

How would binary stars navigate?

The idea behind a binary star stellar engine is that it would steer by ejecting power from the stars at specific moments in their orbits. An alien civilization could achieve this by several means, including using asymmetric magnetic fields and an advanced device that causes uneven heating on the star’s surface.

“The main idea of a binary stellar engine is to generate thrust by ejecting mass from the small companion star in the opposite direction of motion,” Vidal told IE. “What is unusual due to the binary nature of the engine is that mass needs to be ejected not continuously (as with most human-made rockets), but in a pulsed fashion, only when the companion star is backward with respect to the desired motion.” 

“The perk with this method of timed propulsion is that you can go in any direction in the orbital plane, simply by timing the evaporation of the companion star,” he continued.

All of this raises the question: How would an alien civilization survive while navigating interstellar space? According to Vidal, there are several possibilities. Crucially, we must be open to the idea that life in a distant star system might differ greatly from our own. This is especially true if that life is advanced enough to harness its host star as a transportation medium. 

“Regarding the issues of planets, their masses are negligible in comparison to a neutron star, so they would just follow along,” Vidal explained. “However, as far as I know spider pulsars do not have planets, and the stellivore hypothesis does not require that life stays bound to a planet, it could be a technological, or “postbiological” kind of life.” 

Can we prove aliens are driving entire star systems?

Vidal’s hypothesis will be incredibly interesting to anyone curious about the possibility of life far beyond Earth. However, alien hypotheses are of little value without specific avenues of research to follow. Thankfully, Vidal does point toward specific instances that are worth more investigation.

According to Vidal, thrust maximization might be key. “An engineered spider stellar engine would want to maximize its thrust by aligning the thrust with the direction of motion,” he explained. “In terms of astronomy, this translates to finding an alignment between the orbital plane and the proper motion vector. There would be no natural reason for such an alignment by chance.” 

Vidal also points to a few spider pulsar observations that merit another look. The redback pulsar J2043+1711, for example, has decelerated, and this could be due to its approach to another star. The black widow J1641+8049, meanwhile, seems to have decelerated significantly. Vidal says this “requires a follow-up to check whether this is real or whether it could have been a measurement error.” 

And if we find that an alien civilization is likely navigating its entire star system through interstellar space, what next? Communication at such distances is unthinkable with existing technologies. Perhaps the greatest value would be in the way this discovery would fire up our imaginations. As Vidal explained, the stellar engine idea “may also be scaled down to propose new designs for planetary defense purposes or as an additional advanced propulsion method for deep space missions.”