Stellar J-harvesting technosignature proposed in search for slow-spinning stars

A new arXiv preprint proposes a stellar J-harvesting technosignature, a way to search for advanced technology by looking for stars whose spin may have been deliberately slowed. The idea matters for the search for extraterrestrial intelligence because such systems could be much harder to detect than a Dyson swarm, according to the paper.

Sahin Torlakcik, identified by Universe Today as a Turkish high school student, describes a hypothetical system that would draw energy from a star’s rotational angular momentum rather than from its light. The preprint, titled “Stellar J-Harvesting: a novel angular momentum technosignature and first search in the Kepler field,” is available on arXiv.

What is stellar J-harvesting?

Stellar J-harvesting is the proposed extraction of a star’s angular momentum, the physical quantity tied to its rotation. In practical terms, the paper asks whether an advanced civilization could slow a star’s spin and use that process as an energy source.

The concept differs from the better-known Dyson sphere idea, which involves collecting a star’s emitted light. Torlakcik argues in the preprint that a spin-harvesting system would need less building material and would create waste heat millions of times lower than the star’s luminosity, which could make it hard to identify in infrared surveys.

The paper lays out several possible engineering approaches, all based on electromagnetic coupling rather than direct friction. One option would place a large conducting structure in the stellar wind, where Alfvén-wave coupling could transfer some of the star’s angular momentum into the structure.

Another option would use a large electrically conductive ring in orbit at roughly 1 AU, the Earth-Sun distance. The preprint says such a ring could interact with the star’s magnetic field through Lorentz-force coupling and draw angular momentum from the star.

A third proposal, called a synchrotron spin-down array, would accelerate charged particles in the stellar wind to near-relativistic speeds. Torlakcik writes that the resulting synchrotron radiation could create a reactive torque on the array and slow the star’s rotation, while also producing possible radio-wave or X-ray signatures depending on the system’s speed and magnetic field strength.

Which stars did the first search flag?

Torlakcik applied the idea to stars in the Kepler field, sorting them by color and surface gravity and filtering out natural false positives such as subgiants and pre-main-sequence stars, according to the preprint. The resulting sample contained 6,725 FGK main-sequence stars.

Two G-type main-sequence stars stood out in that search: KIC 67606183 and KIC 9834255. The paper gives their rotation periods as 61 and 65 days, compared with 5 to 10 days for stars of similar age.

The preprint does not claim that either star hosts an alien megastructure. Universe Today noted that ordinary astrophysical explanations, including an unresolved binary companion or low metallicity, may account for the unusually slow rotation.

Torlakcik proposes follow-up observations to test whether this kind of search can be narrowed in the future. For now, the work adds another possible target pattern to technosignature searches: stars rotating far more slowly than comparable stars.

This story draws on original reporting from Phys.org.