The latest Swedish-led search for technosignatures in the form of Dyson spheres has again come up empty-handed. The two latest stellar candidates in the hunt for such hypothetical extraterrestrial technology have been eliminated as Dyson spheres.
Project Hephaistos, a Uppsala University-led initiative, used NASA’s James Webb Space Telescope to observe two new Dyson sphere candidates. The Webb telescope obtained images and spectra of two M-dwarf stars, as noted in two papers submitted to the journal Monthly Notices of the Royal Astronomical Society (MNRAS). The work is currently published on the arXiv preprint server.
Dyson spheres are hypothetical megastructures constructed around stars to harvest radiation energy, possibly for the purpose of powering habitats, vessel propulsion, computing or transmitting long-range signals, the MNRAS authors note. The primary technosignature of such structures is the waste heat emitted, usually assumed to be detectable as excess radiation in the infrared, they write.
Most such putative waste heat emissions would show up in the mid-infrared spectrum.
“We find that the infrared excess does not originate from Dysonian megastructures, or other radiation mechanisms close to these stars, but from background galaxies projected to be within an arcsec of the M dwarfs,” the MNRAS papers’ authors write. One has a mid-infrared spectrum consistent with being a Hot Dust Obscured Galaxy (Hot DOG), they note.
The other galaxy has what the authors call an extended morphology with bright knots and a spectrum consistent with a dusty starburst, they note.
These latest results point out the extreme difficulty of looking for technosignatures of any sort, whether from highly advanced Kardashev III- or IV-type civilizations capable of harnessing whole galaxies or a Kardashev I- or II-type civilization capable of harnessing the energy of a single star.
“This is a follow-up with the Webb telescope to observe two stars that we identified in a survey of some 1 million stars within about 1,000 light-years of Earth,” Andreas Korn, a senior lecturer in astrophysics at Uppsala University in Sweden and a member of the Project Hephaistos team, told me in Stockholm.
That survey was first conducted with the European Space Agency’s Gaia satellite and NASA’s WISE (Wide-field Infrared Survey Explorer) mission. The aim was to look for stars that have surprisingly low fluxes in the optical and surprisingly high fluxes in the infrared.
As Korn notes, such a combination is seen as a potential technological signature of an extraterrestrial civilization, referred to in general terms as a Dyson sphere.
The two stars that were initially the most promising were relatively faint M-dwarf stars, around 15th magnitude and estimated to be a few billion years old.
“Nothing that you can observe with the naked eye,” Korn says.
“Eventually, even if you are using this Dyson sphere energy to do computing, the energy will be transformed and emitted in the infrared as waste heat,” Korn says. “But this is the signature that we were looking for: a star that is a little bit too faint in the optical and has substantial amounts of waste heat in the infrared.”
But what they found was a superposition of run-of-the-mill M dwarfs and two background galaxies.
“WISE gives us just a coarse image, and that’s why the photons from the background galaxy and the M dwarfs were blended together so we couldn’t tell them apart,” Korn says. “But with Webb, we can tell the two apart and conduct separate analyses of either the galaxy or the foreground M dwarf.”
What’s next?
The most immediate problem in any future search is that, as the authors note, a substantial fraction of the Project Hephaistos Dyson sphere candidates appears to be contaminated by background galaxies. But proposed mid-infrared telescopes in the 2030s could provide higher-resolution data over wide areas, the authors write.
“So, there will be infrared surveys with better spatial resolution coming online in the 2030s that may eventually solve that problem,” Korn says.
As for the handiwork of civilizations capable of modifying whole galaxies?
On a galactic scale, astronomers would look for objects that are fainter than expected in a manner that can’t be explained by known, completely natural astrophysics.
The idea of Dyson spheres around main-sequence stars remains an intriguing concept. But would a planetary system even have enough raw material to build such monstrosities?
A Dyson swarm
“You don’t have to build a solid structure; a Dyson swarm of satellites could fulfill the same purpose,” Korn says. “It would collect less energy than a solid sphere, but it could still collect more energy than is available on a planetary scale.”
If such hypothetical Dyson satellites were orbiting the star in a manner that would be detectable, this would lead to some variability in the target star’s luminosity.
The bottom line?
“There are many sources of variability in the physical world, but if you see that there was a periodicity in the variability, then you could potentially constrain the morphology of an artificial megastructure,” Korn says.
Publication details
Andreas J. Korn et al, Project Hephaistos — III. Characterizing anomalous infrared sources identified as Dyson-sphere candidates, arXiv (2026). DOI: 10.48550/arxiv.2607.25701
Erik Zackrisson et al, Project Hephaistos — IV. James Webb Space Telescope Observations of Two Dyson Sphere Candidates, arXiv (2026). DOI: 10.48550/arxiv.2607.09460
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NASA’s Webb telescope rules out two new Dyson sphere candidates (2026, August 27)
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