NASA's Webb Telescope Rules Out Two New Dyson Sphere Candidates
The search for signs of advanced extraterrestrial intelligence took another careful step forward — and then paused — as the latest findings from Project Hephaistos, a Swedish-led technosignature initiative, confirmed that two promising stellar candidates are not, in fact, harboring alien megastructures. Instead, they are the victims of a cosmic optical illusion: background galaxies masquerading as infrared-bright stars. While disappointing to those hoping for a breakthrough, the results underscore both the ingenuity of modern observational astronomy and the profound difficulty of searching for technological signatures across interstellar distances.
What Are Dyson Spheres — and Why Are Scientists Looking for Them?
Dyson Spheres are hypothetical megastructures, first theorized by physicist and mathematician Freeman Dyson in his landmark 1960 paper published in Science, designed to entirely or partially encapsulate a star in order to harvest its radiated energy. The concept emerged as a logical extrapolation of humanity's growing energy consumption: if a sufficiently advanced civilization requires energy on a truly astronomical scale, the most efficient solution might be to construct a vast shell or swarm of collectors around their host star.
As described in two papers recently submitted to the journal Monthly Notices of the Royal Astronomical Society (MNRAS), Dyson Spheres could theoretically power everything from planetary habitats and interstellar propulsion systems to continent-sized computing arrays or powerful long-range communication beacons. Such structures represent the aspirations of what scientists classify as a Kardashev Type II civilization — one capable of harnessing the total energy output of an entire star.
"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. 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." — Andreas Korn, Uppsala University
The key observable signature of such a structure would be thermodynamic waste heat. No energy conversion process is perfectly efficient, and any civilization using a stellar-scale energy collector would inevitably radiate excess heat — most likely detectable as an anomalous excess of mid-infrared radiation emanating from a star that appears curiously dim in visible light. This combination — optically faint yet infrared-bright — is the primary technosignature that Project Hephaistos has been systematically hunting.
Project Hephaistos: A Million-Star Survey
Project Hephaistos, led by researchers at Uppsala University in Sweden, represents one of the most ambitious and methodologically rigorous technosignature searches ever conducted. The project began with an enormous foundational survey of approximately one million stars located within roughly 1,000 light-years of Earth. This survey combined data from two powerful space observatories:
- ESA's Gaia satellite — which provided precise optical brightness measurements and stellar classifications across an unprecedented portion of the Milky Way.
- NASA's WISE (Wide-field Infrared Survey Explorer) — which contributed wide-area infrared photometry, revealing stars with anomalously high infrared flux relative to their optical brightness.
By cross-referencing these datasets, the team identified a subset of stellar candidates whose energy profiles deviated from what natural astrophysical processes alone could explain — stars that appeared to be radiating far more thermal energy than their optical luminosities would predict. These were flagged as candidate Dyson Sphere hosts for follow-up investigation.
Andreas Korn, a senior lecturer in astrophysics at Uppsala University and a key Project Hephaistos team member, described the selection process during a conversation in Stockholm: "This is follow-up with the Webb telescope to observe two stars that we identified in a survey of some one million stars within about 1,000 light years of Earth."
The two stars ultimately selected for Webb follow-up were relatively faint M-dwarf stars of approximately 15th magnitude — well beyond naked-eye visibility — estimated to be several billion years old. M-dwarfs, the most common type of star in the Milky Way, are themselves compelling hosts for technosignature searches, as their long lifetimes theoretically allow billions of years for civilizations to develop and potentially construct megastructures. Learn more about ongoing technosignature research at the SETI Institute.
Webb's Revelation: Background Galaxy Contamination
When NASA's James Webb Space Telescope (JWST) — the most powerful space observatory ever deployed — turned its golden mirrors toward these two stellar candidates, it delivered a decisive and illuminating answer, even if not the one researchers had hoped for. The extraordinary angular resolution and infrared sensitivity of Webb allowed astronomers to resolve what WISE had blended into a single, seemingly anomalous source.
As the MNRAS papers' authors conclude: "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."
In each case, a distant background galaxy happened to align almost precisely with the foreground M-dwarf star along our line of sight — a chance superposition that WISE's relatively coarse spatial resolution could not disentangle. Webb's dramatically superior resolution cut through this ambiguity:
- One of the background contaminants has a mid-infrared spectrum consistent with a Hot Dust Obscured Galaxy (Hot DOG) — an extremely luminous, dust-enshrouded galaxy type known for intense mid-infrared emission driven by powerful hidden quasars or starbursts.
- The second background source exhibits an extended morphology with bright knots and a spectrum consistent with a dusty starburst galaxy — a galaxy undergoing a rapid, intense episode of star formation that generates enormous quantities of heated dust and infrared radiation.
"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. But with the Webb, we can tell the two apart and do separate analyses, either from the galaxy or from the foreground M dwarf." — Andreas Korn, Uppsala University
This finding carries a sobering implication for the broader project: as the MNRAS papers' authors note, "a substantial fraction of the Project Hephaistos Dyson Sphere candidates appears to be contaminated by background galaxies." This is a systematic challenge that will need to be addressed methodologically in future searches. You can explore JWST's full science capabilities at the NASA James Webb Space Telescope page.
The Kardashev Scale: Framing the Search for Mega-Civilizations
To appreciate the full scope of what Project Hephaistos is searching for, it helps to understand the Kardashev Scale — a classification system proposed by Soviet astronomer Nikolai Kardashev in 1964 to categorize civilizations by their total energy consumption:
- Kardashev Type I: A civilization that harnesses all available energy on its home planet — roughly 1016 to 1017 watts. Humanity currently sits just below this threshold.
- Kardashev Type II: A civilization that captures the full energy output of its host star — approximately 4 × 1026 watts. A Dyson Sphere around a Sun-like star would enable this level of energy use.
- Kardashev Type III: A civilization commanding the energy resources of an entire galaxy — roughly 1037 watts — potentially through networks of stellar megastructures or even galactic-scale engineering.
- Kardashev Type IV (extended scale): A hypothetical civilization capable of harnessing energy at a universal scale, a concept that stretches the imagination but provides a framework for galactic-scale technosignature searches.
These latest results highlight the extreme difficulty of detecting technosignatures at any point on this scale, whether from the relatively modest engineering of a Kardashev I or II civilization or the mind-bending galactic modifications of a Type III or IV civilization. On a galactic scale, astronomers would search for objects that are unexpectedly and inexplicably fainter than known astrophysical models predict — a galaxy-wide Dyson network might cause its host galaxy to appear anomalously dim in visible light while blazing in the infrared.
Beyond the Solid Sphere: The Dyson Swarm
A common misconception about Dyson Spheres is that they must be rigid, monolithic shells completely encasing a star. In reality, the engineering challenges of constructing a solid sphere around a star are almost incomprehensibly vast — the material requirements alone would dwarf anything our solar system could provide. Korn addresses this directly:
"You don't have to build a solid structure; a Dyson swarm of satellites could fulfill the same purpose. It would collect less energy than a solid sphere, but it could still collect more energy than available on a planetary scale." — Andreas Korn, Uppsala University
A Dyson Swarm — a vast, distributed network of individual solar collectors or habitats orbiting a star in coordinated patterns — is considered far more physically plausible than a solid shell, and it may actually produce more distinctive and detectable observational signatures. As each element of the swarm transits the face of the host star, it would produce characteristic periodic dips in the star's optical brightness, analogous to the transit signals used to detect exoplanets but with potentially unique light-curve shapes reflecting the artificial, geometric nature of the structures.
As Korn explains: "There are many sources of variability in the physical world, but if you see that there was a periodicity to the variability, then you could potentially constrain the morphology of an artificial megastructure." This opens an entirely complementary avenue of technosignature search — one based on precise stellar photometry and time-domain astronomy rather than pure infrared excess detection.
The Path Forward: Next-Generation Infrared Observatories
While the current results are negative, they are scientifically valuable — they validate the methodology, identify its primary limitation (background galaxy contamination), and point toward the tools needed to overcome it. The key bottleneck today is spatial resolution at mid-infrared wavelengths across wide survey areas. WISE, which enabled the initial candidate selection, lacks the angular resolution to separate faint background galaxies from nearby M-dwarf stars. JWST provides the resolution but is optimized for deep, targeted observations rather than wide-field surveys.
The scientific community is looking toward the next generation of space-based mid-infrared observatories, potentially coming online in the 2030s, to provide the transformative combination of high angular resolution and broad sky coverage needed to systematically clear the candidate list of contamination and pursue genuine anomalies with confidence. Initiatives such as the proposed ESA space science missions and future NASA concepts may provide this capability.
As Korn notes with measured optimism: "There will be infrared surveys that have better spatial resolution coming online in the 2030s that may eventually solve that problem."
In the meantime, the growing field of technosignature science continues to mature, with researchers developing more sophisticated statistical frameworks, multi-wavelength analysis techniques, and time-domain search strategies. The NASA Technosignatures program has increasingly recognized this field as a legitimate scientific pursuit worthy of dedicated funding and observational resources.
The Bigger Picture: Why This Search Matters
It is easy to view repeated null results as discouraging, but scientists caution against this interpretation. Each confirmed non-detection provides statistically meaningful constraints on the prevalence of detectable technostructures in the solar neighborhood. The fact that a survey of one million nearby stars has not yet yielded a confirmed Dyson Sphere candidate tells us something real — and potentially profound — about the distribution and nature of technological life in the galaxy.
Moreover, the cross-disciplinary benefits are substantial. The techniques developed for technosignature searches — precise infrared photometry, multi-wavelength cross-matching, time-domain variability analysis, and high-resolution follow-up spectroscopy — have direct applications in exoplanet science, stellar astrophysics, and extragalactic astronomy. The discovery of two previously uncharacterized background galaxies, including a rare Hot Dust Obscured Galaxy, is itself a scientifically valuable byproduct of this search. Further reading on the broader search for life can be found at the HubbleSite.
The universe remains silent on the question of Dyson Spheres — for now. But with each generation of more powerful telescopes and more sophisticated search strategies, humanity draws a slightly clearer map of what is out there, and what, perhaps, is waiting to be found.
Key Takeaways
- Project Hephaistos, led by Uppsala University, conducted a technosignature survey of ~1 million stars within 1,000 light-years using ESA's Gaia and NASA's WISE satellites.
- Two M-dwarf candidates flagged for anomalous infrared excess were followed up with NASA's James Webb Space Telescope.
- Webb's superior resolution revealed that the infrared excess originated from background galaxies — not Dyson Spheres — superimposed along the same line of sight.
- One background source is consistent with a Hot Dust Obscured Galaxy (Hot DOG); the other is consistent with a dusty starburst galaxy.
- A significant fraction of Project Hephaistos candidates may be affected by similar background galaxy contamination, highlighting the need for higher-resolution mid-infrared surveys.
- Future mid-infrared space telescopes planned for the 2030s could provide the angular resolution and sky coverage needed to overcome this limitation.
- Alternative detection strategies, including searching for periodic stellar variability caused by transiting Dyson Swarm elements, offer complementary pathways to discovery.
