The quest for extraterrestrial life has fascinated scientists, philosophers, and enthusiasts for centuries. In the modern era, this curiosity has evolved into the Search for Extraterrestrial Intelligence (SETI), a scientific endeavor that seeks to detect signs of technologically advanced civilizations beyond Earth. Over the past six decades, SETI researchers have focused primarily on searching for radio signals from distant civilizations, but the scope of SETI research has expanded considerably. Researchers now explore other potential indicators of extraterrestrial activity, such as directed energy, neutrinos, gravitational waves, and even the detection of megastructures. These efforts aim to identify “technosignatures”—evidence of technology used by extraterrestrial civilizations.
While the search for radio signals remains a cornerstone of SETI, the study of megastructures like Dyson spheres, Clarke bands, and Niven rings has gained prominence. These hypothetical structures could be built by advanced civilizations to harness the energy of their star or perhaps serve other purposes. The ongoing research into these phenomena has led to exciting developments, including the work of Project Hephaistos, Sweden’s first SETI initiative. This project aims to explore a broad spectrum of potential technosignatures beyond radio signals, expanding our understanding of what extraterrestrial technology might look like.
Project Hephaistos: Sweden’s Bold SETI Initiative
Project Hephaistos, named after the Greek god of blacksmiths and craftsmen, marks a significant step in the evolving field of SETI. This project, led by Professor Erik Zackrisson and his team, focuses on the search for technosignatures in general, rather than limiting the search to deliberate signals sent from distant civilizations. One of the most exciting aspects of Project Hephaistos is its exploration of Dyson spheres—enormous, energy-harvesting structures that could potentially be built around stars by advanced civilizations to capture their energy output.
A Dyson sphere is an idea first proposed by the British-American physicist Freeman Dyson in 1960. Dyson suggested that a sufficiently advanced civilization might construct a structure capable of enclosing a star, capturing its energy, and providing power for its inhabitants. These theoretical megastructures would have a profound effect on the observed energy output of a star, potentially detectable from Earth. As a result, Dyson spheres have become a key area of focus in the search for extraterrestrial intelligence.
Project Hephaistos has already made significant strides in identifying Dyson sphere candidates. The project has produced a series of papers that explore various star systems to identify potential megastructures, using data from cutting-edge astronomical instruments like the Gaia Observatory. In a recent study published in the Monthly Notices of the Royal Astronomical Society: Letters, a team led by Tongtian Ren, a Ph.D. student at the Jodrell Bank Centre for Astrophysics at the University of Manchester, examined some of the stars identified by Project Hephaistos as potential Dyson sphere candidates. Their findings raised intriguing questions about the nature of these candidates and whether natural phenomena might explain some of the anomalies observed.
The Dyson Sphere Hypothesis and Technosignatures
The concept of a Dyson sphere arises from the assumption that advanced civilizations would require immense amounts of energy to sustain their technological needs. Harnessing the energy of an entire star would provide a virtually limitless power source, making such megastructures ideal candidates for detection by SETI researchers. These hypothetical structures could potentially radiate excess heat in the form of infrared radiation, detectable by telescopes here on Earth.
In their study, Ren and his team focused on a group of seven potential Dyson sphere candidates—designated A to G—discovered around M-type stars by the European Space Agency’s Gaia Observatory. These stars were selected from a vast sample of approximately 5 million stars cataloged by Gaia, a mission launched in 2013 to survey the stars in our galaxy. Using this data, Project Hephaistos identified stars that exhibited infrared excess, a characteristic often associated with Dyson spheres. However, as Ren and his team analyzed the data, they found that some of these candidates could have alternative, natural explanations.
Previously, Ren and his team had suggested that dust-rich debris disks—structures formed by the collision of asteroids or comets—could create the observed infrared excess. These debris disks absorb light from their stars and re-emit it as infrared radiation, which could mimic the signals expected from Dyson spheres. However, their latest findings suggested that some of the radio emissions associated with these candidates were more likely to originate from background sources, rather than from the stars themselves. This insight was crucial in refining the search for true Dyson spheres.
The Role of Active Galactic Nuclei (AGN)
One of the most significant findings of Ren’s team was the identification of Active Galactic Nuclei (AGN) as a potential source of contamination. AGNs are extremely energetic regions found at the centers of some galaxies, typically containing supermassive black holes. These regions emit vast amounts of radiation across the electromagnetic spectrum, including radio waves and infrared radiation. AGNs are known to be faint in optical wavelengths but can be exceptionally bright in the infrared.
Ren and his team discovered that several of the potential Dyson sphere candidates in the Project Hephaistos catalog had counterparts in databases of known AGNs. The team hypothesized that the radio signals observed from these stars were likely contaminated by the radio emissions from AGNs located in the background, rather than originating from the stars themselves. This realization suggested that the initial observations of these candidates, which had been exciting for their potential to be Dyson spheres, might have been misinterpreted.
Professor Michael Garrett, Ren’s supervisor, explained the significance of this finding: “When I saw the original results from Project Hephaistos last year, I was skeptical. They had surveyed 5 million stars, and if you do that, there is a good chance your measurements might include emission from background sources. You don’t expect stars to show radio emission at this level, and it basically tells you that the radio emission is probably coming from background (radio) galaxies.”
The Discovery of Dust Obscured Galaxies (DOGs)
As the team delved deeper into the data, they found that the radio emissions from some of the potential Dyson sphere candidates shared key characteristics with dust-obscured galaxies (DOGs). DOGs are galaxies that are heavily obscured by dust, making them difficult to detect in optical wavelengths. However, they are often very bright in the infrared, making them prime candidates for contamination in searches for Dyson spheres.
The team considered the possibility that the observed signals from Project Hephaistos were not the result of an advanced extraterrestrial civilization, but rather a natural astrophysical phenomenon: hot DOGs. These galaxies, while faint in optical wavelengths, emit intense radiation in the infrared and can produce significant radio emissions, leading to a potential misinterpretation of the data as Dyson spheres.
The Next Steps in the Search for Dyson Spheres
Although Ren and his team’s analysis suggested that some of the candidates identified by Project Hephaistos were contaminated by radio emissions from AGNs or DOGs, they cautioned against dismissing the entire catalog of potential Dyson sphere candidates. While some of the candidates were likely misidentified, there remained the possibility that others might still be genuine megastructures, requiring further investigation.
The team’s findings underscore the importance of multiwavelength observations when searching for technosignatures. By combining data from various parts of the electromagnetic spectrum, astronomers can more accurately distinguish between natural astrophysical phenomena and artificial structures. The team used data from advanced radio observatories like the e-MERLIN and the European VLBI Network (EVN) to conduct high-resolution observations, allowing them to more clearly identify the source of the emissions.
As Garrett emphasized, the work of Project Hephaistos represents just the beginning of a much larger and more complex search: “We don’t know that all of the candidates are contaminated, but some, maybe all, probably are. I really hope some of them are indeed good Dyson sphere candidates. This all shows that a multiwavelength approach is really required when looking for candidates in order to rule out background contamination.”
The Future of SETI and Dyson Sphere Research
The search for Dyson spheres and other technosignatures remains a challenging and uncertain endeavor. The tools required to detect such structures—whether they are vast megastructures or traces of advanced technologies—are still in development. Instruments like the Gaia Observatory and the Wide-field Infrared Survey Explorer (WISE) have provided crucial insights into potential Dyson sphere candidates, but they have limitations, and the next generation of space telescopes may take decades to come online.
As Tongtian Ren noted, the rapid pace of consumer electronics does not match the slow development cycles of astronomical instruments. “Gaia and WISE provided a crucial observational window. The next generation of similar probes may not be available for a long time, making it unlikely that a large-scale Dyson sphere search program like Project Hephaistos will be conducted again in the near future.”
Despite these challenges, the findings from Ren and his colleagues are a significant step forward in the ongoing search for extraterrestrial intelligence. By refining our methods for detecting technosignatures and carefully considering all possibilities—both natural and artificial—we continue to edge closer to answering one of humanity’s most profound questions: Are we alone in the universe?
In conclusion, the search for Dyson spheres and other technosignatures is a fascinating and evolving area of SETI research. While current data suggests that some of the promising candidates identified by Project Hephaistos may be contaminated by natural phenomena like AGNs and DOGs, the search continues. Each new discovery brings us one step closer to understanding the nature of advanced extraterrestrial civilizations and the potential for life beyond Earth.
Reference: T Ren et al, High-resolution imaging of the radio source associated with Project Hephaistos Dyson Sphere Candidate G, Monthly Notices of the Royal Astronomical Society: Letters (2025). DOI: 10.1093/mnrasl/slaf006