There is something poetic about humanity’s attempt to discover other civilizations somewhere in the expanse of the Milky Way. There is also something nonsensical about it. But we won’t stop. There is no doubt about it.
One group of scientists thinks we may already have detected technosignatures from the Dyson spheres of a technological civilization, but the detection is hidden in our vast amounts of astronomical data.
The Dyson Sphere is a hypothetical engineering project that only highly advanced civilizations could build. In this sense, “advance” means the kind of almost unimaginable technological power that would allow a civilization to build a structure around an entire star. These Dyson spheres would allow a civilization to harness all the energy of a star.
A civilization can only build something so massive and complex if it has reached level II on the Kardashev scale. Dyson Spheres can be a technosignature, and a team of researchers from Sweden, India, the UK and the US have developed a way to search for the Dyson Sphere technosignature, which they call Project Hephaistos. (Hephaestus is the Greek god of fire and metallurgy.)
They publish their results in the Monthly Notices of the Royal Academy of Sciences. The study is entitled “Project Hephaestus – II. Dyson Sphere Candidates from Gaia DR3, 2MASS and WISE.” Lead author Matthias Suazo is a PhD student in the Department of Physics and Astronomy at Uppsala University in Sweden. This is the second document introducing the Hephaistos project. The first one is here.
“In this study, we present a comprehensive search for partial Dyson spheres by analyzing optical and
infrared observations from Gaia, 2MASS and WISE,” the authors write. These are large-scale astronomical studies designed for various purposes. Each of them generates a huge amount of data from individual stars. “This second paper examines Gaia DR3, 2MASS and WISE photometry of ~5 million sources to build a catalog of potential Dyson spheres,” they explain.
Combing through all this data is a difficult task. In this work, the team of researchers developed a special data pipeline to work its way through the combined data from the three studies. They indicate that they are looking for partially completed spheres that would emit excess infrared radiation. “This structure will emit waste heat in the form of mid-infrared radiation, which in addition to the level of completion of the structure will depend on its effective temperature,” Suazo and colleagues write.
The problem is, they’re not the only objects that do this. Many natural objects do as well, such as circumstellar dust rings and nebulae. Background galaxies can also emit excess infrared radiation and create false positives. The pipeline’s job is to filter them out. “A dedicated pipeline has been developed to identify potential candidates for Dyson spheres, focused on detecting sources that exhibit anomalous infrared excesses that cannot be attributed to any known natural source of such radiation,” the researchers explain.
This block diagram shows what the pipeline looks like.
The pipeline is just the first step. The team is subjecting the list of candidates to further investigation based on factors such as H-alpha emission, optical variability and astrometry.
368 sources survived the final cut. Of these, 328 were rejected as blends, 29 were rejected as irregular, and 4 were rejected as nebulae. This left only 7 potential Dyson spheres out of about 5 million initial objects, and the researchers are confident that these 7 are legitimate. “All sources are clear mid-infrared emitters with no obvious contaminants or signatures that indicate an obvious mid-infrared origin,” they explain.
These are the seven strongest candidates, but researchers know they’re still only candidates. There may be other reasons why the seven emits excess infrared. “The presence of warm debris disks around our candidates remains a plausible explanation for the infrared excess of our sources,” they explain.
But their candidates appear to be M-type stars (red dwarfs), and debris disks around M-dwarfs are very rare. However, this gets complicated because some research suggests that the debris disks around M-dwarfs form differently and behave differently. One type of debris disk, called Extreme Debris Disks (EDD), may explain some of the brightness the team sees around its candidates. “But these sources have never been observed in association with M dwarfs,” Suazo and his co-authors write.
This leaves the team with three questions: “Are our candidates weird young stars whose flux doesn’t change over time? Are the M-dwarfs of these stars of extreme partial luminosity? Or something completely different?”
“After analyzing the optical/NIR/MIR photometry of ~5 x 106 sources, we found 7 apparent M dwarfs showing an infrared excess of unclear nature that is consistent with our Dyson sphere models,” the researchers wrote in their conclusion. There are natural explanations for the excess infrared light coming from these 7, “But none of them clearly explain such a phenomenon in the candidates, especially given that they are all M dwarfs.”
The researchers say that follow-up optical spectroscopy will help to better understand these 7 sources. A better understanding of H-alpha emission is particularly valuable, as it can also come from young discs. “In particular, analyzing the spectral region around H-alpha may help us eventually discard or verify the presence of young discs,” the researchers wrote.
“Further analyzes are definitely needed to reveal the true nature of these sources,” they conclude.
