Astronomers have completed one of the most extensive searches ever conducted for unusual infrared emissions in our galactic neighborhood, analyzing approximately 5 million stars within 300 parsecs of Earth. The result has left researchers with seven candidates that defy conventional explanation.

The search, conducted as part of Project Hephaistos and published in May 2024 in the Monthly Notices of the Royal Astronomical Society, represents a 30-fold increase over previous similar surveys. Using data from the Gaia space telescope, the Two Micron All Sky Survey, and the Wide-field Infrared Survey Explorer, scientists at Uppsala University in Sweden developed an elaborate filtering system to identify stars emitting far more mid-infrared radiation than their visible light output would suggest.

What makes these seven final candidates particularly striking is not just their unusual infrared signatures, but the fact that they are all M-dwarf stars. These small, cool stars rarely harbor the warm debris discs or other natural phenomena that typically produce excess infrared radiation. The researchers applied increasingly stringent filters to their initial sample, rejecting sources that showed signs of youth, variability, nebular contamination, or instrumental artifacts. By the time the analysis concluded, just seven objects remained.

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The research team developed sophisticated models simulating how a star’s light output would change if surrounded by a heat-emitting structure. While the study was framed around searching for potential Dyson spheres, hypothetical megastructures proposed by physicist Freeman Dyson in 1960, the researchers acknowledge their findings represent unusual infrared sources that could have natural explanations not yet identified.

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The seven sources that survived this gauntlet of filters share remarkable properties. All are M-type dwarf stars with distances ranging from approximately 143 to 275 parsecs. Their Gaia G-band magnitudes fall between 15.99 and 18.39, placing them in the faint regime requiring sensitive detection. Most significantly, they all show low optical variability, with Gvar values between 0.90 and 1.03, and excellent astrometric solutions with RUWE values between 0.96 and 1.21.

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What makes these seven candidates particularly difficult to explain through conventional means is their status as M-dwarf stars. The occurrence of debris discs around M-dwarfs remains extremely rare in astronomical surveys. Only a handful of confirmed M-dwarf debris discs exist in the literature, and those typically show different characteristics than the candidates identified here.