New SETI approach looks for dyson spheres based on what they could be used for

In 1960, the renowned physicist Freeman Dyson published a groundbreaking paper titled “Search for Artificial Stellar Sources of Infrared Radiation.” In this paper, he proposed the intriguing concept of “Dyson spheres,” megastructures that advanced extraterrestrial civilizations could potentially build around their parent stars. These structures, he suggested, might be detectable through the “waste heat” they emit in the mid-infrared spectrum, which remains a valuable technosignature in the Search for Extraterrestrial Intelligence (SETI).

Despite extensive efforts to detect Dyson spheres and similar constructs based on their heat signatures, these searches have yielded no conclusive results. This has led some scientists to suggest refining the search parameters. In a recent preprint paper on arXiv, Jason T. Wright, an astronomy and astrophysics professor affiliated with the Center for Exoplanets and Habitable Worlds and the Penn State Extraterrestrial Intelligence Center (PSTI), proposes a novel approach. He recommends that SETI researchers shift their focus towards detecting indications of activity within these structures rather than relying solely on heat signatures.

Wright’s study centers around the Landsberg limit, a fundamental concept in thermodynamics that defines the maximum efficiency for harvesting solar radiation. This limit is crucial because Dyson’s original proposal was rooted in the idea that all life, including technologically advanced civilizations, seeks to exploit free energy gradients, akin to photosynthetic organisms using sunlight for oxygen and nutrients production. However, there is an absolute limit to how much energy a star can release in various forms, including visible light, infrared, and ultraviolet radiation.

Dyson reasoned that some of this energy would inevitably be expelled from the Dyson structure as waste heat. By leveraging advances in infrared astronomy, astronomers could theoretically measure the energy consumption of an advanced civilization by detecting this heat emission. Thus far, only three comprehensive all-sky mid-infrared surveys have been conducted, which include the Infrared Astronomical Satellite (IRAS), Wide-field Infrared Survey Explorer (WISE), and AKARI.

Traditionally, astronomers have searched for infrared emissions from stars, primarily to identify warm orbital material around them. If a star doesn’t typically have orbiting material, scientists can investigate further to determine if any observed material resembles dust or other substances. However, all previous search attempts have faced challenges due to the lack of a well-defined theory describing what the waste heat from a Dyson sphere would look like, given the unknown properties of the materials composing such a structure.

Various theoretical models have been proposed by astrophysicists, including Wright himself, to predict the thermal signatures of Dyson spheres. However, these models often rely on simplifications and assumptions, such as spherical symmetry, orbital distances from the star, while failing to accurately predict temperatures, radiative interactions, or optical properties of the materials involved. This leads to a critical consideration highlighted by Wright: understanding the purpose of the Dyson structure, or the “work” it performs, can provide insights into its material properties.

Freeman Dyson recognized that harnessing a star’s energy was just one potential purpose for constructing megastructures like Dyson spheres. Some SETI researchers have suggested these structures could serve as stellar engines, capable of moving stars (referred to as Shkadov thrusters), or as massive supercomputers known as Matrioshka brains. Matrioshka brains have a nested design, with inner layers absorbing direct sunlight and outer layers utilizing waste heat to optimize computational power.

Jason T. Wright delved into not only the physics but also the engineering aspects of building such megastructures. While Dyson primarily relied on the laws of physics to justify their existence, Wright considered the practical challenges. He proposed that civilizations might construct sections of a sphere gradually to expand their habitable space around a star. Taking this into account, Wright applied thermodynamics to Dyson spheres as computational devices and explored their observable consequences.

His findings suggested that there’s little advantage in creating nested shells and that the most efficient use of mass would involve smaller, hotter Dyson spheres. This challenges the expectation that Dyson spheres should be extremely large and cold for maximum efficiency. Wright suggested expanding the search parameters to include temperatures well above 300K (a bit hotter than Earth), as it’s more efficient to extract energy closer to the star, where it’s hotter.

These insights could guide future searches for Dyson structures, which are currently limited. One exception is the work of Mathias Suazo, a Ph.D. student in astrophysics at the University of Uppsala, and his colleagues at Project Hephaistos. They combined data from ESA’s Gaia Observatory, Two Micron All Sky Survey (2MASS), and NASA’s Wide-field Infrared Survey Explorer (WISE) to narrow down the search for thermal signatures indicating megastructures.

Their analysis identified approximately 5 million potential candidates within a volume spanning about 1,000 light-years in diameter. By creating a “best fit” model based on temperature and luminosity profiles and eliminating possible natural sources, Suazo and his team narrowed the list to 20 promising candidates. These sources are likely to undergo further observation using next-generation telescopes. Despite the absence of definitive evidence for megastructures so far, the possibility remains.

As Freeman Dyson once remarked regarding the motivations for such engineering feats, “My rule is, there is nothing so big nor so crazy that one out of a million technological societies may not feel itself driven to do, provided it is physically possible.” If even a few advanced civilizations in our galaxy have embarked on mega-engineering projects, we may eventually discover their traces.

Source: Universe Today

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