🇺🇸▼
Since physicist Freeman Dyson first proposed the idea in 1960, the concept of the "Dyson sphere" has become a primary target for astronomers searching for signs of advanced technology. A highly advanced civilization might build a vast structure, or more likely a swarm of individual components, around their star to capture its total energy output. While the theory is possible, a key question remains: what would such a megastructure actually look like when viewed from Earth? A new study, soon to be published in the journal Universe by Amirnezam Amiri of the University of Arkansas, investigates this specific question. The research also identifies which types of stars are the most promising locations to search for these hypothetical constructs.
Perhaps unsurprisingly, one prime candidate for these searches is the red dwarf. These stars are the most common in the Milky Way galaxy. They consume their nuclear fuel very slowly, resulting in extraordinarily long lifespans that could last for trillions of years. This longevity, combined with their relatively small size compared to our Sun, makes them particularly attractive targets. A Dyson swarm could orbit a red dwarf at a distance of just 0.05 to 0.3 astronomical units from its surface. This relatively close orbit would significantly reduce the amount of material required for construction.
White dwarfs represent an even more efficient option in terms of material cost. These objects are the compact, dense remnants of stars like our Sun, having collapsed down to a radius that is only about 1% of their original size. This extreme compactness allows a Dyson swarm to be constructed just a few million kilometers from the star's surface. This distance significantly reduces the engineering challenges of encircling a much larger star. Furthermore, white dwarfs emit a steady stream of energy for billions of years, acting as a reliable and long-lasting power source for any civilization that harnesses them.
But what observable signature would a star surrounded by a Dyson swarm produce? Astronomers typically use the Hertzsprung-Russell diagram to classify stars based on two key properties: temperature and luminosity. A Dyson sphere would fundamentally alter a star's position on this diagram. Since it would block essentially all of the star's visible light, it would no longer appear as a normal star. However, the fundamental law of conservation of energy still applies: the total energy emitted by the structure must equal the total energy it receives from the star it encloses.
Consequently, the sphere must radiate the same total energy back into space. This energy is not emitted as visible light, however, but as waste heat in the form of infrared radiation. Conceptually, a Dyson sphere is a shell that absorbs a star's light, uses the energy for the civilization's needs, and then re-emits the byproduct as infrared light. This process would shift the object's apparent location entirely to the far right on the H-R diagram, the region representing very low temperatures.
The object's total luminosity, or brightness across all wavelengths of light known as bolometric luminosity, would remain unchanged. Therefore, on the H-R diagram, it would maintain the same vertical position as its host star, whether it is a red dwarf or a white dwarf. The dramatic change is its horizontal position. For example, a typical red dwarf, already located in the cool, lower-right corner of the diagram, has a surface temperature around 3,000 Kelvin. A Dyson sphere surrounding any star, by contrast, would have a much lower equilibrium temperature, potentially as low as 50 Kelvin. This is two orders of magnitude cooler. No known natural stars exist in this extremely cold region of the diagram, making any object detected there a compelling candidate for an artificial megastructure.
Another factor supporting the identification of a Dyson swarm is a notable absence: a lack of dust. Stars are often surrounded by circumstellar disks containing silicate dust particles, which produce specific spectral emission lines. A functioning Dyson swarm's radiator panels, however, would likely be free of such dust. To a spectrograph, the object would therefore appear remarkably "clean," lacking the typical dusty signatures that astronomers usually expect.
One critical nuance is that a realistic Dyson "swarm" would not be a solid, continuous shell. It would consist of a vast collection of individual orbiting collectors, likely with significant gaps between them or varying thicknesses. This design is necessary to make the material requirements physically plausible; modern calculations show that building a rigid, complete sphere is impossible. If gaps exist, the star's light would occasionally and irregularly peek through as the swarm rotates. This would produce a highly unusual, non-natural pattern of brightness variation, known as a light curve, which could itself be a detectable signature.
Infrared astronomy is perfectly suited to the search for these cool megastructures. The James Webb Space Telescope, with its advanced infrared capabilities, is ideally positioned to monitor for such signatures. Even older space telescopes, like the Wide-field Infrared Survey Explorer, are actively used in this search. In May 2024, Project Hephaistos, a dedicated search for Dyson spheres, published results from scanning a catalog of five million stars. The project identified seven strong candidate objects, all around red dwarf stars.
One candidate was later ruled out because its anomalous infrared signal was explained by a supermassive black hole perfectly aligned behind it. This left five promising candidates that merit closer observation. The new theoretical framework provided by Amiri's paper adds a powerful tool to this ongoing search. By clarifying how Dyson spheres would appear on the fundamental H-R diagram used by all astronomers, it refines our understanding of what to look for in the vast dataset of the sky. This work brings science one step closer to potentially identifying one of the most elusive targets in astronomy: a definitive technosignature from an advanced civilization.