While the concept has long been discussed in theory, an important question remains: if one actually existed, what would astronomers see? A new study by Amirnezam Amiri of the University of Arkansas, currently available as a pre-print on arXiv and scheduled for publication in Universe, explores exactly how these enormous structures might appear through modern telescopes. The research also identifies the types of stars most likely to host them.

Red Dwarfs and White Dwarfs Are Prime Targets

One of the strongest candidates is the red dwarf. These small, cool stars are the most common type in the Milky Way and consume their nuclear fuel so slowly that they can survive for trillions of years, far longer than the universe has existed so far.

Their relatively small size also makes them attractive from an engineering perspective. According to the study, a Dyson swarm could orbit a red dwarf at a distance of roughly 0.05 to 0.3 AU, requiring far less construction material than one built around a larger star like the Sun.

White dwarfs may be even more appealing. These dense stellar remnants are the leftover cores of Sun like stars that have exhausted their fuel and collapsed to only about 1% of their original size.

Because they are so compact, a Dyson swarm could orbit just a few million kilometers above the star's surface, dramatically reducing the scale of the structure needed. White dwarfs also release energy at a steady rate for billions of years, making them reliable long term power sources.

How a Dyson Sphere Would Change a Star's Appearance

Astronomers classify stars using the Hertzsprung-Russell (H-R) diagram, which plots stellar temperature against luminosity. A Dyson sphere would dramatically alter where a star appears on that chart.

Instead of allowing visible light to escape, the structure would absorb virtually all of the star's radiation. Since energy cannot simply disappear, the same amount of energy would have to be emitted back into space, but as heat in the infrared portion of the spectrum. In effect, the megastructure would absorb starlight, use that energy for whatever purpose its builders intended, and then radiate the excess as infrared heat.

Although the star's total energy output would remain unchanged, its apparent temperature would be much lower. Because H-R diagrams use bolometric luminosity (i.e. the luminosity over all of the spectra), the object would remain at the same luminosity but shift dramatically toward the cooler side of the diagram.

A Unique Infrared Signature

That temperature shift is one of the study's most striking predictions. A typical red dwarf has a surface temperature of about 3000K. A surrounding Dyson sphere, however, could have an effective temperature as low as 50K, around two orders of magnitude colder.

No known natural stars occupy that region of the H-R diagram. Any object found there would immediately become an intriguing candidate for further investigation.

Another possible clue would be the absence of dust. Ordinary stars often display silicate emission associated with dusty disks. A Dyson swarm, by contrast, would consist of radiator panels rather than dust, giving it an unusually "clean" spectrum.

Looking for Strange Light Curves

The study also emphasizes that a true solid Dyson sphere is almost certainly impossible to build. Modern calculations indicate that even around relatively small stars, the amount of material required would be unrealistic.

Instead, an advanced civilization would likely construct a swarm of many independent solar collectors, leaving gaps between them or varying their density throughout the structure. As those components orbited the star, they could produce highly unusual, non natural variations in brightness that would stand out from the behavior of ordinary stars.

James Webb and the Hunt for Alien Megastructures

The James Webb Space Telescope is especially well suited to search for these hypothetical structures because it specializes in infrared observations. Older missions such as WISE are also contributing to the effort.

In May 2024, researchers from Project Hephaistos reported seven promising Dyson sphere candidates, all associated with red dwarfs, after examining a catalog of roughly 5 million stars. One candidate was later ruled out because a perfectly aligned supermassive black hole in the background explained the unusual signal.

That still leaves five candidates deserving closer study. While none have been confirmed as alien megastructures, Amiri's work provides astronomers with another set of observational clues that could help distinguish genuine technosignatures from natural cosmic phenomena. If Dyson swarms do exist somewhere in the Milky Way, future infrared observations may finally reveal where they have been hiding.