Some of the coldest objects currently listed as stars in the Milky Way may not be stars at all. A new study by astrophysicist Amirnezam Amiri from the University of Arkansas suggests that these extremely cold objects could instead be giant energy-harvesting structures built by advanced alien civilisations. According to the research, these objects match the expected behaviour of engineered systems that collect a star’s energy and release the leftover heat as infrared radiation.The study is set to be published in the journal Universe and it offers a new mathematical method to search for these possible alien structures. The idea was first proposed by physicist Freeman Dyson in 1960. Instead of a single giant shell surrounding a star, modern scientists now favour the idea of a ‘Dyson swarm‘, made up of millions of separate solar collectors orbiting the star. Researchers believe this design is far more practical than a solid sphere, which would be nearly impossible to build.According to Amiri’s study, red dwarfs and white dwarfs would be the best stars for an advanced alien civilisation to build such a system around.
Red dwarfs and White dwarfs could be the best choice
Red dwarfs are the most common stars in the Milky Way. They burn their nuclear fuel very slowly, allowing them to remain stable for trillions of years. This gives any advanced civilisation plenty of time to build and maintain a large energy-collecting system. Because red dwarfs are much smaller than stars like the Sun, they also require far fewer materials to surround.
A Red dwarf star and a White dwarf star
Amiri wrote that “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 could be even better. These are the dense remains of Sun-like stars after they have reached the end of their lives. Although they shrink to only about one per cent of their original size, they continue giving off energy for billions of years. Since they are so small, a Dyson swarm could orbit just a few million kilometres above the surface, reducing the amount of material needed to collect the star’s energy.
Looking for an unusual heat signature
A Dyson swarm would completely change the way a star appears on a Hertzsprung-Russell (H-R) diagram, which astronomers use to compare a star’s temperature with its brightness.The idea is simple. A Dyson swarm would absorb most of the visible light from its star, use that energy to power an advanced civilisation, and then release the unused energy as infrared heat. The total amount of energy would stay the same, but much less would be seen as visible light.
Hertzsprung-Russell Diagram to Study the Evolutionary Stages of Stars
As a result, the object would shine brightly in infrared light while appearing unusually dim in visible light. On an H-R diagram, it would move to the coldest part of the chart even though its overall energy output would remain unchanged.This creates a very unusual signature. A normal red dwarf has a surface temperature of about 3,000 Kelvin, while a fully developed Dyson swarm could reduce the object’s apparent temperature to around 50 Kelvin. That would make it colder than any naturally occurring star and place it in an empty part of the H-R diagram where astronomers would expect to find possible signs of alien technology.
What scientists are looking for
Amiri’s research also explains how scientists could tell the difference between a Dyson swarm and a natural cloud of dust.Young stars and dying stars are often surrounded by thick disks of dust, which also glow in infrared light. However, these dust clouds leave behind clear chemical signatures, including emissions from silicate minerals.A Dyson swarm would look very different. Instead of dusty material, it would produce a much cleaner infrared spectrum because it would be made of organised structures rather than natural debris.The gaps between millions of orbiting solar collectors would also create another clue. As the collectors move around the star, they would block different amounts of light at different times, causing irregular changes in brightness. These patterns would be very different from the regular changes seen in naturally variable stars.
How a hypothetical Dyson Swarm system would look like
Astronomers are already searching for these exact signs. The James Webb Space Telescope, with its powerful infrared instruments, is one of the main tools being used. At the same time, projects such as Project Hephaistos are analysing millions of older observations from missions including the Wide-field Infrared Survey Explorer (WISE).In May 2024, Project Hephaistos identified seven possible Dyson sphere candidates from a survey of about five million stars, all centred on red dwarfs. One candidate was later ruled out after researchers found that a distant supermassive black hole happened to line up behind the star. That leaves five candidates still being studied.Amiri’s new model gives astronomers a clearer way to test these objects and determine whether they are simply unusual natural systems or possible signs of advanced alien technology.
