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.

At first glance, such an extreme environment seems completely inhospitable. Daytime temperatures can reach roughly 1,000 to 2,000 Kelvin, while the night side is so cold that particle motion effectively stops. Yet new research suggests these worlds may not be as hostile to life as they appear.

“Just looking at the extreme temperatures on the day and night sides — like 1,000-2,000 Kelvin on the day side and absolute zero on the night side — might lead one to conclude these exoplanets are too harsh for life. But,” says Daisuke Noto, a postdoctoral researcher in Hugo Ulloa’s Penn GEFLOW Lab at the University of Pennsylvania, “life might find a way.”

In a study published in Nature Communications, Noto and collaborators from the Japan Agency for Marine-Earth Science and Technology and Hokkaido University found that “such exoplanets may be more tolerant of sustaining life as ‘tidal locking’ can contribute to maintaining moderate thermal environments locally by distributing heat flux laterally.”

Why Tidally Locked Exoplanets Are So Common

The findings challenge a common assumption about planets that always show the same face to their stars. According to Noto, worlds with permanent day and night are actually much more common than planets like Earth, which experience a regular day and night cycle.

“Many celestial bodies like moons and planets that are very close to their parent stars are what we call tidally locked,” he explains. “Meaning, as they spin around on their axes and orbit around their parents, those rates/frequencies match, leading to the phenomena like us only seeing one side of our moon.”

This constant orientation creates a dramatic temperature contrast across the planet. Instead of focusing on surface conditions alone, the researchers wanted to understand what happens deep inside the planet, specifically within the mantle, the thick rocky layer between the crust and the core.

Recreating an Alien Planet in the Lab

Rather than relying only on computer simulations, the team built a physical laboratory model to mimic the interior of a tidally locked planet.

“Building an actual exoplanet in the lab wasn’t in the budget,” Noto jokes.

Instead, the researchers used a tabletop rectangular tank filled with viscous glycerol and tiny thermochromic liquid crystals that change color as temperatures shift. Similar experimental systems have long been used to study how heat moves through slow moving materials, making them useful stand ins for the rocky interiors of planets.

Unlike weather or ocean currents, which are strongly influenced by Earth’s rotation and gravity, convection inside a rocky mantle is driven mainly by differences in temperature and density. To reproduce those conditions, the team installed four thermostats around the tank to heat and cool different regions, creating temperature gradients similar to those expected between the permanently illuminated side, the permanently dark side, the surface, and the deep interior of a tidally locked exoplanet.

A Planetary Heat Engine

The experiments revealed a remarkably stable pattern. Hot material consistently rose beneath the day side, flowed across the upper region, cooled as it reached the night side, then sank before returning through the lower mantle. The result was one continuous circulation loop that behaved like a steady planetary heartbeat.

“It’s not chaotic like Earth’s mantle,” Noto says. “It’s slow and steady. Predictable. Kind of boring — but in a good way.”

The researchers also observed occasional mushroom shaped plumes rising from the heated base of the tank. Unlike volcanic hotspots on Earth, such as those beneath Hawaii or Iceland, these plumes remained fixed in one location rather than drifting over time.

Measurements of heat transport, known as Nusselt numbers, were comparable to those seen for Earth’s mantle. That finding suggests some tidally locked exoplanets could maintain localized geothermal environments that provide conditions favorable for life, particularly in more temperate mid latitudes.

What This Could Mean for Alien Life

The steady circulation pattern may influence more than just surface temperatures. Noto believes it could also affect the movement of a planet’s liquid core, potentially generating magnetic fields that differ from Earth’s familiar dipole field.

“That’s something we couldn’t test in this experiment,” he says, “but it’s an exciting direction for future work.”

Looking Beyond Other Worlds

Noto and Ulloa are continuing to develop similar laboratory models to investigate a wide range of geophysical processes. Earlier research from the Penn GEFLOW Lab explored how heat and mass move through confined spaces, providing new insight into the role of fluids in hydrothermal systems.

“We are planning on further extending the experimental methods to delve deeper into different systems on our planet in different contexts, the possibilities are, quite literally, out of this world,” says Noto.

Daisuke Noto is a postdoctoral researcher in the School of Arts & Sciences at the University of Pennsylvania.

Hugo Ulloa is an assistant professor in the Department of Earth and Environmental Science in Penn Arts & Sciences.

Other authors include Takehiro Miyagoshi and Takatoshi Yanagisawa of the Japan Agency for Marine-Earth Science and Technology; and Tomomi Terada and Yuji Tasaka of Hokkaido University.