Dyson spheres in the Milky Way: the discovered objects are not linked to extraterrestrial civilizations.

Most extraterrestrial life search projects, such as SETI, focus on radio signals from distant sources. However, recently scientists have broadened their search to include other forms of communication, such as gravitational waves, neutrinos, as well as megastructures like Dyson spheres, reports Phys.org.

The Swedish project "Hephaestus" is focused on searching for technosignatures in general, not just extraterrestrial signals directed towards Earth. Recently, a group of scientists from the University of Manchester examined candidates for Dyson spheres identified by the Swedish project.

Dyson spheres are megastructures first described by physicist Freeman Dyson. He suggested that advanced civilizations might create structures large enough to encompass their stars, allowing them to harness energy directly from them.

The "Hephaestus" project, led by Professor Erik Zackrisson, has found numerous candidates for Dyson spheres. A recent discovery was dedicated to 7 candidates located around M spectral class stars.

Such candidates may have entirely natural explanations. For instance, dust disks around stars can absorb light and re-emit it as infrared radiation. This would lead to an observed excess of infrared radiation, which according to Dyson's theory, is one of the signs of a megastructure's presence.

"You don't expect stars to exhibit radio emissions at such levels, and this mainly tells you that the radio emissions are likely coming from background (radio) galaxies. But then you also need a specific type of galaxy that is weak in the optical range but very bright in the infrared — the only galaxies I knew of that had such characteristics are hot galaxies hidden by dust," the researchers say.

Additionally, according to another theory, a true Dyson sphere might use radio emissions to dissipate waste heat. This led scientists to consider the possibility that these candidates could indeed be Dyson spheres.

As part of their investigation, the team checked data from the European VLBI Network (EVN) and e-MERLIN, searching for information on the brightest radio source (candidate G).

Thus, the scientists discovered that three candidates from the "Hephaestus" project had radio counterparts in astronomical databases. Therefore, the most logical explanation is that such signals, including candidate G, originated not from Dyson spheres, but from active galactic nuclei (AGN) in the background.

"They cannot belong to a single civilization. Otherwise, they would have to be connected in a swarm rather than scattered across the sky. We also realized that either all these civilizations developed similar advanced radio emission technologies, or the signals must arise from some form of natural interference. We suspect that these objects are located beyond the Milky Way, most likely being hot galaxies hidden by dust," the authors of the study add.

The results showed that some Dyson sphere candidates selected by the "Hephaestus" project are contaminated by bright radio sources. However, this does not exclude the remaining six candidates and highlights the importance of thorough analysis for each of them.

As a reminder, 8 strange signals from space of unknown origin have been detected. Scientists, using artificial intelligence, have discovered thousands of signals from space, but only a few of them could have been sent by extraterrestrial beings.