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To find life is, perhaps, the main and most desired goal of astronomy, preferably reasonable, somewhere outside the Earth. Given the ease with which life spreads and multiplies on our home planet, as well as the availability of ingredients for life throughout the universe, it is difficult to conclude that we are alone in the universe. In the galaxy alone, the Milky Way is about 400 billion stars, each with its own unique history and chances of life. Despite how technologically advanced people have become, the search for extraterrestrial civilizations is unsuccessful, perhaps because technologically advanced civilizations do not communicate in the way that we are used to. But a sufficiently advanced civilization could build a sphere around its sun – the Dyson sphere – to absorb 100% of its energy. Incredibly, we have the technology to detect them. If, of course, they exist.
Roy Dyson is seen as a step towards the Dyson sphere, when light is blocked by a series of spacecraft flying in front of a star.
On Earth, the amount of energy available to us is determined by the amount of sunlight incident on the surface of our planet. At a distance of the Earth from the Sun, this is roughly equivalent to 1300 watts per square meter, but falls to 1000 if the light is forced to pass through the atmosphere. If we covered the space above the atmosphere of the Earth with solar panels, we would collect 166 million gigawatts of energy, constantly, all over the Earth. This is an enormous amount of energy: even a second of such a flow could provide earthlings with energy for a whole year. But only part of this energy is produced by the Sun. There are other ways.
The concept of a space solar power plant has existed for a long time, but no one even dared to think about an array of billions of kilometers away. The sphere or swarm of Dyson would go even further, surrounding or wrapping the panels themselves Sun.
For example, we could build a swarm in space to collect even more solar energy. Imagine a large fleet of spacecraft that move in a ring or a series of rings with a large collection area. This energy could be used for any purpose: it could be sent to Earth in a beam, it could be used on site to create a network throughout the solar system, or for interplanetary or interstellar communications. That’s where the idea of the mega-structure of aliens originated – which was suggested as one of the explanations for the phenomenon of obscuring the star Tabbi.
However, the most ambitious megastructure is the so-called Dyson sphere: a shell around a star that absorbs all of its energy. We could do this by devouring a small planet like Mercury, decompose it into iron and oxygen and create a reflective surface of hematite. If the alien civilization did the same, the shell will completely hide the star, making it virtually undetectable.
Dyson’s sphere will completely cover the star, absorbing all its ultraviolet and visible radiation. Pass only infrared radiation and long waves.
In any case, undetectable for telescopes operating in the visible spectrum of light, because such a sphere would completely block the light of the star. But even a highly reflective surface must absorb some of the energy. And if the energy is absorbed with time, it needs to be redirected somewhere to maintain a stable temperature. Therefore, the energy must go out into the universe, even if there is no visible light. As the Earth emits energy at night in the infrared, Dyson’s sphere will also be.
At night, the Earth emits electromagnetic signals, but the overwhelming majority of them are in the infrared range, as sunlight and heat absorbed during the day are sent into space.
The European Space Agency recently released a huge data set from the most powerful satellite that ever charted and explored the stars of the Milky Way: Gaia. He managed to gather information about 1.7 billion stars in our galaxy, allowing us to create the most complex 3D map of the stars of the Milky Way. This is by no means all of the stars, but an order of magnitude greater than what was recorded before.
One of the magnificent things Gaia was able to measure was the color and magnitude of a multitude of stars, from dim red dwarfs (and even brown dwarfs) to stellar remains like white dwarfs, main sequence stars, giants and supergiants that glow the brightest. But Gaia observed not only in the visible, but also in the near infrared spectrum, and therefore saw objects that are hidden from the eyes of people. Among them, super-cold stars, both giants and dwarfs. And Dyson spheres, if they exist and have certain temperature / luminosity profiles.
A large, bold line that crosses the diagram from the bottom left to the upper right corner is the main sequence in which the stars synthesizing hydrogen into helium are located. To the right at the top are stars in a giant or supergiant phase: they burn heavier elements and expand to much larger sizes. Even though they are brighter, their temperature is lower, because the energy dissipates over a large area that emits energy.
Dyson’s sphere does almost the same thing, but with an ordinary or a low-mass star. You create a large surface area, with which the star energy will escape, and it emits at a lower temperature, while giving the same total energy. Infrared signature, in theory, should give us a similar sphere, but the satellite Gaia prompted another version disclosed by Eric Zakrisson: the discrepancy of the distance based on luminosity, with the distance of the parallax.
The parallax method, used since the 1800s, involves observing a change in the position of the star that is next to a farther, background star. If the parallax and star luminosity distances do not coincide, this can explain the mega-structure of the aliens … or that the star is in a binary system.
When you draw a conclusion about the distance based on the observed light, and then conduct the measurement in a completely different manner (using geometry), the two numbers must coincide. The fact that Gaia saw several discrepancies can speak about different things, including the structures of aliens. Human nature is such that we are immediately searching for the most fantastic explanation. But a more mundane and reasonable reason will be the presence of double companions in stars: this is a fairly common phenomenon in the universe. The absence of redundant infrared radiation, necessary for structures such as the Dyson sphere, leads us away from the hypothesis of extraterrestrials and their structures.
A number of observatories, including the Gaia spacecraft, possess technologies that are in principle capable of detecting Dyson spheres several thousand light-years from the Earth, assuming that they are at the same distance from the Sun-type star as Earth from our luminary. The red dwarf star should be visible in the eyes of Gaia with a small sphere of Dyson at a distance of hundreds of light years, but a giant or supergiant star will be visible almost everywhere in the galaxy. Among the 1.7 billion objects collected by Gaia, one could find Dyson’s spheres in the process of construction. And by comparing data on infrared observatories, one could find already ready Dyson spheres, which emit enough energy. At the time of this article, however, no Dyson sphere was found in the Milky Way.
But this does not mean that they are not; it means that if they are, we have not yet seen them. Spheres of Dyson can be farther than Gaia sees, being located near smaller stars. Infrared observatories such as WISE define search boundaries, and next-generation observatories can potentially detect the signature of heat removal from such an object.
Given the complete set of observatories that have surveyed the sky, it can be relatively safe to say that we have not yet found any Dyson sphere at the moment. Probably, somewhere and there are reasonable aliens who use all the energy of their stars entirely and create huge transplanetary empires, but there is no proof to this. One can make only one reasonable conclusion: our galaxy, as far as we can judge, does not have these giant extraterrestrial designs.