Written by Hitanshi Manisha Rakesh Nahar
This structure was first described in Olaf Stapledon's science fiction novel "Star Maker" in 1937 - "Not only was every solar system now surrounded by a gauze of light traps, which focused the escaping of solar energy for the intelligent use so that the whole galaxy was dimmed, but many stars that were not suited to be suns were disintegrated, and rifled of their prodigious stores of sub-atomic energy."
Dyson Spheres are theoretical constructs that harvest the entire energy output of a given star by completely enclosing it. Inspired by the novel "Star Maker", Freeman Dyson's paper "Search for Artificial Stellar Sources of Infrared Radiation" suggested a method of orbiting structures (which he referred to as a shell) designed to intercept and collect all energy produced by the Sun [1]. Soon, this topic gained popularity and scientists studied it as a part of their Search for Extraterrestrial Intelligence Research (SETI).
The aim is to collect the huge amount of energy released by the host star. The photovoltaic effect (the direct conversion of light into electricity at the atomic level) is a primary technique that can be used here. These structures are hypothetical. Trying to build one is far beyond human ability. Dyson's paper stated that this sphere of collectors would be a way to collect energy used by future human civilizations or possibly some advanced alien civilizations. The Type II Kardashev Civilization is the one that is capable of harnessing the energy radiated by its own large star with an energy consumption of 4×10^33 erg/sec i.e., a civilization that can successfully build this hypothetical structure, Dyson Sphere [2].
A type II Dyson sphere would be totally opaque - unless it had openings. They will be invisible from a distance, just a black disk in the sky. But they would shine powerfully in the infrared, as the waste heat from the internal processes radiates away. The apparent temperature would be T = (E / (4 pi r^2 eta sigma))^1/4 where E is the energy output of the sun, r is the radius of the sphere, eta the emissivity, and sigma the constant of Stefan-Boltzman's law. The sphere won't heat up. Because of thermodynamics, the sphere radiates energy until it reaches equilibrium [3].
In theory, if eta is very low the interior of the sphere could become as hot as desired, but this is unlikely since the material of the sphere would start to melt or evaporate if the temperature moved above 2000-3000K or so. And if the surface of the star became hot enough, the outer parts of the star would expand and a new thermal equilibrium set in with less internal energy production. If the sphere was a perfect energy container the star would eventually expand until its fusion processes ended; if the temperature was lowered (by energy use) fusion would resume until an equilibrium was reached - a bottled star. It should be noted that at 1 AU, the energy flux is around 1.4e3 W/m^2, which calculates as around 395 K, or 122 degrees C if the sphere is a blackbody. This is a bit too hot for an earthlike biosphere (Earth is cooled by its rotation, which effectively halves the energy flux, and its spherical shape, which lowers it further), and a Dyson shell needs some rather exceptional cooling to work [3].
By looking carefully for deficits or excesses in the light of thousands of stars, one estimate suggests up to 10,000 stars could host Dyson spheres within a radius of about 16,000 light-years of Earth (by comparison the distance to the Milky Way’s centre is about 26,000 light-years) [5].
To conclude, there are no Dyson Spheres observed yet. The existence of such a system of collectors would alter the light emitted from the star system. Collectors would absorb and reradiate energy from the star. The wavelength of radiation emitted by the collectors would be determined by the emission spectra of the substances making them up, and the temperature of the collectors [4].
References:
Wikimedia Foundation. (2022, November 29). Dyson sphere. Wikipedia. Retrieved December 1, 2022, from https://en.wikipedia.org/wiki/Dyson_sphere
Wikimedia Foundation. (2022, November 22). Kardashev scale. Wikipedia. Retrieved December 1, 2022, from https://en.wikipedia.org/wiki/Kardashev_scale
Dyson Sphere FAQ. Aleph.se. (n.d.). Retrieved December 1, 2022, from https://www.aleph.se/Nada/dysonFAQ.html#WHAT
Dyson, F. (n.d.). Search for artificial stellar sources of infrared radiation . Retrieved November 30, 2022, from https://www.science.org/doi/10.1126/science.131.3414.1667
Gunn, D. A. (2022, November 5). Dyson spheres: How humans (and aliens) could capture a star's energy. BBC Science Focus Magazine. Retrieved December 1, 2022, from https://www.sciencefocus.com/space/dyson-spheres/
Tate, K. (2014, January 14). Dyson Spheres: How advanced alien civilizations would conquer the galaxy (infographic). Space.com. Retrieved December 1, 2022, from https://www.space.com/24276-dyson-spheres-how-advanced-alien-civilizations-would-conquer-the-galaxy-infographic.html
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