The Galaxy's Coldest “Stars” Might Actually be Alien Megastructures
mrpg writes:
The Coldest "Stars" in the Galaxy Might Actually Be Alien Megastructures:
Ever since physicist Freeman Dyson first proposed the concept in 1960, the "Dyson sphere" has been the holy grail of techno-signature hunters. A highly advanced civilization could build a "sphere" (or, in our more modern understanding, a "swarm" of smaller components) around their host star to harvest its entire energy output. We know, in theory at least, that such a swarm could exist - but what would it actually look like if we were able to observe one? A new paper available in pre-print on arXiv, and soon to be published in Universe from Amirnezam Amiri of the University of Arkansas digs into that question - and in the process discloses the types of stars that are the most likely to find them around.
Perhaps unsurprisingly, one of those types is a Red Dwarf. The most abundant type of stars in the Milky Way, they burn through their nuclear fuel incredibly slowly making them extremely long lived. With estimated lives in the trillions of years - far longer than the current lifetime of the universe - they are also relatively small compared to our own Sun. A Dyson swarm could be built around 0.05 to 0.3 AU away from its surface, with relatively low cost of material.
White dwarfs are arguably even better for material costs, and represent the second type of star that it's worth tracking. These are compact, dead remnants of stars like our Sun, which have shrunk down to have incredibly small radii - around 1% of their original star. In this scenario, a Dyson swarm could be built just a few million kilometers away from the surface of the star, alleviating much of the engineering challenge of build a supermassive structure around a larger star. They also radiate energy steadily for billions of years, essentially creating an effective long-lived power source.
But what would stars surrounded by such megastructures actually look like? Astronomers typically use a tool called the Hertzsprung-Russell (H-R) diagram to classify stars based on their temperature and luminosity. However, since a Dyson sphere would block all of a star's natural light, it would completely change where on the diagram it would fall. Energy can neither be created nor destroyed, so the sphere itself would have to emit the exact same amount of radiation away from itself as the star is putting into it. It just does it in the form of heat, or infrared light instead. So a Dyson sphere can really be thought of as a shell that absorbs a star's light, does something useful with that energy, and then emits it as heat.
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