ESA Gaia mission makes billion star galaxy map but cannot detect Dyson Swarms

The European Space Agency Gaia mission will detect all celestial bodies down to magnitude 20. Gaia measures the positions, distances, space motions and many physical characteristics of some one billion stars in our Galaxy and beyond. For many years, the state of the art in celestial cartography has been the Schmidt surveys of Palomar and ESO, and their digitized counterparts. Gaia provides the detailed 3D distributions and space motions of all these stars, complete to 20th magnitude. The measurement precision, reaching a few millionths of a second of arc, is unprecedented. This allows our Galaxy to be mapped, for the first time, in three dimensions. Some 10 million stars will be measured with a distance accuracy of better than 1 percent; some 100 million to better than 10 percent.

Gaia’s resulting scientific harvest is of almost inconceivable extent and implication. It will provide detailed information on stellar evolution and star formation in our Galaxy. It will clarify the origin and formation history of our Galaxy. The Gaia results will precisely identify relics of tidally-disrupted accretion debris, probe the distribution of dark matter and establish the luminosity function for pre-main sequence stars. They will also help to detect and categorize rapid evolutionary stellar phases, place unprecedented constraints on the age, internal structure and evolution of all stellar types, establish a rigorous distance scale framework throughout the Galaxy and beyond, and classify star formation and kinematical and dynamical behavior within the Local Group of galaxies.

Gaia will detect a large number of isolated brown dwarfs. Luminosities of brown dwarfs fade rapidly to very faint absolute magnitudes, the lighter brown dwarfs being more sensitive to this effect. It is clear that brown dwarfs detected at G less than 20 mag will be strongly biased towards very young objects and those in the upper mass interval. Young brown dwarfs are however visible at relatively large distances. Old brown dwarfs will only be visible if they are nearby.

Gaia would not be able to detect Dyson Swarms

Arxiv – Dyson Spheres around White Dwarfs (16 pages)

A Dyson Sphere is a hypothetical structure that an advanced civilization might build around a star to intercept all of the star’s light for its energy needs. One usually thinks of it as a spherical shell about one astronomical unit (AU) in radius, and surrounding a more or less Sun-like star; and might be detectable as an infrared point source.

Dyson Spheres could also be built around white dwarfs. This type would avoid the need for artificial gravity technology, in contrast to the AU-scale Dyson Spheres. Researchers show that parameters can be found to build Dyson Spheres suitable –temperature and gravity-wise– for human habitation. This type would be much harder to detect.

If a Dyson Sphere was built around the Sun, e.g. with same radius (1 AU) as Earth’s orbit, it would receive all the power of the Sun, 3.8 × 1026 Watts, in contrast to the power intercepted by Earth, 1.7 × 1017 Watts. These numbers can be compared to the current power consumption of Earth, 1.7 × 1013 Watts.

The simplest form of the Dyson Sphere, a solid spherical shell, is problematic: It would be subject to unacceptably large stresses and its equilibrium around the star is neutral at best. Therefore, variants were suggested where the “sphere” actually consists of pieces in independent orbits (A “Dyson Swarm”). Another consideration is gravity: If the sphere were built in the Sol system with 1 AU radius, the gravity due to the Sun would be only 5 × 10−4 g, so humans could not live on it without either genetic modification to become compatible with microgravity, or a technology of artificial gravity.

If we lived on a 1 AU Dyson sphere, the Sun would look the same as it did from the surface of Earth. However, such a sphere would have a temperature of ∼400 K, since the infrared-emitting surface of the Earth is four times the the sunlight-receiving cross-section, while for the Dyson Sphere, the two surfaces are equal.

A White Dwarf Dyson sphere could be made with the right gravity and temperature and be easier to build while still increasing living space by 100,000 times.

Beings living on the Dyson Sphere would live on the outside of the sphere, using energy collected on the inside surface, e.g. photovoltaically. This means that they will either have to use artificial lighting, or light pipes.

A White dwarf dyson sphere with Earth-like density, radius of 3 × 106 km and thickness of 1 meter, we find a mass of ∼ 6 × 1023 kg, slightly less than the mass of the Moon. Obviously
this is a small fraction of the usable mass in the solar system. The mass of one terrestrial planet will easily give a 10 meter -thick shell, so that the inhabitants will not worry very much about accidentally puncturing it.

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