Dyson sphere

A Dyson sphere (pronounced [ ˌ daɪ̯sn̩ sfɛ ː rə ], named after Freeman Dyson ) is a hypothetical construct that completely encloses a spherical star in the ideal case to absorb the energy or redirect to optimally utilize can.

Background

Such a structure was first described by the physicist Freeman Dyson in the June issue of the journal Science in 1960. The aim was to search in the search for advanced alien intelligences by infrared sources because the energy of the respective central star must be issued again even after their full use for the purposes of that civilization (see conservation of energy ). That would, after the power of the short wavelength light has been used in order to reduce the entropy of the system, be done in langwelligerer form and therefore in the infrared range.

The original proposal by Dyson did not elaborate on the details of the construction of such an object, but instead focused more on the more fundamental issue of how an advanced civilization can expand its energy production on the achievable for a planetary system maximum. Such a civilization would as type II according to the Kardashev scale, which was developed by the astronomer Nikolai Kardashev, classified.

Although the Dyson Dyson sphere is regarded as the "inventor", he was by his own account of similar ideas in Olaf Stapledon's science fiction novel Star Maker, which appeared in 1937, inspired. An even earlier possible excitation for both Stapledon as well as Dyson is the Bernal Sphere, which was first described in 1929 by John Desmond Bernal. Dyson himself described his theory later as a " joke" (joke ).

Properties

The star inside a Dyson sphere would not be directly visible, but they would themselves emit a corresponding to the energy output of the star amount of energy in the form of infrared radiation. Dyson has suggested that astronomers look for such anomalous " stars " to discover highly advanced extraterrestrial civilizations.

The symmetrical construction around the central star around allows a non-powered operation of the Dyson sphere, only course corrections are necessary.

Types

There are several types of Dyson, " spheres ", which have been proposed.

The Swarm

The most realistic and most original ideas Dyson's corresponding form is the Dyson Swarm. It consists of a large number of independent solar collectors orbiting the star. They may differ in size and shape and, if so distinct habitats. It has made ​​a number of proposals for possible distribution patterns, each with its own advantages and disadvantages. For example, using a Dyson swarm in disc form, the kinetic energy of its raw material from best, consisting primarily of asteroids that orbit close to the plane of the ecliptic in approximately the same direction of rotation. In any case, some collectors would spend part of their circulation in the shadow of others, and thus the efficiency of the swarm reduce slightly. The ratio of the Earth's orbital radius of 149.6 million kilometers to the solar diameter of 1.3927 million km is about 107.4. This means that at the earth's orbit radius of the core of the shadow of a solar panel, adopted as a circular disk about 107.4 times as long as the diameter of the solar panel. At a distance from the 1,074 times the diameter of the solar panel can thus be as low as 1% of the maximum shadowing because, viewed from there, the apparent diameter of the solar collector is 10 times less than the apparent diameter of the sun.

The shell

A further form, the solid shell that completely encloses the star. This variant is very popular in science fiction (as an example, the episode " Relics Enterprise " series Star Trek - called The Next Generation ) and is often described with an atmosphere on the inside, which for a massive habitat biological organisms forms. With the laws of physics known today, however, such an atmosphere is not realizable as a symmetric hollow sphere into its interior does not have a gravitational field, and the gravitation of the sun would be falling into the sun, the atmosphere and all moving objects. An atmosphere on the outside would be possible, but you would have to get by there without direct sunlight. In addition, the gravity of the sun would be only 5.93 · 10-3 m/s2 at the Earth's orbit radius. Due to the occurrence of enormous tangential forces a purely static implementation with today's available materials ( eg steel) due to lack of compressive strength is not feasible. It is unclear whether using new materials (eg nanoporous metal foams) the minimum required compressive strength of about 10 MN / mm ² can ever be achieved. It is also conceivable components of the shell would be to rotate around the sun, the resulting centrifugal forces could relieve the shell and reduce the compressive strength required.

Going beyond the aforementioned Star Trek episode Dyson said: " Actually it what sort of fun to watch it. . It's all nonsense, but it's quite a good piece of cinema " (about: That was actually quite entertaining While it is all nonsense, but good movies. . )

The bladder

A third form is the " Dyson bubble" that consists only of very little mass and is kept stable by the radiation pressure of the Sun and the solar wind. A supporting structure is not necessary. The adjacent pictorial representation the central star can be seen to better understanding. In fact, however, the material of the bladder would absorb most of the visible light for the purpose of energy and thus the collapse rating.

Calculation of the supported by the radiation pressure mass

Radiation pressure depends on the absorbed or radiated power per area. The wavelength of the radiation is irrelevant.

For example, at a radius of 149.6 million km (equivalent to Earth's orbital radius), the solar constant, 1367 W/m2 and the resulting radiation pressure (for absorption) 4.56 · 10-6 N/m2. The counterweight is the gravitation of the sun with 5.93 · 10-3 m/s2. In order to keep a segment of the bubble in the balance, the two oppositely directed forces must cancel. This would be the case with a surface with 7.69 · 10-4 kg/m2. The radiation pressure support from the bladder segment against gravity. This mass per area also applies to all other distances from the sun, because the radiation pressure and the gravitational take outwardly alike from ( with the inverse of the square of the solar distance ). Individual objects that float through the radiation pressure of the sun without enough to circle quickly are called Statiten (as opposed to satellite ).

For a Dyson bubble with the Earth's orbital radius is obtained at a total of 2.81 · 1023 m2 has a mass of 2.16 · 1020 kg. This is roughly the mass of a larger planetoid.

When the density of the material used would be 1 g/cm3 ( about the density of a plastic film ), would then be the layer thickness of only 769 nm Dyson bubble This corresponds to the wavelength of red light near the infrared range. The resulting reduction in absorption capacity of this thin layer would also reduce the supporting radiation pressure.

Amplifying the radiation pressure

The entire outer surface of the bladder are exactly the same radiation power on how they created the sun, just 1 psol. It turns up a radiative equilibrium. This also applies to modified spectrum.

In a double-sided black Dyson bubble which has the consequence that their entire inner surface emits 1 psol, because at low film thickness, the material has inside and outside the same temperature. The pressure effects of the votes according to external and internal radiation cancel each other.

The given inwardly radiation power is ultimately absorbed by the ( respective opposite side of) the bubble itself again. Thus, the inner surface absorbs 1 psol from the sun and additionally 1 psol of their own respective opposite inner surface, so together 2 psol. The radiation pressure is therefore twice as large as that of a single awning and so can support twice the mass.

An additional pressure caused by the reflected radiation on the inside of the radiation. Although ultimately, the entire output from the solar radiation is absorbed at the inside of the bladder, but in the meantime parts of this radiation can be reflected back and forth several times. Each reflection increases the overall radiation pressure, and thus the mass can be supported. With highly reflective inner coating, for example aluminum, would take as a result of multiple reflection, the radiation density inside the Dyson bubble very high values. A heating and expansion of the outer layers of the sun, however, would result.

The ring

The ring surrounding a star, for example, with a radius of about one Astronomical Unit. Thus, the ring has an incomplete shell dar. Because of the enormous tangential is a realistic design with a balance of the centrifugal and gravitational force is possible, which means that there is on the surface of the ring gravity. The edge of the ring and the gravity, the centrifugal force world the sun show not exactly in the opposite direction, resulting in a force that attempts to reduce the width of the ring world. If a compressive strength of 100 N/mm2 and a density of 1 g/cm3 is assumed ( the ratio of compressive strength and density reach today many materials ), this ring world may be 4.5 million kilometers wide, which corresponds to 3 % of the Earth's orbital radius. At the edge of the ring world to accelerate from 9:10 -5 m/s2 would act in the direction to reduce the width of the ring world, which corresponds to 1.5% of the gravitation of the sun in the Earth's orbital radius. If the world would be cylindrical ring, the centrifugal force would be greater than the gravitational pull of the sun, which is dependent on 1/Radius2 at its edge. If the ring world would be a section of a sphere, then the gravitational pull of the sun would be greater than the centrifugal force, which depends linearly on the radius at its edge. The optimal shape of the ring world that is situated between these two forms, the direction of the pressure force at each location is parallel to the surface of the ring world, so that no bending moment occurs. An example from science fiction is Ringworld by Larry Niven, however, rotates much faster to generate artificial gravity by centrifugal force, and only 1.6 million kilometers wide.

Matryoshka brain

A matryoshka brain (English Matrioshka brain ) in turn is a bulbous collection of Dyson spheres, whose goal is not the maximization of habitable surface but maximum energy efficiency with which then a giant computer is running. The innermost sphere would be placed as close to the star as possible, and the outermost as far outside as yet energy from the temperature difference between the inner and the next empty space is possible.

The concept was designed in the late 1990s by the computer scientist Robert Bradbury. In science fiction literature, among others, it was made by Charles Stross known in his novel Accelerando.