How quickly does Freeman Dyson respond to emails

Mind game: Dyson spheres around white dwarfs

Istanbul / Cambridge - The concept is more than half a century under its belt and its inventor was not even completely serious - but it is still one of the most popular motifs for science fiction novels and is even discussed by astronomers: In 1960, the British physicist Freeman Dyson presented his idea of ​​how to get the optimal energy yield from the light of a star.

The idea

Take one or more celestial bodies from asteroid to planetary size and use this raw material to build a sphere that surrounds the star. This gives you a gigantic area that is available for settlement, agriculture and energy generation.

Since then, the idea has haunted literature in various versions: least of all in the one that Dyson actually had in mind, namely as a synchronized swarm of individual objects orbiting the star. More often than actual spherical shells and in all conceivable variants in between.

Search with obstacles

In 2012, the US astrophysicist Geoffrey Marcy, after accepting a SETI-affiliated professorship at the Institute of Astronomy at the University of California, said that searching for traces of Dyson spheres in the search for extraterrestrial intelligences could be a sensible strategy . SETI ("Search for Extraterrestrial Intelligence") had previously ignored this possibility for a surprisingly long time. In cooperation with the Fermi National Accelerator Laboratory (Fermilab) in Illinois, where infrared traces of such spheres had been searched for, a corresponding concept was finally presented.

So far none have been found, otherwise we would have already reported about them. Or maybe you looked in the wrong place. The two Turkish physicists Ibrahim Semiz and Salim Ogur from Bogazici University in Istanbul recently presented a study in which they propose to focus on white dwarfs instead of stars similar to the sun as before.

According to the common astronomical view, white dwarfs were once stars that resembled our sun. They are what remains of these stars after they have largely used up their hydrogen supply, expanded into red giants and shed their outer gas shell. What remains is a faint star whose size is closer to the dimensions of rocky planets.

Advantages and disadvantages

The habitable zone around such a star - that is, where a Dyson sphere would be placed - is much closer to the star than the distance between the earth and the sun. According to the calculations of Semiz and Ogur, "only" material in the mass of the moon would be used to construct a one-meter-thick sphere around the star. As an additional goodie, there would be gravity conditions on a smaller sphere that are much closer to those on earth than in a giant sphere at the level of the earth's orbit.

But the matter also has a disadvantage - not for the hypothetical builders of a Dyson sphere, but for us who are looking for it: The method practiced by SETI and Fermilab searches for infrared traces that deviate from all known natural infrared sources. Because of the small amount of energy that a white dwarf emits, such traces would be much smaller and therefore more difficult to find than with a sun-sized specimen. (red, derStandard.at, April 4, 2015)