A long, long time ago, in a galaxy far away... There lived a great and powerful civilisation who built a dyson sphere around the smaller of two stars in a binary star system and built a habitable world for themselves around the outside.

Their new home orbited the larger star at a sufficient distance to provide Earth-like levels of insolation while the core star provided Earth-like gravity and all the power and space they could ever need.

Just how small could their new home have been?

(The dyson sphere is capable of keeping itself balanced around the core star and keeping the surface at a livable temperature)

  • $\begingroup$ This very much depends on star's luminosity. Would you count brown dwarf as star? $\endgroup$ – Alexander Mar 2 '18 at 21:44
  • $\begingroup$ @Alexander as long as it was pretty stable, I... guess so? $\endgroup$ – Samwise Mar 2 '18 at 21:49
  • $\begingroup$ Stability of a Dyson sphere would be defined by the technology that is used to build it. While sphere's radius is a factor, many other factors (like if it's rigid or soft) are more important. $\endgroup$ – Alexander Mar 2 '18 at 22:13
  • $\begingroup$ Why a rigid sphere when a bubble would have millions of times the living space and could be built around any size star. $\endgroup$ – skout Mar 3 '18 at 0:56

There is actually a paper on this. Click Here for PDF

Quick answer: 10^6 kilometer-scale Dyson Sphere

Depending on the specific white dwarf size of Dyson Sphere will be subject to change enter image description here

Shamelessly stolen from https://www.centauri-dreams.org/2015/03/23/white-dwarfs-and-dyson-spheres/

The White Dwarf Alternative

We have no Dyson sphere detections as of now, but speculative work on the concept continues, as revealed in a new paper from İbrahim Semiz and Salim Oğur (Boğaziçi University, Istanbul), forwarded to me recently by Adam Crowl. The duo posit a new take on Dyson spheres in which they are built around not G-class stars like our Sun but white dwarfs. Building around a white dwarf offers a number of possible solutions to Dyson sphere problems. And it turns out there are many of these.

Consider: If we somehow built a true sphere in the Solar System with a 1 AU radius, the gravity of the Sun would, according to the authors, be a miniscule 5 X 10-4 g. Inhabitants would be faced with microgravity. Rotating a Dyson Sphere would be one way out of the problem, but doing this would leave the equatorial regions as the truly usable surfaces, which would make it more sensible to build a ring-like structure in the first place rather than an all encompassing sphere that was largely useless. A system of independently rotating rings might be imagined but seems gratuitously complex.

The authors are aware of the instability that would plague both a Dyson sphere and a ring, but their paper isn’t about finding solutions to these problems but arguing for a different central object, which has advantages of its own. A white dwarf is much smaller than a G-class star, but applying Dysonian principles here would still give us a similar way of capturing energy while providing, by the authors’ estimate, 105 times the living area of a planet on the outside shell while not subjecting inhabitants to microgravity. A possible scenario is a civilization surviving the red giant stage of its star and returning to construct a Dyson Sphere around the white dwarf that eventually emerged.

From the paper:

…the red giant stage is also quite long, about a billion years for a solar-mass star (it decreases with mass), so it might seem that life/intelligence/civilization could also develop during that stage. However, conditions like radiative flux and stellar wind, even the mass of the star, are quite variable during the red giant phase, as opposed to the main-sequence period, when they are stable. Hence, while the astronomically-long-term outlook of an intelligent civilization is subject of conjecture, a civilization set to build a Dyson Sphere as discussed in this work would probably arise during the main sequence period of its star, and find ways to survive the red giant stage; maybe temporarily migrating to an orbit farther from its star, either to a planet, or failing/rejecting that, to orbital habitats a la O’Neill. In fact, such an effort would provide the experience needed before undertaking the construction of the Dyson Sphere around the eventual white dwarf.

We wind up with a 10^6 kilometer-scale Dyson Sphere with the inhabitants living on the outer shell as an alternative to the more common Dyson Sphere of fiction and speculation, one that would still be theoretically detectable through its infrared emissions but a much greater challenge because of its lower power. Its smaller size also means the white dwarf Dyson Sphere needs less construction material, with a 10-meter thick shell requiring approximately the mass of a single terrestrial planet. The required compressive strength of building materials for such a rigid sphere is also higher, demanding an extra means of support about which the authors choose not to speculate.

  • $\begingroup$ Good work in shamelessly stealing. It's an excellent paper. You've done a good job explicating it. Plus one for well done. $\endgroup$ – a4android Mar 3 '18 at 3:57

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