A Dyson sphere is a spherical megastructure built around a star with the goal of capturing all of the energy output of the encased star and making that energy available to the controllers of the megastructure. Producing as much usable energy as possible is the idea.

If the encased star were artificially compressed or expanded, would the controllers of the Dyson sphere be able in increase the net energy output?

Note that the artificial compression or expansion would require energy, not only to initiate it, but to maintain it. The initial energy requirement may be ignored, but the energy used to maintain this effect would be siphoned off of the energy the Dyson sphere collects, hurting the net energy output.

Ignoring the details of how, you may assume the Dyson sphere is capable of absorbing 100% of the star's energy output, and is able to store, transmit, and use the energy it collects with 100% efficiency. The machinery used for the compression or expansion is built into the megastructure.

  • $\begingroup$ Dyson spheres are considered essentially impossible, and have been "replaced" by the concept of Dyson Swarms. Dyson himself does not appear to have intended to suggest an actual sphere as a structure, but something more like a swarm. $\endgroup$
    – StephenG
    Jul 6 '17 at 2:15
  • $\begingroup$ The post history should show that this question was deleted and then undeleted, both by me. That was a mistake; I meant to delete only my own answer. I apologize for any inconvenience. $\endgroup$
    – HDE 226868
    Jul 6 '17 at 20:52
  • $\begingroup$ Could you clarify if you want a higher net power (energy per unit time, possibly during a short period of time) or higher net energy (collected over possibly the lifetime of the star)? $\endgroup$ Jul 10 '17 at 12:42
  • $\begingroup$ @theindigamer - I am looking for higher net power over a short period, like a century or so. $\endgroup$
    – TheNewGuy
    Jul 12 '17 at 13:19

Yes, they could somehow increase the star's gravitation. This would accelerate its nuclear processes and the star would find a new equilibrium at a higher brightness. It requires energy to set up, but not necessarily any energy to maintain it; if, for example, you replaced the star's inert iron core with a denser element, that would be enough (provided the new core is stable, that is).

  • $\begingroup$ What do you mean when you say "the star's inert iron core"? Why would the star have an inert core? Or, to put it a different way, why would a star with an existing inert core be chosen as the sight of a Dyson sphere? Thanks $\endgroup$
    – TheNewGuy
    Jul 6 '17 at 22:59
  • $\begingroup$ Stars get their energy by fusing hydrogen to helium, but they also fuse light elements to heavier ones - helium to carbon, and so on. These accumulate in the core, and for large stars the process goes all the way up to iron, whose binding energy is such that its fusion does not supply energy any more. A small star will have very little iron, and iron could be used to increase its mass. Denser elements would be a safer bet. Of course you would require enormous amounts of matter - indeed a good proportion of a whole star's worth. $\endgroup$
    – LSerni
    Jul 6 '17 at 23:31
  • $\begingroup$ Adding 'pellets' of a higher density material (megatons) would have these pellets fall (eventually) to the core and thus cause a slight compression of the gases around the core. Add enough of these pellets, and the star would begin to burn more of itself, just because there would be more fusion going on. Short answer - drop a planet into the star. $\endgroup$
    – Hirahito
    Jul 7 '17 at 17:42
  • $\begingroup$ @LSerni, wouldn't you have fission if you put in atoms with higher nuclear masses for your new core? $\endgroup$ Jul 10 '17 at 12:40

The star's energy output perfectly equals it's gravitational binding energy because the energy output is what keeps the star from collapsing under it's own gravity, it is why stars eventually stop being stars when they no longer have a exothermic nuclear fusion reaction to fuel them. This is the equilibrium of energy output and size of the star. The star existing in this equilibrium means that altering the size in any way requires more energy than you can gain from the star due to the laws of thermodynamics.

Although the star exists in equilibrium, it does not mean that it doesn't have different energy levels that don't exist in nature. Stars theoretically can have locally stable energy states that are not the natural one that all stars share. Maybe if you were to add enough energy to the star to reach temperatures on Planck scale, you would reach different physics than we currently know and gain energy afterward. This wouldn't really make much sense because Planck temperature is 1.417×10^32 and even siphoning millions of stars will not give you enough energy to get to that point.


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