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So, a civilization built a massive Dyson Sphere around a supergiant star. As the star ages, it begins to fuse iron. At this point, the force of radiation pressure cannot prevent core collapse, and thus the supergiant goes supernova. So I am wondering, what would happen to the Dyson Sphere? Would it get blown apart?

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    $\begingroup$ If you wait at least 24 hours before accepting an answer you have higher chances of getting more and better answers. $\endgroup$
    – L.Dutch
    Dec 31 '20 at 14:33
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    $\begingroup$ Schlock mercenary web-comics dealt with a related scenario - a Buuthandi - solar-sail based non-rigid Dyson sphere. As an emergency procedure, the structure can break into many sections of habitats and structures - each with it's own very large sail - allowing them to ride the solar wind (or is it stellar wind for another star?) away from the star. Assuming the impending super nova is predicted early enough, this strategy may allow the inhabitants to reach to a safe distance. $\endgroup$
    – G0BLiN
    Dec 31 '20 at 21:45
  • $\begingroup$ Presumably the civilization will just beam out the iron and replace it with hydrogen. They'll need a lot of hydrogen, and there aren't that many sources for that much hydrogen... probably CostCo... $\endgroup$ Jan 1 at 4:20
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    $\begingroup$ they'd be pretty dumb to build around such a short lived star. $\endgroup$
    – ths
    Jan 2 at 1:39
  • $\begingroup$ @ths Maybe the energy output of this star is better? $\endgroup$ Jan 2 at 21:38
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Mandatory What if quote:

Rule of thumb for estimating supernova-related numbers: However big you think supernovae are, they're bigger than that.

Here's a question to give you a sense of scale:

Which of the following would be brighter, in terms of the amount of energy delivered to your retina:

  • A supernova, seen from as far away as the Sun is from the Earth, or

  • The detonation of a hydrogen bomb pressed against your eyeball?

Applying the physicist rule of thumb suggests that the supernova is brighter. And indeed, it is ... by nine orders of magnitude.

I am pretty sure the supernova, with the sheer amount of photons blowing out in its surroundings while exploding, would simply plasmify the Dyson sphere, way before the radiation could have any chance of pushing it apart.

If you want to estimate a safe distance, as PCman said in their comment, consider that a supernova can emit about $10^{44}$ Joules. The Sun's routine output is $10^{26} \ J/s$. The peak period of a supernova is about 6 hours, so that $10^{44}$ joules is spread over about 21000 seconds. Thus, a supernova would only be about $4\cdot10^{13}$ times brighter than the normal sun at its peak. Assume your Dyson sphere can take 10x normal sunlight intensity. At a distance of only 2.2 million AU it will be safe. That's less than 55 000 times further than Pluto!

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  • $\begingroup$ How far would the Dyson Sphere have to be for it to not get vaporized, and how far for it to remain stable? $\endgroup$ Dec 31 '20 at 13:52
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    $\begingroup$ @fasterthanlight as a rough rule: supernova is about 10e44 Joules. Sun's routine output is 10e26 joules per second. Peak period of supernova is about 6 hours only, so that 10e44 joules is spread over about 21000 seconds. thus, only about 4e13 times brighter than normal sun. Assume your Dyson sphere can take 10x normal sunlight. At distance of only 2.2 million AU it will be safe. that's less than 55 000 times further than Pluto. $\endgroup$
    – PcMan
    Dec 31 '20 at 14:04
  • $\begingroup$ @PcMan I was editing the same in the answer... I will embed your comment $\endgroup$
    – L.Dutch
    Dec 31 '20 at 14:05
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    $\begingroup$ The problem here is that a Dyson sphere would have to be made of handwavium, so just wave the hands a bit more and make it impervious to the effects of temperature and pressure. Then calculate the effects of a supernova taking place inside an impervious shell... $\endgroup$
    – jamesqf
    Dec 31 '20 at 18:18
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    $\begingroup$ @fasterthanlight, a sphere encompassing a star will always intercept all its energy emission, no matter how far from the star it is (and neglecting absorption in interstellar medium). What changes is the energy per unit surface. $\endgroup$
    – L.Dutch
    Jan 1 at 16:55
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L.Dutch has already given you the answer, that the Dyson sphere would not survive the supernova, but I thought it would be fun to consider just how bad things would get.

The Dyson sphere has probably already suffered through quite a lot. To give it a shot at making it through the entirety of the star's life (up until this point), say that the star has a radius several hundred times the Sun (so a couple AU in size) and weighs in at around $20-25M_{\odot}$. This means that the Dyson sphere has to survive ablation by the winds of the star, which might have terminal velocities of $\sim2000\;\text{km s}^{-1}$. With mass-loss rates of, say, $10^{-6}M_{\odot}\;\text{yr}^{-1}$, that's not horrible compared with what's to come, but all the same, it's going to cause some wear and tear. It's quite likely that the megastructure will already be dealing with holes and could well be structurally compromised. It'll be hot, too - if the star has a luminosity of $\sim1000L_{\odot}$, the sphere will heat up to somewhere near 1300 Kelvin, which will probably melt some of its components unless they're adequately shielded.

Let's say that the luminosity of the supernova, in its initial stages, is $L\sim10^{44}\;\text{erg s}^{-1}$. If we use the Stefan-Boltzmann law and assume that the Dyson sphere has a radius of 3 AU, to encompass such a large star, we see that the Dyson sphere will quickly heat up to around 90,000 Kelvin, which is more than hot enough to vaporize the key constituents of the megastructure. (I actually wouldn't be surprised if the temperature is much higher - the assumptions that the Dyson sphere is a black body under these conditions, and is able to radiate efficiently, may not be called for. . .)

It's taken several minutes for the photons to reach the Dyson sphere, which has now been pulverized. The remnants will then be rammed by the outer layers of the star, which have been turned into ejecta of perhaps $\sim10M_{\odot}$ moving at speeds of $\sim10000\;\text{km s}^{-1}$. They'll take somewhere around 4-6 hours to reach the remains of the sphere, and will carry an enormous amount of kinetic energy. As the shock wave reaches 3 AU in radius, it will promptly sweep up the Dyson sphere and carry it off as it expands outwards into a supernova remnant.

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    $\begingroup$ Assuming you don't have a neutron star kicked out at .001c, as I recall reading about. That'll punch a hole. $\endgroup$
    – Joshua
    Dec 31 '20 at 23:26
  • $\begingroup$ @Joshua I wouldn't be too concerned by that; pulsar kicks are rarely above 1000 km/s and usually a bit lower, meaning that the ejecta will likely reach the remains of the structure long before the neutron star does. $\endgroup$
    – HDE 226868
    Jan 1 at 16:15
  • $\begingroup$ It's still going to punch a hole if anything's left by the time it reaches it. 1000 km/s is clearly going to overcome the dyson sphere's station-keeping ability. $\endgroup$
    – Joshua
    Jan 1 at 16:17
  • $\begingroup$ @Joshua True, but that would likely be only a tiny fraction of anything, even if most of the remains aren't swept up by the shock from the ejecta - the cross-section of a neutron star is roughly $10^{-16}$ of the surface area of the sphere, so I think it's fairly negligible, even assuming that that's a slight underestimate by a factor of a couple because of gravitational focusing. $\endgroup$
    – HDE 226868
    Jan 1 at 16:20
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It's completely unclear. Building a Dyson sphere takes technology beyond what is currently know, so we know nothing of the behavior of such technology. A super-nova would dump out massive amounts of energy beyond what the normal star would produce, but without specifying the technology and how it was used, you can't tell what it would do under excessive loads. For example, windmills are designed to run under certain wind conditions, but usually designed to disengage and furl their props under excessive wind conditions. What if a Dyson sphere were made using force-field technology? Overpressure might just "blow-through" the field w/out being captured, but do no damage as long as the field generators were intact. And then it would depend on how heavily the field generators were shielded.

If you're writing fiction, you can pick it either way: it survives or it doesn't. Then just make up some techno-babble reason for that to be true.

If you want to know for real? We don't know, because we don't know how to build a Dyson sphere, so can't tell what it will do under excessive load.

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