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Things like Dyson spheres need a whole lot of raw material, which is rather difficult to come by, since the elements needed for good structural steel are scattered fairly thinly into the universe upon the death of the stars that produce them.

The obvious solution is to somehow get at the approximately one solar mass of iron while it's still cooking, or at least before it has time to fully disperse, which would be before the star turns into a neutron star which is even harder to mine. Supposing you have the world-smelters and transport capacity to strip mine several solar systems' worth of planets, how would you go about shutting a star down so you can get at the layers of heavier elements of the inner layers of the star?

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    $\begingroup$ Alas, the stage where the star is producing iron only lasts about one day before the supernova. It's probably easier to collect it from the supernova remnant; some kind of magnetic scoop should help you collect it if you catch it while it is still ionized. $\endgroup$
    – brendan
    Commented Nov 2, 2019 at 23:24

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It is called star lifting, and is a known concept. Basically, you generate a magnetic field which channels solar radiation through the poles. The magnetic field is created using orbiting electromagnets powered by the sun itself. There are three variations of this technique in Isaac Arthur's Youtube series.

https://youtu.be/pzuHxL5FD5U

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  • $\begingroup$ +1, but note you won't get iron this way, but rather hydrogen nucleii and other light particles. If you've mastered fusion technology this isn't a problem, because you can just make iron out of those, while getting ridiculous amounts of energy for free in the process. $\endgroup$
    – N. Virgo
    Commented Nov 3, 2019 at 0:37
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Kinetically.

Let the star run. It is a pain in the butt to shut down and anyway it is still really hot once you do. Also it is liable to restart while you are poking around in the guts. Plus if you shut it down it stops making stuff for you. That is like cutting down an apple tree to get at the apples.

Instead, kick chunks out of the center. Here is the scheme.

  1. Identify sizable chunk of strong stuff that you don't need. A planitesimal will do.

  2. Accelerate sizable chunk to speed.

  3. Allow fast moving chunk to plow into star. It will lose material to ablation on the way in, which is why it is sizable.

  4. Solid stuff hit in the center will be ejected out, according to Newtonian physics.

  5. Catch that stuff at some distance from the star. That is the good stuff you want.

If your chunk does not kick material out of your star, try a larger chunk and greater speed and maybe a different angle, hitting the core at the edge.

For a fiction this would be extra awesome because of the weaponization potential. The aliens would scoff at the futility of trying to hit them with a giant rock they can easily dodge. The rock is instead thrown at the star...

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    $\begingroup$ No solid material can exist at the temperature of a stellar core; as one travels towards the center of a star, all you find is increasingly hot and dense plasma. $\endgroup$
    – brendan
    Commented Nov 2, 2019 at 23:34
  • $\begingroup$ @Brendan - this idea would work even better in that case, because your projectile can travel right on thru and entrain the valuable star innards in its wake. $\endgroup$
    – Willk
    Commented Nov 3, 2019 at 0:30
  • $\begingroup$ Assuming you have a projectile large and fast enough that it can travel all the way through the star, then maybe. But it seems like that projectile must be made of something at least as valuable as iron, and you're likely to lose more to ablation than you gain from the core of the star. Given that stars only have a sizeable fraction of iron (actually nikel which will decay to iron) in their cores in the hours immediately before a supernova, I'm not sure that the shock wave produced by the impactor wouldn't just blow the whole thing up anyway. $\endgroup$
    – brendan
    Commented Nov 3, 2019 at 9:33
  • $\begingroup$ Alternatively, if the impact doesn't trigger destruction of the star, then it would mix lighter elements in to the core, thus delaying the supernova. $\endgroup$
    – brendan
    Commented Nov 3, 2019 at 9:33
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    $\begingroup$ It's true that the s-process produces these elements, but they never reach high concentrations in any part of the star. The question asks about how to get the "approximately one solar mass of iron...before the star has a chance to turn into a neutron star", which is clearly talking about the iron core of a star undergoing silicon burning immediately prior to a type II supernova. If you do want to harvest s-process elements, it's probably easiest to catch them in the envelope of a late asymptotic giant branch star or a planetary nebula. Or from rocky planets and asteroids, obviously. $\endgroup$
    – brendan
    Commented Nov 3, 2019 at 21:47
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Mining a star when you want to build a Dyson sphere is the high tech version of the slapstick joke of the man sawing the branch on which he is seating.

If you mine the star you switch it off, and once the car it's off you have no power supply for your Dyson sphere.

As usual, you start mining out planets. Once you are in transhumanism you don't need barionic bodies any more.

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    $\begingroup$ I didn't intend that the Dyson sphere be built around the star that is mined out (plus, building one of those presumes you have some sort of FTL travel or species-wide patience to gather the materials in the first place). $\endgroup$
    – HAEM
    Commented Nov 2, 2019 at 12:32
  • $\begingroup$ How exactly do you switch of a star? $\endgroup$
    – TheDyingOfLight
    Commented Nov 2, 2019 at 15:18
  • $\begingroup$ @TheDyingOfLight when you get to the point where you are building Dyson spheres, a star is just a very large fusion reactor. $\endgroup$
    – HAEM
    Commented Nov 2, 2019 at 21:43
  • $\begingroup$ @HAEM I do know that, but that isn't exactly switching of a star. Just because the star/garbage is under a Dyson-sphere/my bed and noone can see it any more, doesn't meant it's is switched off/cleaned up. Switching off a star would require you to either reduce it's mass to brown dwarf level or to have a magic fusion surpression field. $\endgroup$
    – TheDyingOfLight
    Commented Nov 3, 2019 at 11:11

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