Starlifting and Opacity

There's a problem with starlifting that I hadn't really thought of before but becomes a serious issue when you consider the role of metals wrt a star's characteristics. A typical star with an average level of metallicity relies on the metals to absorb the X-rays and whatnot put out by the fusion in order to turn that energy into a more even black body spectrum. Without those metals a star turns into something fairly degenerate (subdwarfs) because most of the energy from fusion which would keep the star hot ends up being radiated away quickly as UV light.

Pretty much if you try to strip the metal out of your star you can end up turning it into something which no longer supports life and which no longer even produces enough usable energy to power your civilization. On the other hand I'm pretty sure that the masses of the terrestrial planets not including Earth are still more than large enough to create a dyson swarm that would saturate the sun's output anyway (particularly when you consider the lossiness of energy conversion and the machines using the energy).

I mean if Mercury + Venus + Mars = roughly earth's mass, and earth has enough mass to build a billion times its own surface area in habitats, and if the sun produces a billion times as much energy as falls on earth, we could find rather counterintuitively that we end up energy limited long before we run into mass limits, especially with the much higher base energy requirements of habitats relative to a planet that's held together entirely by its own gravity.

Interesting post.

Our Sun is 4.6 billion years old. It will burn about another 5 billion years or so. It burns hotter now than it did 4.6 billion years ago because stars burn hotter the older they get for the reasons you explained. Starlifting is a fountain of youth for stars. We'd want to engage in starlifting so our sun doesn't roast us in another billion years and provides utility to the earth and its inhabitants for trillion of years. The metals obtained in the process are just handy by-products.

I'm pretty sure the reason the sun and similar stars burn hotter as they get older is due to an increased concentration of easily fused deuterium. The sun won't even begin burning its helium until the core more or less runs out of hydrogen, so it's impossible for it to create any new metals or to change its opacity. Subdwarfs don't just magically turn into normal stars either for the same reason.

Much of the point of starlifting is likely gonna be to extend stellar lifetime anyway, right? Any materials coming up "the fountain of youth" in excess can simply be dropped back into the star to maintain desired opacity.

Tuning metallicity might allow us to shrink down to a red dwarf with an unnatural spectrum, though! What that spectrum looks like depends on what we look like, so speculation on that is another topic altogether, but maybe a good guess is that our preferred spectrum will be what's easiest to harvest technologically, just since a red dwarf-scale lifetime is an improbably long time for us to keep running around in meat bodies. Maybe we'll end up wanting bluer light if the longer gradient down to waste heat is better, or maybe we'll get efficient enough to slow down and sip energy from brown dwarves for an even longer lifespan, or maybe both of those at different times and a lot of steps in between.

Ook, speaking of that, a Dyson swarm over such a span is a lot of time and space for diversity to develop! It's conceivable our descendants will diverge enough that it makes sense to run two dwarves with different chemistries, though now we think of it, that does sound like it might be a lot of gravitational potential to spend energy on.