Taking off the upper layers of a star

[Vultur]

If the upper layers of a star were removed gradually, how would that affect the star? How much would you have to remove to kill the star's fusion?

[GrandMasterTerwynn]

If the upper layers of a star were removed gradually, how would that affect the star? How much would you have to remove to kill the star's fusion?

It would cool down and dim as you reduce pressure on the star's core. The star would contract as the radiation pressure holding up the outer layers diminishes with respect to the gravity trying to pull it in.

In order to render a star incapable of fusing hydrogen in its core, you have to remove a lot of mass. The minimum mass required for a star to be a hydrogen-fusing red dwarf is between 75 to 90 Jupiters, depending on metallicity. So for a Sun-sized star, that involves removing over 92% of that star's starting mass.

[Stark]

In Sol's case, how much mass would you have to remove to move Earth out of the habitable area in a reasonable timeframe? How quickly do the effects manifest?

[CaptainChewbacca]

If you were trying to make the earth uninhabitable, it would really be easier to just move the earth. If you managed to set up the right magnetic accelerators, using 10% of the sun's total energy output you could remove about one thirty-millionth of the sun's mass every year.

Something like that is by no means a speedy process, because even if you were using 100% of the sun's energy output, it would still take you 3 million years to reduce the mass of the sun by 1%.

[fusion]

The energy needed to remove that much mass away from the sun is crazy as you will need to have a few dozen Death Star Two blast worth of energy to complete the feat...

So might as well blow up the planet while you are at it...

[Vultur]

I wasn't talking about using it to wipe out planets, but if you were harvesting hydrogen for fusion fuel (after having used up all the gas giants).

[NetKnight]

I wasn't talking about using it to wipe out planets, but if you were harvesting hydrogen for fusion fuel (after having used up all the gas giants).

There is no point. The star itself is a fusion reactor: just build a Dyson swarm to harvest its output. Or, for that matter, just use the utterly insane power generation capabilities you'd need to harvest the stellar material to power your civilization, or better yet do both, and avoid the extra layer of inevitable inefficiencies you'd encounter in harvesting stellar material for artificial fusion reactors (the star's gravity well, if nothing else).

[Patrick Degan]

The hypothetical concept is known as starlifting. Supposedly, such methods could be use to harvest material for fusion power or more likely to manage the star's rate of fusion so as to extend it's life-cycle by billions of years.