How to change a star's luminosity

[Ken G]

I have a question to ponder. Let's say you had unlimited access to resources, and wanted to reduce the luminosity of a main-sequence star by a factor of 2. To make it cleaner, let's take a somewhat more massive star than the Sun, so it has a shallower convection zone and the luminosity is mostly in the form of diffusing radiation in its interior. The core is fusing hydrogen via the CNO cycle, which is spectacularly temperature sensitive-- all else equal the fusion rate scales like temperature to a power like 20.

OK, so given all this, which of the following strategies would be more successful at reducing the star's luminosity by a factor of 2:
1) Insert some kind of control rods in the core that reduce the fusion rate by a factor of 2 at any given temperature and pressure
2) Insert some kind of opacity rods throughout the star that double the opacity of the gas (i.e., double the cross section per gram for scattering light).
Would either or both of these strategies work?

 

[Chronos]

Finding a material the can withstand temperatures in the surface layers, much less core, does not appear possible. So, neither option appears viable. Reducing the mass of the star is the only way I can think of to reduce its luminosity, since there is a known relationship between mass and luminosity - e.g., a star twice as luminous as the sun is 'only' about 20% more massive. Removing mass from a star would, however, be difficult and possibly destabilizing. It would probably be a lot easier to brighten up a star by feeding it.

 

[Ken G]

Finding a material the can withstand temperatures in the surface layers, much less core, does not appear possible. So, neither option appears viable.

It is a gedankenexperiment, aimed at understanding the processes that control the luminosity of main-sequence stars, in particular somewhat massive ones that don't have large convective envelopes and do have highly T-sensitive fusion.

Reducing the mass of the star is the only way I can think of to reduce its luminosity, since there is a known relationship between mass and luminosity - e.g., a star twice as luminous as the sun is 'only' about 20% more massive.

Yes, changing the mass would certainly work. But let's say you only had the two options I presented, and you did have the capability to follow either course. Which do you think would work, or neither, or both?

 

[Chronos]

I don't think you could stabilize the star at half its luminosity by either method. Gravity appears to be the fundamental force driving luminosity of a main sequence star.

 

[Ken G]

But a main sequence star does in fact have a fusion rate, and an opacity. Are you saying that if the rate of fusion, given some density and temperature, had just happened to be half as great as it is, stars would not be stable? Or if the opacity were double what it is? What I'm asking is, had either of those been true, what would be the luminosity of the perfectly stable star that has a mass a bit higher than the Sun? Would the luminosity be about half in both cases, or only in one case, or neither case?