Artificially Halting Fusion in a Star?

I had a weird thought the other day, wondering if there was a way to artificially stop fusion from occurring in a star. Staying within known science, is there a hypothetical way to do it? Maybe introducing large (really large) amounts of heavy elements that aren’t readily fusionable (fusible?)?

Adding a hugh amount of unfusible elements will not do it. That mass will eventually settle into the center of the star and the fusion will go on around it. That kind of thing already happens in stars. The helium that’s produced by fusing hydrogen is not fusible at the temperatures of most stars and it does that. Also, stars have some elements that are not fusible in their original makeup. Most of those settle in the center, although there’ll be some small amount scattered through-out that we can detect via spectroscopy.

At any rate, the total mass of the Solar System that’s not already in the sun is only a small fraction (1% roughly) of the mass of the sun, so we don’t really have a lot of mass to add to it.

The only real way I can think of to slow or stop fusion is to remove mass from the sun. Have fun doing that.

I guess we could throw a neutron star at it, not directly but close enough that its tidal force would rip apart the Sun.

There, I’ve reduced the problem down to “how do you get hold of a neutron star and move it about?”

Hey, we’d get more planets that way.

Not sure whether to say “Exercise left for the student.” or “Just a matter of engineering.” It’s one of those two.

Also the, “Then a miracle occurs” entry into the equation.

Turning off the gravity in the vicinity of the star should do the trick. It is left as an exercise for the reader to figure out a way to do this.


Can we teleport a black hole into the middle of it?

Warning: Do not try this at home.

Although a black hole may eventually absorb the star it will not halt fusion in a main sequence star. Depending on the size it might even accelerate the the CNO cycle and create novel “Hot CNO” nuclear fusion reactions that normally only occur in novae.


Invent bobbles, use lots of them.

You just need to have a Q on your side.

Heat it up more, contain it in a dyson sphere to reflect back much of the heat which would expand the star and inhibit fusion. Heat it up enough and it should overcome its own gravity and fly apart.

So, even more nonsensical than turning off gravity, eh?


Just toss the whole mess into a really big black hole. It’s the only way to be sure.

(Unless some joker comes along and turns off gravity, but hopefully by then there won’t be much left of your star, that you would recognize, anyway.)

Time travel to when it turns into a red giant ? A few billion years for our sun.

Even red giants still do fusion. You have to go all the way to when it’s a white dwarf.

BTW, you could divide our sun into 12 and a half[1] equal parts and still have fusion going on in twelve of them. The extra half would make a nice brown dwarf.
[1] and yes, I know the half is not going to be equal to the others.


Use the star’s own luminosity to lift matter off its surface. Keep doing this until the star loses enough mass to make sustained fusion impossible. This should take several billion years.

It should be possible to increase the rate of matter removal, perhaps by increasing the temperature of the star by building a big mirror to heat portions of the surface up. Alternately you could use the matter removed using the starlifting technology to power huge fusion generators, basically increasing the total luminosity of the star significantly while spreding it out over a larger volume.

If your original aim was to decrease the luminosity of the star in the short term, you will have failed dismally, since the starlifted star would shine brighter than before during this process (albeit mostly in the infra-red). But eventually you will remove enough mass to stop fusionj.

Please elaborate. Turning off gravity is not an option; reflecting light back onto the star would use real physics.

Well, first of all you cannot reflect “heat” back toward the star. Heat is a system property that reflects the amount of randomized energy contained in that system. The natural distribution of randomized energy within a system tends to level out gradients rather than magnify them. This is the second law of thermodynamics and is not subject to any kind of “engineering fix”.

Second, any non-magical material that this “dyson sphere” (I assume the poster means a uniform shell rather than Freeman Dyson’s original concept of a swarm of energy-collecting orbital satellites) will have to both accept and radiate radiation per the Stefan–Boltzmann law on both its inner and outer surfaces. Since the temperature of the incoming radiation from the star will be at a temperature greater than or equal to than the interior surface of the shell itself, the only direction to radiate the energy is outward. No, painting it silver doesn’t help other than shifting the characteristic radiative properties; it will still absorb radiation and heat up until it comes to an equilibrium temperature, and because the back side is radiating to an almost perfect blackbody at the 2.7 Kelvin microwave background, it will radiate essentially all of the incoming energy out to space. It won’t have the same spectral distribution as a star but it will radiate away at nearly the same amount of total power across the spectral distribution minus whatever energy is retained within the system up to the point that the shell melts or vaporizes away when it can no longer maintain electrochemical bonds. Again, no engineering can correct for principles of heat transfer or basic materials science.

Finally, even if you had some kind of magical shell material that was completely adiabatic (completely insulating), would remain intact at temperatures in the tens of millions degrees Kelvin, and would contain the energy being added to the system without limit, this would not result in the scenario presented by the poster (“…expand the star and inhibit fusion.”). Instead, as the temperature of the entire system goes up you would actually observe fusion occurring in layers outside the core (or rather, the area that defines the core would expand outward) and the star would experience more and hotter fusion. If the entire interior volume reached the fusion triple product (density x plasma temperature x confinement time) threshold, the entire star would be engaged in fusion with the core experiencing triple alpha process and eventually carbon burning and on up the alpha ladder.

Of course, “turning off the gravity” is absurd as well–a point I assume the reader would grasp from context, although I am sometimes guilty of failing to use my sarcastic voice–but realistically there is no way to artificially stop fusion from occurring in a star using any existing science. The o.p. asks an interesting question in a clear and straightforward way, and thus deserves a factual answer without wanton speculation masquerading as science.


So you discount the possibility of starlifting altogether? You may be correct, since there has been no evidence of such a process occuring anywhere in the Milky Way Galaxy as far as I know. But I certainly would not discount it yet.

By “starlifting” you mean somehow vacuuming up material and dispersing it? Sure, I guess if you had a really big cordless Cosmic DustBuster and a lot of time on your hands, but remember, the star is caused to fusion by the mass of its own material folding space upon it. You can’t just collect the material; you have to lift it completely out of the gravity well, and then disperse it so that it doesn’t fall back down, or add enough kinetic energy that the material achieves escape velocity, or some similarly ridiculous scheme. And if it is going to take you many billions of years to achieve this, you might as well just wait it out because eventually the star will burn off all hydrogen, turn to a white dwarf phase of helium burning, and eventually radiate all residual energy all on its own.