# What would be the most efficient and cost effective way to stop a star's nuclear fusion ('kill it')?

I want a group of freelancers on a spaceship to stop a star from functioning. No government funding and they have to get creative. What would be the cheapest way for them to achieve this? I know we are talking about a STAR and I could just throw a black hole or another star nearby or whatever, but I want something clever. A plausible futuristic tech that can get the job done (maybe draining, flinging a meteor with a shitload of iron into the heart of it) with a bit of engineering ingenuity. It doesn't have to be drastic; it can even take a couple of years.

They also have to do it discreetly, (no violent explosions).

I'm all ears!

• Comments are not for extended discussion; this conversation has been moved to chat.
– L.Dutch
Dec 10 '20 at 13:37
• The SG-1 team accidentally sent a star heading towards destruction; the Asgard had to fix it for them. That's a form of acceptable handwavium. Dec 10 '20 at 17:31
• @JANXOL, en.wikipedia.org/wiki/Sun#Photons_and_neutrinos It says that it takes between ten thousand years and 170 thousand years "for radiation [from the core] to reach the Sun's surface*" It says, that if you could switch off nuclear fusion, it would take thirty million years for the Sun to settle down to a new stable state. I think it very reasonable to think that it might take a century or so before we noticed a change in the Sun's surface temperature. Dec 11 '20 at 16:53
• * The article says that the mean free path for photons in the Sun's core and "radiative zone" is on the order of one millimeter. Dec 11 '20 at 16:55
• @SolomonSlow How soon would we see the difference? Well, the Neutrino detectors would suddenly go very quiet. But there would be zero visible change so they would blame something other than "the sun has gone out", which they have been doing, somewhat, ever since those detectors came online. en.wikipedia.org/wiki/Solar_neutrino_problem Jan 2 '21 at 14:14

Stars are ridiculously large, on a human scale. Heck, if every nation on Earth banded together today to try to stop the sun from working we probably couldn't do it. This comes from what stars are: a great big pile of hydrogen and helium, so much that the force of gravity starts overcoming the electrostatic repulsion between the atoms and they start to fuse. Fusion is such a fundamental process that nothing short of turning the whole star to iron or disintegrating it and scattering it across the galaxy will stop it. If you have a star-sized pile of light elements, there will be fusion.

I don't think any of the things you proposed would work. Bringing another star or black hole nearby is not discrete, would destroy the Earth, and is essentially piling more mass into the star. Might succeed in messing it up, but noone would be around to care. Plus if you can move around stars and black holes you could just move the star somewhere else.

Draining would be... difficult. Sure, if you took away enough of the star's mass it would stop the fusion, but where are you putting that mass? And how are you moving it?

As for throwing a meteor made of iron into the star, well, nothing would change. The sun outweighs the largest asteroids by a dozen orders of magnitude. They could fall into the sun and it mostly wouldn't notice. Even if it were made entirely out of iron, there's already several planets' worth of iron in the sun, and it doesn't really care.

Stars are ridiculously beyond human control, at this point. Heck, we can't even control a planet. So the solution might have to be from a different angle.

While we can't stop a star from working, you might be able to trick people into thinking it, which is a much lower-budget (and more feasible) task. If you want to prevent solar energy from reaching a given planet, you can fill its orbit with junk to block the light. This already sort-of happens---the year without a summer is a parallel example. If you put enough stuff into orbit, you would also trigger Kessler Syndrome, so it would be hard to fight back against.

TLDR: It's not going to be possible to put out a star. But you can fake it on a lower budget.

• Stick a big parasol in space at the right point and boom: star’s out. Do it right and you could probably use the star’s own radiation pressure for station keeping. Dec 7 '20 at 18:50
• "Heck, if every nation on Earth banded together today to try to stop the sun from working we probably couldn't do it." I'd go with "definitely" over "probably". Snuffing out a star requires either moving astronomical (hah) masses, or magic. Dec 8 '20 at 1:13
• If you want a more complete and expensive "fake" solution, you can construct a Dyson Sphere around the star. It would still be orders of magnitude cheaper and more feasible than killing the star. Dec 8 '20 at 5:48
• "Heck, if every nation on Earth banded together today to try to stop the sun from working we probably couldn't do it." — Yes, and it’s about as far out of our reach as a neolithic chieftain saying “Even if all the strongest warriors in the village banded together to try to drain the Atlantic Ocean, we probably couldn’t do it.” Dec 8 '20 at 11:10
• People are so willing and able to be hoodwinked that you need not actually change anything physical to convince them the sun is dying. It should take nothing more than repeated lies. Dec 8 '20 at 20:55

# Strangelets

Your tags are science-fiction but not science-based or reality-check or hard-science, so let's get speculative!

Strange matter is matter with equal proportion of strange quarks to other quarks. Its most notable characteristic (at the subatomic level) is that unlike nuclear matter, it is comprised of a soup of quarks, rather than more discrete subatomic particles. This gives it no effective electrostatic charge, so it can get very dense because gravitational attraction overrides the (nonexistent) electrostatic repulsion.

Now, why does this matter to your would-be sun-snuffers? Because there is a theory (with no solid proof one way or another) that nuclear matter - the matter that makes up the nucleus of ordinary matter - is metastable with strange matter, and that contact with strange matter could catalyze a reaction transforming regular matter into strange matter, with the concurrent destructive effects to... everything that's used to being made of normal matter. This is unproven (and in fact, unlikely, because we've seen no evidence of the stuff existing), but we're being speculative and presumably your universe has FTL transport so we're already bending the rules of physics.

So, your freelancers, using the Witherspoon Device (her great-great-great-grandaughter, thank you for asking), create a strangelet, held in a gravimetric field. They then propel this at the star in a specialized torpedo casing that contains a power source sufficient to bring the strangelet into contact with the chromosphere. (How? Who knows?)

Because the strangelet is being helped into contact with the sun's matter, rather than being blown away by the solar wind and radiative pressure, it actually starts the conversion of part of the chromosphere into strange matter, which starts to collapse. This process will take a while, but will eventually kill the star.

Possible downside (don't know if this matters to your freelancers), as the core of the star rapidly gets denser, you will probably trigger a type-B supernova, as the gravitational attraction causes an early core collapse.

Almost all of this is certainly nonsense, but it's more plausible than hauling a black hole around or siphoning off half a stellar mass of... mass, and flinging it somewhere else.

• Addendum: one of the concerns people had about the LHC was that it would make strangelets. It hasn't, and if it did, all indications are that they would decay into a ground state that is electrostatically charged and would therefore be kept away from normal matter until it had further decayed. The idea that nuclear matter is metastable is also rampant speculation. Dec 8 '20 at 1:32
• I considered strange matter, but figured it would violate the requirement that you not have a big explosion. Dec 8 '20 at 1:35
• @DWKraus - yep, just noticed that in the OP. I like my answer anyway, because it appears to have the least energy cost (aside potentially from the magical FTL drive solution), but I imagine a supernova would qualify as "a big explosion". Dec 8 '20 at 1:36
• What makes you believe that a strange star wouldn't emit EM radiation just like a star? Dec 8 '20 at 5:49
• @MolbOrg - I didn't use it wrong. Strangelets are speculative, but not pseudo-science. They're a weird, theorized form of matter. Dec 10 '20 at 21:40

The Mass Problem

The Sun is 99% of the Matter in the Solar System. This should be true for most Solar Systems. An exception would be very small Stars but even then, they are big.

This means that there is physically not enough Matter in the rest of your Solar System to do anything except make the star burn a tiny bit hotter.

More Problems

As a matter of fact, dumping stuff into the Star will only make it hotter and burn more violent.

El solution

In order to stop the Fusion inside the Core, you need to make the Star lighter. Because Gravity is the cause behind the Fusion in the first place. Thus if you take away the Mass, the Fusion process stops at some point.

How you would do that in non Astronomical Timelines is beyond me. Even if you could somehow remove one Earth worth of Mass each day, it would stil ltake over 900 Years.

But sure, if time is non of your concern, building a Strcutre that can extract 1 Earth worht of Mass a day and launch it into an Orbit will get the Job done. In 900 Years.

• Dec 10 '20 at 20:08
• Lmao, just do it, aint that hard xD Dec 10 '20 at 20:14

## Plausible-sounding Handwavium:

I'm not sure if there IS a good science-based answer to this, so here's as close as I can get.

In the novel The Mote is God's Eye, aliens are trapped on their home world, even though there's a wormhole to another star. The wormhole opens INSIDE the other star, and the alien's shields grow the more energy they're exposed to. Their ships arrive at the star, the shields grow exponentially until they overload, and BAM. Human shields can't absorb energy, so they fly to the wormhole with a shield strong enough to keep out the star's energy. No bam.

I don't know what kind of handwavium tech is available in your world, but here's my suggestion. A shield that powers itself by absorbing energy exists. It doesn't have to be the normal thing (maybe it burns itself out in seconds and isn't useful for real-world applications, or they have a broken one that works this way).

Second, whatever FTL you have needs more power to go further, and to make the FTL field bigger. They have access to a large derelict ship with a jump drive, and install a self-charging shield into it. The whole thing is rigged to feed the power from the shield into the jump drive and expand the field size to a truly vast size. There can be dramatic short-cuts (like a 'bad' jump shifts things into parallel/alternate universes, or disperses mass across the galaxy - whatever) but the goal here is to shift enough mass of the star elsewhere so it is either gone or goes out.

No one uses this for any practical reason. Trying to power a jump this way will (at best) teleport you halfway across the universe to a random location. Only for your band of star-saboteurs, the more random the better.

• The human shields do absorb energy, they just don't expand (increasing surface area) when they do it. The expansion is an improvement in normal space combat (larger surface area to radiate away that absorbed energy), and just happens to be worse when you're inside a star ... Dec 8 '20 at 12:38
• @Useless Thank you, it's been years since I read it. Dec 8 '20 at 21:07
• Me too, it's funny the little details that stick with you ... Dec 8 '20 at 21:50
• Thanks for actually understanding what I asked and also for the detailed answer Dec 9 '20 at 23:48

There are various ways to do that depending on the technology level.

1. Spaceships use Alcubierre Drive: Your freelancers modify the space-time contracting tech used in the Drives to fold the space around the star or black hole.

Why this hasn't been tried before: Programming the Drives to fold such a huge region is ridiculously complicated and beyond the capabilities of super-quantum computers of that period. But your genius freelancers have found out a way.

2. Spaceships use Wormhole Drives: Your freelancers create numerous wormholes inside the star to drain away it's elemental fuel.

Why this hasn't been tried before: Calculations to position the wormholes inside stars are ridiculously complex. And it possible to create only one wormhole at a time for a very small duration due to energy and technological limitations. But your freelancers found a way by somehow using the energy of the sun itself to keep the holes open.

3. Normal reaction drive with a Highly Advanced Portable Particle Collider on board(HAPPC):

A) Your freelancers modify the HAPPC and put it in the orbit of the star. When the HAPPC is behind the star so that Earth cannot see it, it spits out anti-matter, which slowly eats up the star. It does this by using solar energy to create matter and anti-matter through pair production. The matter created while creating antimatter would be used to power the HAPPC by nuclear fusion.

Why this hasn't been tried before: Because only your team was able the create a portable particle super collider.

Note: I really liked part A of HAPPC but the physics is a bit shaky here.

B) Your freelancers use the HAPPC to create exotic element and compounds using elementary particles other than up, down and electrons. These exotic compounds somehow eats away the star.

Why this hasn't been tried before: Because only your team was able the create a portable particle super collider and were smart enough to be able to create stable exotic elements and compounds.

• The HAPPC wouldn't work. While anti-matter can annihilate with its matter counter parts, it won't just vanish into thin air, but create other particles, which will react further. But disregarding that, the sun is so extremely large, that even if the anti-matter annihilation would work as intended, it would take super long to actually do something. With current earth tech, we managed to trap 309 anti-hydrogen atoms! ATOMS. Assuming you can shoot 300 anti atoms per second into the sun and they all react in super optimal conditions, it would take 9.5 * 10^46 years to annihilate everything. Dec 9 '20 at 11:59
• @infinitezero 1st argument: We can use the matter created while creating anti-matter to run the HAPPC by fusion. 2nd argument: Yes but that's why its HAPPC. Dec 9 '20 at 12:47
• @AlphaDelta pretty sure that violates conservation of energy. Dec 11 '20 at 0:35
• @JoannaMarietti yeah, looks like I overlooked a few things. Give me a day to think a way around and if I fail, I'll remove part A of HAPPC. Dec 11 '20 at 6:30

As we do not have the technology of a class 3 civilization, it would not be necessarily productive for us to speculate on the comparative energy efficiencies of how to carry this out. However a class 3 civilization no longer cares about energy expenditures as they have access to extremely high power sources, so I would only consider time efficiency. I will list some high-level options, and you can decide what sort of technology or real physical processes (such as removal of mass by a nearby singularity) may be used to carry them out. I would choose the last option listed in the explanation below: a device that changes fundamental physical constants in a localized region of spacetime, as this would stop fusion instantly, but only as long as the effects of the device persist (unless the device changes the constants permanently, in which case you had better put some warning buoys in place!).

I have a background in physics and can say with certainty that only a class 3 civilization could accomplish this. This would be done by modulating a star's classification (and thereby what, and whether it can, fuse via any of the known processes of stellar nucleosynthesis) by adjusting its mass and its elemental makeup. Here is how you might go about doing so:

• If you want to stop fusion by adding mass, then add a lot of mass, consisting of an element which a star of the resulting classification cannot fuse, to the star. This would trigger a nova, which may need to be contained to avoid undesired consequences.
• If you wish to stop fusion by removing mass, then you have two options that I can see. 1) Remove enough fusable mass of the particular element(s) that a star of that classification can fuse. 2) Remove dark matter only in order to reduce gravity. Both of these options may trigger a nova by changing the classification of the star unless you also take care to remove enough mass so that the star reverts to being a gas giant as it was before it developed enough mass for its gravity to apply enough pressure at the core to overcome nuclear forces, which is the condition that is required to trigger stellar nucleosynthesis.
• If you wish to neither add nor remove mass, then you could hypothetically create a localized area of spacetime, which envelops only the star, in which one or more of the fundamental physical constants of the universe are different, with the aim of stopping fusion, such as by turning the star into a neutron star. NIST has a complete list of fundamental physical constants. I would advise that the author not speculate at what value the fundamental constant(s) should be changed unless they have access to someone with a strong mathematical background in nuclear physics. However, perhaps the constant(s) that could plausibly be modified are the Newtonian gravitational constant G (which would change the amount of gravity that mass exerts thereby increasing the threshold for fusion to start as the atoms at the stellar core are under less pressure), or Plank's constant h (which changes the strength of the nuclear forces that must be overcome to begin fusion). You could even change the value of pi to get the result, but I wouldn't even begin to speculate on the other consequences within that localized envelop. Pi is a mathematical constant but it has been speculated in some multiverse theories that all constants may vary between universes. A sufficiently advanced class 3 civilization could possibly have access to such a device, if such a device was even possible.
• I was thinking of Q's solution, "just charge the gravitational constant". However, instead of gravity, what about making the nuclear force a little weaker and Coulomb force a little stronger? Then there's less energy in the fusion reaction. Less energy means the star contracts. Take it far enough and it will contract into a neutron star. Then you can put the laws of physics back to normal and it will be stable. Dec 8 '20 at 21:44
• @Schwern Sure, changing fundamental constants to turn the star into a neutron star will also achieve the goal of stopping fusion. I don't think it's useful here to speculate on which constants should be changed. I have a background in quantum mechanics (upon which nuclear physics is based) and I can tell you that changing one will have vast consequences and would require supercomputer simulations to determine the overall effect on the cosmological scale. And that wouldn't even cover dark matter, dark energy, and other things that our current models do not account for. Dec 8 '20 at 23:04
• This needs some quite efficient engine on your steering planet, so it doesn't run out of fuel (i.e. out of planet) too fast. Dec 9 '20 at 0:32
• I can kinda see a trend here of useful answers not being upvoted but ones that give lecture on how stars work are xdd It's an interesting idea to modify a fundamental rule in a localized area, I haven't thought about it. Thanks a lot Dec 9 '20 at 23:52

There's is only a single semi-plausible way to do this, but it requires a handy stellar sized black hole near by, plus a planet sized object with a ridiculously efficient drive attached, so that you are able to move this planet around. Here's how to do it:

1. Move the planet next to the black hole to entice it to move into the direction you want. You will go into an offset orbit in front of the black hole to accelerate into that direction, firing your engine all the time taking care that its exhaust plume does not hit the black hole.

2. Using the planet as a drive to move the black hole, put the black hole on a direct collision course with the sun.

3. Once you enter the sun's gravity well, you need to flip around to the rear of the black hole, accelerating it away from the sun. You need to reduce its speed at least beneath its escape velocity from the sun, binding it gravitationally to the sun.

4. Keep decelerating the black hole for as long as you dare.

5. Fire your engines to get out of the solar system, fast.

What will happen next is this:

1. The black hole has a rather tiny diameter of around 30km, and it will hit the sun with a speed slightly below its escape velocity. As it enters the sun there will be a flash of gamma rays. After that, nothing happens until the black hole emerges on the other side, producing a second gamma ray flash.

2. Since the black hole is now bound to the sun gravitationally, it will rise to quite a significant height (several astronomical units, probably) before it starts falling back down, repeating the above.

3. Since the black hole scoops up a tiny fraction of the sun's mass on each pass through its core, it slowly increases in size and looses velocity. The reduced velocity reduces the height to which the black hole rises in each cycle and increases the frequency of the cycle.

4. Since there is now a second stellar sized body in the solar system, the orbits of all the planet will become unstable, and the planets will be flung out of the system over the course of a few orbits. This will be the effect that ends all life on earth.

5. The black hole produces gigantic amounts of heat in the sun's material on each pass through it. In the long run, this increases the core temperature and causes it to expand. This will take a long time to propagate towards the sun's surface, but when it does, the sun will get much hotter and increase in size.

6. As the core's density drops, the sun's fusion stops. However, the sun + black hole system will now be producing much more heat than the sun ever did. The sun keeps getting brighter, hotter, and bigger.

7. The immense heat increases the solar wind to insane levels. This will cause the sun to eventually loose more matter to the solar wind than it looses to the black hole.

8. Still a long time later, all the sun's matter is either consumed by the black hole, or blown away from it. The black hole will remain, having only ingested a small part of the sun's matter.

This whole drama would unfold over the course of many years and centuries, so I guess, it's worthless for your story. Nevertheless, it's the only fully hard scifi method of stopping a star's fusion that I could think of, so I guess, it's both a correct and useful answer to your question.

If there are freelancers, and they want to stop a particular star, then they have access to certain resources that already violate a bit of the science we know of in the universe. They probably at-least have access to faster-than-light drives, and some form of auxiliary shielding. Luckily, that's almost all they need to give it a good attempt.

## The Plan

The freelancers get a few spare ships, and refit them together. Importantly, they use two FTL drives, massive capacitors, and the strongest per-surface-area shielding ever made. This requires stripping everything else from the ships, including the power supply, so they can minimize the surface area needed for shielding.

With everything in place, they charge up the capacitors and set the first FTL to send it directly into the center of the target star. At the instant it exits, it unloads the stored energy in the capacitors through the shields, pushing as much of the star away as possible. It also needs to immediately engage the second FTL drive, taking the star with it.

Now, with how FTL drives work, the freelancers aren't sure of this plan's effectiveness. Theoretically, the math works out to give the FTL long enough to start the jump, destroying almost every other component on board. However, FTL drives are notoriously inaccurate and unreliable, and almost never work on the first attempt. It might explain why no one has heard of a plan like this having ever worked.

• Hello Wesley, welcome to Worldbuilding! I'm gonna give you +1 just for using the reality that we don't have any idea how FTL works as an actual strength in your answer substantiation why no one has thought of the idea before. I love it! When you have a moment, please take our tour and read through the first two bullets of our help center to get an idea of how the site works. Cheers! Dec 8 '20 at 1:23

Realistically, there are only two ways to put out a star, neither are remotely within our capability:

1. Take it apart. You can carefully put it back together afterwards but beware that the result is a white dwarf with a huge amount of hydrogen--if a fusion burn ever starts it will result in a cataclysmic explosion--the normal temperature regulation does not work in degenerate matter. Note that the energy requirements will take a K2 civilization far, far longer than you allotted.

2. Take away it's energy. We don't even have any idea of how to go about this, and note now we have the reverse problem--getting rid of energy far beyond what a K2 civilization works with. Once again, you end up with a degenerate body full of hydrogen.

They have FTL, so they can bend gravity and time. They can use either one:

• Gravitationally "levitate" the inner mantle. This has two effects: It reduces the pressure on the core so that fusion stops; and it keeps the star from collapsing (which it would normally do once the radiation pressure is gone). Problem: The core resembles us a little too much — now the pressure is gone it really wants to relax and push its boundaries, and it needs to if we want to stop fusion. Your rascals will need to find some relief measures, perhaps by siphoning off a substantial share of it "elsewhere" through a convenient wormhole. There is one disadvantage: That fusion has stopped in the core will take some time until it becomes noticeable on the surface — estimates for the order of magnitude for the time range from 103 to 106 years.
• It is perhaps more elegant to use time, not gravitation, because they can slow down cause and effect at the same time, and the effect would be immediate. They simply slow time down for the entire star, reducing the rate of fusion and lowering the energy output both in terms of intensity and wavelength.

The way it was done in one of the Revelation Space books is:

Highly intelligent self-replicating machines "contaminated" a Jupiter-like gas giant in the system, and over a few years they replicated at incredibly fast rate, and used the planet mass to bootstrap a heavy high tech industry, which itself used the whole planet mass to build a giant handwavium star killing machine, which tore open a hole (gravitational? magnetic? I don't remember) in the outer layers of the star, leaking highly pressurized core matter in a solar system-sized death plasma jet, that itself was aimed at the planets and used to sterilize all life in the system. If you maintain the weapon powered long enough (decades? centuries?) and enough matter escapes, the star will lose its ability to fusion.

Sure the whole process goes largely unexplained and relies on fictional physics, but at least the scales involved are more scientifically plausible than "tossing a drop of red matter into the sun".

As far as I know, a star generally 'die' when it runs out of fuel and the core collapses, turning it into a supernova and later into a neutron star and/or black hole.

A core collapse generally means gravity shifting inwards (super nova/neutron star) or outwards (slow cooling off and eventual black hole). Depending on your technology level (does gravity changing technologies work that can cause an imbalance in the core? wormholes that can siphon off the fuel?) there may be things that can be upscaled to work with stars. But even then, this will take many, many years/millennia/even longer to actually happen.

But perhaps it doesn't need to die completely? Just a "minor" change could make the system unviable for habitation in the long term - large physical bodies causing solar eruptions and thus radiation; gas giants starting to interact with each other which might end with them turning into a sun of their own etc.

Perhaps just the threat of it turning supernova/neutron star/black hole/new star in the next thousand/million years is enough to cause people to abandon the system, as they know the process will basically make the system unviable for habitation due to extreme radiation waves.

I would look into some kind of butterfly effect; some kind of 'near-miss' scenario that could be altered. For example, a small collision with an asteroid changes it path, causing it to crash into two others in the asteroid belt, which collide with four more, etc. Your star system will in a few years be travelling near this huge band of asteroids orbiting another system, but instead of passing near it, they are suddenly in the path of the shower produced by this collision, which will pelt the system, including its star, showering the system with asteroid impacts and radiation from solar flares, and possibly toppling the precarious balance of its almost-unstable star.

Of course, this would need a massive cartography exploration of the asteroids; your freelancers could be going there undercover as an expedition to evaluate the rocks for rare commodities unavailable in the system, do the math required to put the rocks on the 'right' path and make that happen, then come back to warn the population, possibly turning themselves into heroes.

Create a small device that will be in a close orbit to the star. This device will be powered by sunlight. It captures stellar wind particles leaving the star and converts them to matter. This matter is used to build another device just like itself. It also converts some of the stellar wind into a large block of lithium. Since the device makes copies of itself, the number of devices increase exponentially. When each new device is created, it is placed in the same orbit as it's parent. Over time, the star loses mass and the ring of devices gains mass. This causes more hydrogen and stellar wind to escape at a continuously faster rate. Eventually, the mass of the entire star is converted into devices and blocks of lithium that are all circling the same center of gravity that the original star had. The process runs out of solar energy when the star shrinks to the size of Jupiter. The inhabitants of the planet are horrified as the star slowly turns dark.

• "Eventually" - 5-10billion years later .... Dec 10 '20 at 21:41
• the star loses mass at exactly the same rate as normal, if you just capture the stellar wind.
– ths
Dec 11 '20 at 1:20
• I admit, I stole this plot from the movie "2010 The Year We Make Contact" But in the 2010 movie, it's Jupiter that's affected. Dec 13 '20 at 3:06

Spin the star up until it breaks apart.

First add a device to the nearest planet to the star that is designed to make the planet rotate (I assume spinning up a planet is slightly easier to achieve than directly trying to spin up the star). As the planet will no longer be tidally locked to the star, it will induce tides inside the star (and probably the planet, so this planet may turn into lump of molten metal but as long as you can keep it confined and spinning all is good). You will also need to alter the planets orbit to bring it closer to the star, so maybe add some shields to the planet as well for good measure. As the tidal forces increase the star will start spinning, get it spinning faster enough and it can reach a critical rotation rate where the outer layers are ejected (the surface has a velocity greater than a the keplerain orbital velocity).

As the star loses material eventually you will reach a point where nuclear fusion no longer occurs and thus the star is no longer burning.

• Only requires around 10^41 joules or so, which makes this one of the more plausible answers. But still, for the sun, it looks like that equates to a few million years' worth of its fusion energy output. Dec 12 '20 at 23:35

upsie, I missed that bit - They also have to do it discreetly, (no violent explosions). yeah, probably have to delete this answer ....

it can even take a couple of years.

okay, now u made everything hard for everyone, and there are some interesting answers if we stay in sci-fy, but to add to the pool

what won't work

first of all, short on what won't work - adding matter on top of a star to change the ratio of elements to extinguish reaction won't work on timeframes of 100'000's of years. The reason for that is the core of a star, as matter does not move(mix) there that freely because of the density of it, and time mentioned is the time needed for energy to leave the core, so I guess it even worse for the matter to go in and redistribute. handwavium makes everything possible so keeping that in mind it can be a plot by itself.

Star dissassembler "Supernovae phuff 9000"

works in a similar way as to blow something to extinguish a fire.

There is such a thing as Muon-catalyzed fusion it makes fusion go faster mixing in particles which are similar to electrons by charge but more massive and when they orbit hydrogen it makes the effective size of such atom significantly smaller, thus improving reaction by kinda "reducing" repulsion force.

At least two pieces of handwavium needed - produce enough of muons and the second one to deliver them where they need to be, to the core.

The first one is lesser - energy produced by the star may suffice and as catalyst proportions, one does not necessarily need that many of them.

The second one probably as hard as mixing matter and complexity reduced just by 2-3-5 orders of magnitude because particles are smaller and fewer in numbers.

Getting to the core at concentrations 1 ppm or 1 ppb or 1 ppt or even in smaller cooncentratios they affect core bringing it to supernovae conditions, but u control the force or strength of its phuff by how much muons added in there.

Type Ia supernova produces about 1–2×1044 J in its blast, and for a star like sun u need something like 1/1000 of it, something on a scale of 2×1041 J or less as it about total binding energy of the star, but u need the stuff to stay in the system(so less energy) and just spit in chunks size of Jupiter, again less energy required overall.

A valid hole in the plot to be aware of is the question - if they have Muon-catalyzed fusion capabilities and are significantly more technologically advanced than the technology of today why not dismantle star directly. it is not clear cut and there can be many answers to it - why not, but it is indeed possible to be direct and dismantle a star, by as an example elevating the problem of delivering muons to the core directly and apply a pealing layer by layer approach in accordance of how deep in one can deliver those muons. or by throwing a few other legit(kinda) technologies to accompany the process and which can be stated conducted and managed by a small crew of people and not being them k1,k2,k3 civilizations by themselves. explanations are rather long and not clear but as it is related to those methods there are 2 relevant old answers of mine 1, 2 - so as u may look for other answers over there for inspirations and generally on wb as star engenering isn't a fresh topic here, mean a/q's do happen on that subject.