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In my world, a group of "lamplighters" seek to turn off unused stars to conserve the energy for later use. This serves a few purposes, but mainly:

  • It delays the heat-death of the Universe to some insanely distant point in the future.
  • It can be used to preserve a planet's history. For instance, if our own sun was about to become a red giant, it could be turned off as to avoid destroying Earth and all of its history.

I want to know if there is any conceivable way to stop a star from burning. Ideally, this would happen without destroying any exoplanets, but that's not a requirement. The only requirement is that a good portion of the mass is left over for later use (e.g a black hole wouldn't work for this).

For the sake of this question, let's say they have near-infinite resources at their disposal.

The only thing I can think of at the moment is smashing the star with some gigantic, dense object a few times its size. But even then, I'm not convinced it would be effective. Even if it was, slowing down something with that much mass afterwards wouldn't be easy, even accounting for near-magical technology.

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    $\begingroup$ For what it's worth, turning off the Earth's host star would kill all life on the planet and put a stop to its historical development. $\endgroup$ – Frostfyre Nov 26 '19 at 18:22
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    $\begingroup$ @Frostfyre Indeed it would. The implication is the Earth is either already uninhabitable, or all (sentient) life has already moved on a long time ago. $\endgroup$ – Nathaniel Pisarski Nov 26 '19 at 18:23
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    $\begingroup$ Make a gigantic light switch! $\endgroup$ – weakdna says reinstate monica Nov 26 '19 at 18:43
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    $\begingroup$ As much as I like the green ticks, waiting a day or so to wait for all the users to give some input before choosing an answer is advisable. I’ve no doubt some users on here would have absolutely stellar (hah) answers, but they might be asleep right now. $\endgroup$ – Joe Bloggs Nov 26 '19 at 21:10
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    $\begingroup$ The heat-death of the Universe is already in some insanely distant point in the future. $\endgroup$ – pacholik Nov 27 '19 at 10:34

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If you’re aiming to eke out the universe for as long as possible then ‘turning off’ your stars isn’t that good.

A better plan would be star lifting. This is, in effect, turning off the star by pulling all of its fuel away (Note: Only very advanced, already powerful interstellar civilisations need apply). It might help to have a Dyson swarm already at your disposal to give you enough power to lift and sequester all the yummy light elements.

Two ideas for how to do this both use whopping great magnetic fields, with the first causing stellar mass to ‘pop’ from the star in large coronal mass ejections that you can then scoop up. The second basically comprises spinning the star ever faster until it tears itself apart. Both need lots of energy, but hey, you’re turning off a star. Oh, and you’ll need to take care in your calculations that you don’t destroy whatever planet you’re looking to preserve,

Then (and this is the trick) you don’t bother turning that star back on. Make a new one. Or a series of new ones. You’ve already cracked fusion, right? Get just the planet you’re interested in and heat it with a tiny (comparatively) fusion reactor and a load of big lamps (probably more complex than that, but your civilisation can handle it!). If you properly husband the fuel from the sun you can heat one tiny little planet for a long, long time before you run out.

In the meantime the rest of the universe will freeze, but hey, who cares, right?

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    $\begingroup$ Nitpick: many starlifting methods aren't particularly complicated on the scale of other technologies that would involved in interstellar travel. We could perform starlifting on the Sun within a century or so if we really focused on the task for whatever reason. $\endgroup$ – Harabeck Nov 26 '19 at 22:10
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    $\begingroup$ @Harabeck even if we technically have the technology to do so, I very much doubt we could scale any industry to the size you would need to "lift" a star, even in tens of thousands of years. $\endgroup$ – Turksarama Nov 27 '19 at 2:47
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    $\begingroup$ @Harabeck I'd like a citation for that, too. $\endgroup$ – user76284 Nov 27 '19 at 4:54
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    $\begingroup$ If they can lift stars, they can lift planets too. Just bring the planet to another star and maybe channel the fuel from the "turned off" start to the new one, slowly, so that it doesn't burn out. All in all, nice idea! $\endgroup$ – John Hamilton Nov 27 '19 at 11:15
  • $\begingroup$ @JohnHamilton Why use stars at all? Get your fuel spinning in pre-fusion planetoids orbiting a black hole, then siphon it off to power an artificial sky as and when you need it. No energy gets wasted or even used except exactly where you want it! $\endgroup$ – Joe Bloggs Nov 27 '19 at 11:40
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In a nutshell, a star is an ongoing nuclear fusion contained by gravitational energy.

Turning off the star means stopping the fusion. That would mean either removing enough mass to remove the moderation, or freezing the mass to prevent further nuclear fusion.

Removing mass would set off the explosion of the star and also weaken the gravitation bounding with the star system, so it won't help preserving it.

Cooling the star down to the point where coulomb repulsion would overcome again the gravity push would be a better way, but won't work for preserving the star energy, since you would have to get rid of all that energy.

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  • $\begingroup$ This is a good answer. The reason I was thinking about just clobbering the star with something big is because I can't think of a great way of cooling down something like a star. I mean, even if you throw a bunch of cold stuff at it, it's just going to fuse that new matter you just gave it, right? Cooling it down wouldn't make it lose all of its energy, either. The mass that's left over after the cooling could be used in fusion at a later date, so that's all good. $\endgroup$ – Nathaniel Pisarski Nov 26 '19 at 18:36
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    $\begingroup$ @NathanielPisarski Adding more mass would just eventually create a black hole. That sort of permanently turns off the star. $\endgroup$ – Trevor Nov 26 '19 at 18:37
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    $\begingroup$ Cooling the star down is definitely not going to work. A star is held at its present size by a balance between its gas pressure and its own gravity. If you make it colder it looses gas pressure and so gets smaller. When it gets smaller its gas pressure goes up and it (usually) finds a new balance. This new balance (because the self gravity is now stronger as the star is more compact) ends up being a hotter and faster-burning star in the long run. $\endgroup$ – Dast Nov 28 '19 at 10:14
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    $\begingroup$ If you turn off the star you loose the fusion pressure which counteracts the gravity. So there are two things which could happen: first it collapses into a neutron star which somewhat defeats the purpose because it is hardly usable thereafter. Or the fusion starts again and the whole energy which was spent on cooling it down is lost. Besides that, cooling in space is really hard. Especially to cryogenic temperatures. And removing mass would make the star dimmer and longer lasting. So that's exactly the way to go. $\endgroup$ – Sekuraz Nov 28 '19 at 17:04
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    $\begingroup$ @darco Fusion is the only thing holding the star up against gravity--turn it off and it's certain to collapse into degenerate matter. So long as it doesn't go black hole it's not all lost, though. $\endgroup$ – Loren Pechtel Nov 29 '19 at 0:53
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Stars run on nuclear fusion, specifically the fusion of protium (plain hydrogen with no neutrons added) into deuterium, a process that, as far as we know, only takes place in the cores of stars (in nature). In the process, on of the fusing protons emits a positron to convert into a neutron. A more complex decay (due to more protons involved) takes place in any fusion even, whether it's deuterium-tritium, deuterium-lithium, lithium-boron, or oxygen-carbon (in the end stage of a pre-supernova collapse).

The fusion itself is governed by the strong nuclear force -- the very short-range force that overcomes electrostatic repulsion when protons get close enough together, and thus holds all nuclei heavier than protium together. The decay of one of the fused protons into a neutron is governed by the weak nuclear force, which covers essentially all radioactive decays other than fission.

If your Lamplighters had access to a method of locally suppressing the weak force, they could "turn off" decays like beta (positron or electron emission). This would result in production of helium(2) (which doesn't exist in nature) instead of deuterium, and stop the emission of much of the energy produced by protium fusion (by preventing annihilation of positrons with the abundant electrons in the stellar plasma).

Important caveat -- if the weak force suppression fails after even a second of operation while enclosing an active fusion core, it'll be very, very bad. Instead of the He(2) decays to deuterium taking place at the rate of protium fusion events, when the field drops those decays that were prevented by the weak force suppression will take place at the half-life rate of that decay. I don't have a figure for how long the half-life of the beta decay in protium fusion is, but it's short. Much shorter than the rate of fusion in an active star. That means that if/when the field drops, there will be a huge spike in beta decays in the "shouldn't exist" helions (made up word), meaning a sudden very large flux of (IIRC) 3.56 MeV gamma photons from positron/electron annihilations throughout the core of the star, resulting in sudden very rapid heating and an end effect similar to a supernova explosion.

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  • $\begingroup$ Thanks this is really helpful information. I could definitely go this route with enough hand-waving, and the explosive consequence of messing it up could really add to the tension of the fiction. $\endgroup$ – Nathaniel Pisarski Nov 26 '19 at 20:35
  • $\begingroup$ Naa .. a positron is an electron with positive charge and reversed spin - not a nucleon (core particle) like proton / neutron. $\endgroup$ – eagle275 Nov 27 '19 at 7:36
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    $\begingroup$ He-2 isn't stable - it has more energy than two protium nuclei, and spontaneously decays back into two protium nuclei. It will not accumulate. In fact, this is the major limiter of the rate of fusion in Sun-like stars - if the strong nuclear for was just a tiny bit stronger, He-2 would be stable and the Sun wouldn't last anywhere near to its currently expected (main sequence) lifetime of ten billion years. A proton in the core of the Sun has to wait on average 9 billion years before it decays into an neutron through the weak force. The rest of the chain happens pretty much instantly. $\endgroup$ – Luaan Nov 27 '19 at 10:17
  • $\begingroup$ @eagle275 Go look up "beta decay" -- it is exactly this, protons emitting positrons (to balance charge) when they switch to a neutron, or neutrons emitting an electron when they transition to a proton. It commonly results in a nucleus increasing or decreasing atomic number by one without changing atomic mass by anythign like a full Dalton. The (tiny) mass of the electron in these decays comes from strong-force binding energy, as I recall. $\endgroup$ – Zeiss Ikon Nov 27 '19 at 12:09
  • $\begingroup$ @Luaan It's been my understanding that the rate of many/most weak force decays depend strongly on the state of the nucleus. A free proton has a half life of something like 10^40 years, but in a nucleus, beta decay can have a half-life of a tiny fraction of a second. $\endgroup$ – Zeiss Ikon Nov 27 '19 at 12:11
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Freeze the star in time.

According to this https://www.quora.com/If-time-were-to-stop-suddenly-would-gravity-still-apply (Which isn't a reliable source) you could lock the explosions in time, effectively turning the star off. But the gravity would still happen, so all the planets would keep circling. Or I am reading this really wrong, but then, just handwave how it works.

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  • $\begingroup$ Once again relativity breaks my brain in half... I'm far from a physicist, but if I understand this correctly then in order to lock in time, it would just need to be moving at the speed of light, right? I'll definitely look into this and see how realistic it could be. $\endgroup$ – Nathaniel Pisarski Nov 26 '19 at 18:46
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    $\begingroup$ @NathanielPisarski might be a question for Physics SE $\endgroup$ – Trevor Nov 26 '19 at 18:48
  • $\begingroup$ @NathanielPisarski Good luck accelerating it... $\endgroup$ – Punintended Nov 26 '19 at 19:51
  • $\begingroup$ If you're going to mess with Time, just build a time-machine and ship the star off to the Far Future. Time machines are so much easier to design when you don't have to deal with passenger comfort requirements or paradoxes resulting from travelling into the past. $\endgroup$ – Alex R Nov 27 '19 at 5:34
  • $\begingroup$ curious that you base your answer on a non reliable source $\endgroup$ – L.Dutch - Reinstate Monica Nov 27 '19 at 6:31
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Break the biggest starts into smaller ones. That will require disassembly and reassembly.

The lifetime of the brightest, most massive stars is in the order of millions of years. But red dwarves might last for trillions of years (see their wiki). That is such a long time that we don't even know if protons would be stable for that long.

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    $\begingroup$ And note that this can even preserve the planetary systems (although they will be frozen.) Lift enough mass from the star to make a small red dwarf. Place it in orbit. Repeat until the whole star has been reduced to a bunch of little ones. Just be careful that the orbits you put the stars in are stable for the long term. $\endgroup$ – Loren Pechtel Nov 29 '19 at 0:56
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It's tricky.

The first stage does use an artificial Reissner–Nordström black hole, or other supermassive and robust "shaver" object. This is dropped towards the star and placed in an unstable orbit, near enough to create a workable Roche lobe inside the target star.

This allows bleeding mass off the star until it reaches the Roche vertex at the expense of both the star and the "shaver" object's angular momentum (the latter will have to be replenished using the same engines that moved it into orbit).

At the intersection of the two Roche lobes there is a saddle in the gravitational potential, and in that point the infalling mass can be diverted with comparatively little effort.

By carefully balancing the shaver's orbital parameters and using appropriate electromagnetic capture and accelerator fields, it ought to be possible to "bleed" mass off the target star and impart it enough kinetic energy to send it into a far orbit to form a "smoke ring". We will probably need a good number of "shepherd satellites" to keep the ring stable (in the picture, of Larry Niven's Smoke Ring, the main shepherd is the darker spot bottom right - Goldblatt's World).

At the same time it should be possible to bleed some of the excess thermal energy from the incoming mass to reduce the total energy expenditure (the gravitational binding energy of a star is something huge, and however we dismantle it, even with leaving the massive core in place, we will require an unholy amount of energy - the difference between the gravitational binding energy of the star and that of its remains plus the Smoke Ring).

At the same time, the mass loss will cool down the star, extending its life considerably, gradually enough not to trigger a core catastrophe. Ultimately, it might be possible to completely evacuate all fuel mass, leaving the burnt-out core alone to cool off.

In stars whose core is above the Schönberg–Chandrasekhar mass limit, the cooling off of the core (and actually the removal of too much of the fusing fuel) will trigger a core collapse, possibly accompanied by several "flashes" when the progressing collapse ignites higher-order fusion episodes in the outer envelope (helium, carbon etc.). This might present a risk to the integrity of the Smoke Ring.

Very large stars probably cannot be safely bled past a certain point; as soon as the fusion slows down, the star will begin to contract and heat up, comparatively rapidly burning through the carbon, oxygen and silicium stages. When the carbon process stops, there are less than one thousand years to a respectable supernova-like explosion. Unless somehow (more bleeding satellites?) a lot of mass is removed at great speed, easing the pressure and slowing down the collapse.

enter image description here

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In hard sci fi, what you would actually do is siphon off mass from the star and store it elsewhere (or just use it for other purposes) since smaller stars burn more slowly due to the reduced gravity (which is what drives the fusion in the first place). This is called star lifting.

The extreme end of things is to remove so much mass that the force of gravity is no longer able to support fusion and just turns into a gas giant like Jupiter, and store that excess mass somewhere else. Then you just dump all that mass back in when you want to re-ignite the star.

You should check out Isaac Arthur's YouTube video on star lifting. He discusses it for exactly the uses you mentioned, as well as other purposes. Apparently, it doesn't require any unknown physics and is mainly a matter of scale and therefore not a difficult endeavor for a civilization with infinite resources https://www.youtube.com/watch?v=pzuHxL5FD5U

But uhhhh...moving reducing that much mass might mess with your planetary orbits.

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Anti-gravity field

Fusion in a star’s core relies on gravitational pressure. You simply have to reduce the gravity/pressure to a point where fusion is no longer possible.

Of course we don’t know if it’s even theoretically possible to produce anti-gravity, but you can just hand-wave it.

In fact, anything which stops time, counters gravity or replaces the star’s core with an element which is at least as heavy as iron would work to stop fusion.

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    $\begingroup$ If you had the technology to make permanent distortions in space-time, the right topology could effectively disrupt the gravitational pressures that produce fusion while keeping the stellar matter in the same location.. say for example, a space-time "pocket" where the internal surface is wide enough to keep the hydrogen apart and gravity's effects are inverted so that mass repels mass. that'd essentially dump your star somewhere you can keep it safe until it's needed. $\endgroup$ – Ruadhan Nov 27 '19 at 11:58
  • $\begingroup$ Or create time dilation in the star, so it burns, but much more slowly... Surely this must already happen to some degree. $\endgroup$ – Harper - Reinstate Monica Nov 27 '19 at 14:36
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Slow down time for the star

One idea I've seen in some hard science fiction (especially John C. Wright's books such as The Golden Age trilogy and Superluminary) is to "put something away for the future" by orbiting it just outside the event horizon of a black hole, so that time becomes almost infinitely slowed down for that object. Then when you want it back, you use another mass to pull it up to a higher orbit and back into "normal time".

I have not the physics knowledge to explain how or whether this would work for our sun. Maybe some other answerer could flesh out this idea.

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  • $\begingroup$ Something orbiting just-outside the event horizon (actually, way above - the black hole has a lot of horizons and possible orbits are not near the event horizon) will lose gravitational energy quickly by emitting gravity waves. Not to mention the tidal forces that will tear it apart. $\endgroup$ – fraxinus Nov 27 '19 at 16:24
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You just have to realise that 85% of all stars in the universe ARE actually switched off by an unknown advanced civilisation. Physicists on earth call these switched off stars "dark matter", so you can see that its already be done ! How it works ? Who knows ? Physicists nowerdays do not even understand what "dark matter" really is, so you don't have to deal with that question, just assume it is possible to convert normal matter into dark matter and vice versa..

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  • $\begingroup$ I’m not sure this actually answers the question... $\endgroup$ – Joe Bloggs Nov 28 '19 at 0:32
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This is more of a side-remark that the lamplighters goal of keeping the universe alive most likely would not have stars as main goal:

Near-magical technology or not, in the end you'll always run against time.

This time of cause, your deadline crunch isn't the next week, but the end of the universe. But then again, the scale of your goal is on a whole other level as well.

So, let's say we want to save as many stars as possible from burning out. Then it'd only make sense for us to go after those stars, where we maximize the ratio of saved hydrogen to used effort.

It is said that we are comparatively in a young phase of the universe, and as such most stars have yet to be born. These future stars are now just a cloud of hydrogen, and as such they are easy pickings.

Not only is there no strong gravitational field that binds the mass together, you also don't need to disperse all of the hydrogen to stop a star from becoming.
All it takes is a good number of cores you disperse throughout the hydrogen cloud, each acting as the core of a future gas giant that may be close to a sun, but is not quite there.

Given that your civilization is at a very high technology level, they still might have spare time for stars burning already. Nevertheless, their main focus would be those clouds, and their doing would shape the universe.

As a bonus you'd see them only sporadically turn off a big star (and not immerse the universe in darkness, which would make them out to be an enemy of all life)

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Long story short: Spin it very quickly.

Short story Long: You want centrifugal force to overpower gravity. Although not very energy efficient, hypothetically the energy could be returned by feeding off the spin later. You'll expand the star without increasing mass, stopping fusion from proceeding further. Of course, the core, where the gravity is stronger, will pull apart last. This means the act of spinning may revert the start to dust cloud (It's a pretty large grey area between breaking the start apart and spinning fast enough to prevent fusion, and I don't know where the two are in relation to eachother, that'd take more math than I'm putting in at the moment.) But then again, a collapsing dust cloud is how to make a star, so it still works.

The hard part is doing this without adding to its mass. This can be done by shooting large masses near it in near-collision orbits. Hypothetically, it would be done to several stars at once to be worth it, each one it slingshots getting sped up.

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    $\begingroup$ Acretion is your enemy. The material will redistribute its angular momentum to the outside, radiate off the excess energy and you will quickly get a shiny new star, just like the old one. That's how the stars form in the firs place. $\endgroup$ – fraxinus Nov 28 '19 at 11:05
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I think if you wanted to stop a huge mass of elements from interacting with each other and protect the planets in the orbit. You would need to either stop time in that area or just absorb their energy completely and put a substitute mass in the star's place.

This group could create some super high tech machinery like a dyson sphere. But instead of absorbing the star this sphere will create a controlled environment where atoms wont interact with each other. And the machine will only work with the radiation from the atoms.

When they want to turn it on again they could just nuke it to kickstart the chaos inside the star.

But when a star turns off for a planet that planet gets cold, changes climates etc. so keep that in mind as well.

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Whatever is done will need to be very drastic and well beyond the realms of what humanity might achieve in the foreseeable future. Basicly its not going to happen. However if some new physics became available it might just be possible I suppose.

One way of "parking" the star so that it did not burn through all of its energy would be to cut it into pieces. The pieces would then form smaller stars or (with luck for very small stars) brown dwarves the rate of fusion would be greatly reduced. The brown dwarves could orbit each other and be reformed at an appropriate time.

Next question how do you cut up a star - I don't know – that’s where the new physics comes in. And yes I know it would be very difficult and and...

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Doesn't helium (or any heavy atoms, I suppose) poison the hydrogen fusion process? If you have near-infinite resources, you could dump helium to prevent the chain reactions from taking place.
I don't know how you'd restart a helium-poisoned sun, though. They use a divertor on tokamaks to get rid of the "ash," but whether or not something like that could be cobbled up at a stellar level might need too much handwavium.

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    $\begingroup$ I'm not an expert, but what I've been taught is that stars just prefer to fuse hydrogen. I mean, there's plenty of it around. But stars will gladly fuse Helium, and in fact all elements all the way up to about iron. I can't speak to how accurate that information is though. $\endgroup$ – Nathaniel Pisarski Nov 26 '19 at 20:33
  • $\begingroup$ @NathanielPisarski Sounds about right to me. $\endgroup$ – DKNguyen Nov 26 '19 at 22:01
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    $\begingroup$ No, they don't. Helium makes the core denser and actually accelerates the fusion (that's why main-sequence stars slowly get more and more luminous until they deplete a greater part of their core hydrogen and leave the MS). $\endgroup$ – fraxinus Nov 27 '19 at 7:47
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Squeeze It Through a Worm-Hole

Create a stable worm-hole that traverses space and time (not a new concept). Choose a worm-hole architecture that can bind to gravitational wells in space and has a fixed length in the time dimension.

Then, connect one end of the worm-hole to the center of the star now, and the other end to the center of the nearest orbiting planet at a time a few billion years into the future.

The result will be fresh nuclear fuel from the present rushing through the worm-hole and pouring onto the surface of the star's future self. Note that attaching the receiving end to an orbiting planet (rather than the star's center) is necessary to ensure the desired direction of flow, using the star's own internal pressure and gravitational potential differential to force material through the worm-hole.

Once you've mastered this basic technique, consider improving it to where it can bind to a smaller gravitational well, as that would help avoid having to destroy an entire planet each time you do this.

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  • $\begingroup$ needs sone thought on kinetic energy management, since the destination material will be moving at orbital velocity, and the source material will not. $\endgroup$ – Harper - Reinstate Monica Nov 27 '19 at 15:05
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Flood the star with COLD neutrinos (you'll need a lot of them). They will clump in the core and cool it (those that manage to interact with the star's matter will fly away). The star will become something like a white dwarf (degeneracy-supported), but cold.

Works for a rather small stars (1.4 sun masses or less), but they are a majority anyway.

p.s. you have to support the star in that state by cooling it periodically, or it will self-ignite because of the heavy radioactive elements that will tend to heat it from the inside.

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  • $\begingroup$ I'm not sure this is right. The sun isn't hot just because it's heating itself; it's hot because the more gravity condenses a given amount of fluidic material, the more that material heats up. Sure, the sun may lose some energy due to heating up neutrinos... but you're also increasing the mass of the sun. Which will condense the gas even further, causing further heat. Obligatory XKCD: what-if.xkcd.com/14 $\endgroup$ – Kevin Nov 27 '19 at 21:46
  • $\begingroup$ It may, or may be not right, depending on how much cold neutrinos interact with matter and how dense can be a "neutrino degenerate matter" in order to ensure enough cooling. Yes, the star will become a bit heavier. If the cooling works, it will "evaporate" most of those neutrinos rather quickly. The excess gravitational energy will be radiated just like any sub-star object does. $\endgroup$ – fraxinus Nov 28 '19 at 10:55

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