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Hypothesis: In application of the laws of thermodynamics (conservation of energy) it could be that the sun's energy was (almost) depleted to perform feats of magic (energy was taken from the sun).

Question: Facing an imminent supernova, how can magic save the sun from dying?

Condition: The solution should respect the law of conservation of energy.

See for answers in a SF context: How would an advanced alien race go about preventing their sun from dying?

Would there be any theories in a pure fantasy context? It does not seem feasible for a fantasy world's population to leave the world as they do not in general have the means to colonize or terraform other planets or even get there for that matter (barring teleportation magic, but if you don't know where you're going, how can you teleport there?). The sun's survival is a therefore a necessary condition for survival of such a population.

Maybe magic could be used in a more conservatory manner, but that would only delay the inevitable. Maybe an incredibly powerful wizard could transfer energy from one star to another, but this feat would surely be too much for any single (believable) wizard. Quid?

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    $\begingroup$ This question asks for how you can do something with magic, but there is no single standard definition of magic. In some worlds, the protagonists might be able to wave their hand and revert their star to its original status. In others, they might need to harness dragon's breath to collect salamander hides to coat a vessel that will be able to survive the heat and pressure of the sun so they can perform a prolonged ritual in the center of the sun to teleport excess heavy elements out of the center of the star. Overall, this winds up being a story-based question instead of something that someone $\endgroup$
    – Robert Rapplean
    Jan 14 at 21:10
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    $\begingroup$ Minor frame challenge: magic can be used to discover a new place to teleport to. There is no reason to assume that a person must have prior, direct knowledge of their destination, and no reason to assume they couldn't use magic to acquire that direct knowledge. "Scrying" is magic that shows you distant places or even times, and can often find things by mere description. "Mirror, mirror on the wall / show me the nearest habitable world for us all". $\endgroup$
    – Tom
    Jan 14 at 21:17
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    $\begingroup$ @RobertRapplean Well if you want to respect the laws of conservation of energy, as I set out in the hypothesis, you cannot simply revert the sun to its original state with the wave of a wand or any simple ritual. $\endgroup$
    – GilouLeFou
    Jan 14 at 21:20
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    $\begingroup$ Maintenance of conservation of energy actually eliminates most forms of magic, but that's a much longer discussion. Is this a sun-class star? If so, it isn't going to go supernova, it's going to turn into a red giant. If you have teleportation magic, you could open a gateway to the center of the star and give yourself a few million years by ejecting the highest pressure helium. This would also cool off the star, so you may need to find a way to compensate. $\endgroup$
    – Robert Rapplean
    Jan 15 at 1:37
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    $\begingroup$ Also a minor frame challenge - it's hard to conceive of a civilization "depleting" the sun to perform feats of magic that do not themselves destroy the world, unless there's a major efficiency gap and energy is being spent somewhere far away to make up the difference.\ $\endgroup$
    – jdunlop
    Jan 15 at 10:38

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If we're talking magic here, you can note something about the evolution of stars. When they expand into red giants and explode in a supernova, they don't actually use up their hydrogen.

The issue is that elements like helium, carbon, oxygen and neon start to built up in the core, which require more heat and energy to ignite and fuse than the star has (mass).

Stars like our sun don't fuse much past carbon, so it builds up in the core until it displaces the vital hydrogen in the area where it's hot enough and dense enough to fuse. Think of the sun being an onion, where the inner core is the innermost layer. As the fusion byproducts accumulate, it's like a rot that consumes the inside until the innermost layer is gone.

After that, there's no hydrogen at the critical mass and temperature to fuse. Sure, there's loads of hydrogen left, but it's just not hot enough.

The way to fix this is simple! To syphon the "rot" or the fusion byproducts out of the core, and fusion will resume as fresh hydrogen fills in the gap. The sun will shrink a negligible amount, and the climate might permanently get a little bit colder, but you'd probably not notice.

This sounds like a dangerously corruptive operation to try and syphon it out, you might just end up corrupted by it. Maybe building some inanimate construct that can channel that much corruptive power would make it possible.

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    $\begingroup$ I love this way of approaching it! If you would depict the byproduct as 'rot' and have magic also translate it as such to the magic users who syphon it, it introduces a very interesting dynamic for possible character development. Makes me think a bit of Robert Jordan's True Source (the male half) being corrupted and driving male casters mad. Thanks! $\endgroup$
    – GilouLeFou
    Jan 15 at 1:10
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    $\begingroup$ @GilouLeFou When I wrote it, I thought of the prison that Harry Dresden made to contain the Erlking in the Dresden Files. Sort of a structure, sort of a ritual circle, the sorcerer channeling energy into it and the construct doing the work, which would probably look spectacular and absolutely terrifying, a massive blue-white jet of plasma that pierces the sky. $\endgroup$
    – Sam Kitsune
    Jan 15 at 1:39
  • $\begingroup$ twokinds.gallery/download/art/1208/… $\endgroup$
    – Sam Kitsune
    Jan 15 at 1:39
  • $\begingroup$ But in this context, it might be better for for it to be charred black and dark red, really lean into the corruption aspect of it, even if it probably wouldn't look that way in real life. twokinds.keenspot.com/comic/526 $\endgroup$
    – Sam Kitsune
    Jan 15 at 1:39
  • $\begingroup$ If you want to offset the shrinkage and temperature changes, and assuming your magic includes very long-distance teleportation - which is probably necessary to remove the spent fuel, you could also siphon hydrogen from fresh young stars. See also @tom's answer below $\endgroup$
    – Sarah Messer
    Jan 17 at 17:19
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Rob Peter

Often, the only way to extend the life of something that is dying is to steal life from something else.

In many stories, an aging sorcerer tries to capture a young person and then sacrifice them in a magic ritual to steal their youth:

Human sacrifice under the sun

That's what I'd do here, although in this case you'll need to sacrifice something really special.

One obvious possibility would be to sacrifice a different star. That might require gathering a bunch of people who were born "under" that star and sacrificing all of them, or getting them to perform a big ritual together. Or it might require performing a ritual when the target star has reached a special position in the sky.

Another possibility would be to sacrifice something that would otherwise have an extremely long lifetime. That might be something like a Methuselah-like tree, or it could be something or someone that epitomizes a timeless concept.

Those both assume a one-time act that significantly restores their star's lifetime. There are a lot more possibilities if the idea is to pay Paul in many small installments.

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    $\begingroup$ meanwhile on Alpha Centauri Stack Exchange: "Help! An alien race is draining our star to revive its own!" $\endgroup$
    – user253751
    Jan 15 at 9:28
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    $\begingroup$ @user253751 meanwhile on Alpha Centauri Stack Exchange: our star is dying and we don't know why, "How can a magic civilization stop their sun from dying?" $\endgroup$
    – DonQuiKong
    Jan 15 at 13:26
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Give it back.

You will no doubt get some snarky comments about "magic is magic. whatever you want." Not helpful. Maybe these comments of mine will vaccinate your question against such. We will see.

But the question! Magic systems vary. Here is something I know about your magic system. /the sun's energy was (almost) depleted to perform feats of magic/

Those be some mighty feats! Whatever they were, maybe the energy is still there. Maybe those feats can be undone to return the energy to the sun?

I like this for a quest. The sun-sucking magic did not all happen at once, but over many generations of magic users. Those old timers did not know the sun was a finite resource when they performed their feats of sunsuckery. But your protagonists know now, and they must systematically undo these earlier works and replenish the sun.

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Push it Closer (or Further)

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The sun is dying. There is no getting around that. Its energy has been stolen and the Red Giant phase begins early:

enter image description here

The Sun cools and expands to gobble up the first four planets. No problem, just shove planet Earth away from the expanding star into the new habitable zone.

For conservation of energy, use magic to convert some of the Earth's mass (or Moon's mass) into kinetic energy for your giant planet-moving fart rocket.

Likely the fart rocket will take thousands and millions of years to speed up, and just as long to slow down. That is okay since the Sun expands slowly, at least on a day-to-day scale. I think.

Once the Earth is relocated, you are safe for another 12 billion years. Provided you stop leeching off the Red Sun. Stop that.

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  • $\begingroup$ Assuming the usual physics you are pretty much not safe for any number of bilions of years, the red giant phase is quite a short and intense party with alcohol, drugs and thermal pulses of 1000-fold increase of the star luminosity. $\endgroup$
    – fraxinus
    Jan 17 at 14:19
  • $\begingroup$ @fraxinus I will add it to my calendar. $\endgroup$
    – Daron
    Jan 17 at 15:14
  • $\begingroup$ I know space is big but... Is it possible you'll have to also shove Jupiter and Saturn out of the way to avoid orbit perturbations? ANd what about all those pesky asteroids? $\endgroup$
    – Nacht
    Jan 18 at 3:53
  • $\begingroup$ @Nacht We already built the Millennium Fart Rocket. Just use it to make course corrections every thousand years to avoid collisions with Jupiter and Saturn. $\endgroup$
    – Daron
    Jan 18 at 12:52
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First, if your setup is Earth-like, your magic is impressively inefficient.

You can use as little as few hours of solar energy output and completely blow the Earth into dust. Or few days worth of solar energy in order to completely evaporate the Earth.

Whatever you do on your little planet could not use up this much energy. You will get too hot just because of the waste heat (assuming working thermodynamics).

Second, stars (at least in our universe) are not this simple.

They don't burn at a constant rate until they blow. As the time passes, they become hotter and hotter and the red giant phase is approached more or less gradually.

In order to live around an aging or used-up star, you will need to take care to REDUCE its power long before the the supernova explosion.

The solution? Make gas giant planets out of it.

You will need to remove material from the star.

Since you have both magic and thermodynamics, just siphon core substance out of the star (you can suck from the upper layers as well, but removing core material will be more efficient and will make better night-sky fireworks as well).

You then clump the material in these gas planets orbiting the main star.

Done: you have younger and smaller star.

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  • $\begingroup$ Interesting theory. You could effectively say that by making the sun less massive/potent/whatever you can make it more stable and by creating gas giants, you create 'pockets of energy' that magic users could syphon from without bringing about the end of their solar system. $\endgroup$
    – GilouLeFou
    Jan 15 at 11:04
  • $\begingroup$ As I already had written in another comment, I've also been struggling with the parallel between 'energy consumption' and 'sun energy depletion' for my magic system. The idea would be that the sun would have served as a source of energy for vast amounts of time (throughout the history of the civilization). Next to that you also have the sun depleting because of natural radiation. $\endgroup$
    – GilouLeFou
    Jan 15 at 11:06
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    $\begingroup$ But you definitely make a point. Even then, in a purely fantasy context, it would be hard to fathom feats of magic being the "main" cause of energy depletion and not just an infinitesimally variation of the energy. Using the magic to pull in energy or controlling it could, however, be assumed to spend disproportionally large amounts of energy, but that would violate the law of conservation that I myself had put forward. Energy would have to be "lost" by using magic or you would have to pull in a BS scientific reason like it creates dark energy (cfr. expansion of universe). That would be too SF $\endgroup$
    – GilouLeFou
    Jan 15 at 11:08
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Arrange a deity to tell the sun it can't do this

Supernovas are actually childish behavior. Instead of shining properly, the sun would first hide and then pop up suddenly, larger, to give everyone the creeps. After popping up, it will hide again.

How to prevent this ? Just arrange a powerfull deity to make very clear to your sun its behavior is unacceptable. Don't wait too long. Stars are like cows.. if you push, they'll give in. Slowly.

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I like all the other answers but I think everyone is underestimating the amount of power involved here.

The Sun outputs 3.8 $\times$ 1026 watts. For comparison, that is like the energy output of the collision of the dinosaur killing asteroid, times a thousand, every second.

In hard sci-fi there is a scale to measure how advanced civilizations are based on their energy budget, called the Kardashev scale. Type 1 Kardashev civilizations harness all the radiation from their star reaching their planet - we're almost there. Type 2 civilizations harness the star output and with that should have a very easy time colonizing other star systems. They can spend millions or even billions of years explorung space like this. This is where your mages would be if they just captured all the energy being irradiated by the Sun.

But your mages outdid that. They managed to suck the Sun dry within the lifespan of an empire, so they are closer to Type 3 Kardashev, which should have enough of an energy budget to comfortably colonize a whole galaxy just for kicks if they so wish.

The amount of energy being used by these mages surpasses most everything you have ever seen in any media. Forget about magic missiles and fireballs; even a simple cantrip would obliterate a whole solar system with ease. It would possibly be very hard not to blow up your planet when trying any sort of evocation spell.

With such an energy budget, should the Sun not suffice, just use magic to push your planet to another yellow dwarf. Since any spell would be beyond epic, even a simple divination would show a mage where one can be found, and how to get there.

By the way, even with all this energy available, you are still orders of magnitude short of a supernova. You would need to release all the energy the Sun would ever output in its 10 billion years lifespan in a single burst to approximate a supernova.

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    $\begingroup$ I think that you should pose this as a Frame-Challenge. Also see my comment to the OP. $\endgroup$
    – RBarryYoung
    Jan 17 at 13:43
  • $\begingroup$ Don't worry SCL, the amount of magic in this world can solve energy shortages. They never used it because they were lazy. Now there's a problem and the maguses should save humanity and repent. $\endgroup$
    – Goodies
    Jan 17 at 22:51
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Put the sun to sleep

In some versions of Sleeping Beauty, the princess is cursed to prick her finger and die, but a good fairy modifies the curse so that the princess will go to sleep rather than dying.

She sleeps for 100 years, until a prince molests her, breaking the curse and restoring her and the town to wakefulness.

Do something similar.

Your people know the sun will die. So, with their last great use of magic, they put the sun into a deep sleep, only to be awakened on some distant day when the problem can be solved. As a consequence, sunlight is much dimmer, reducing even the brightest day to nothing brighter than a full moon, and use of magic is almost impossible.

In 100 years, some pampered male alien can molest the sun, awakening it and restoring light and magic to the world.

FYI: I patent dark glasses and sunscreen during that 100 year slumber. You must include this in your story.

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    $\begingroup$ that doesn't sound very comfortable for earth. $\endgroup$
    – ths
    Jan 14 at 23:29
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Stop doing whatever was draining vast amounts of energy

Clearly it was a bad idea.

Decrease gravity in the star

Cast Wingardium Leviosa on the star, and reduce the gravity. This will allow the radiation pressure to prevent a supernova.

Stir the star to maintain the optimal ratio of fusion reactions

Stars that supernova or turn into red supergiants generally still have a lot of hydrogen. If you carefully manage the output of the star you should be able to keep it going for billions of years longer.

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Since there is a law of conservation of energy which bridges the physical world and the magic world, that means that the energy from the sun that was drained via magic still exists. Perhaps the leftover energy exists as some kind of magical mana or dust in the world, or has been converted into heat (too many destructive, e.g., fireball, spells), or got pushed into a parallel dimension/realm of chaos energy. Since the conversion from magic to/from physics is fictional, it's up to you to decide how it works.

In any event, whatever energy is left behind, it's likely not longer easy to access due to thermodynamics and chaos. So the wizards are going need some kind of special magic that can gather it up, essentially reversing the flow of thermodynamics and the arrow of time. Maybe this requires an ancient, forgotten school of magic that needs to be rediscovered; or a new artifact that needs to be crafted; or help from a diety. Whatever the tool, it will end up gathering the leftover energy and putting it back into the sun. Hopefully it can be inegrated into future magic so that magic becomes sustainable.

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Stir the star so all the hydrogen gets used like red dwarfs do now. This gives you quite a bit more time and when the fuel is all used up it just goes out without a boom.

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