My first post here, and it's more about destroying worlds than making them.

Consider this scenario:

An earthlike planet where a powerful magic spell has been cast, protecting all positrons from annihilation on contact with regular matter. Stable antimatter can finally exist (in a sense). And positronium finds itself an array of useful applications, including weapons exchanges with parallel universes (which don't share the same protective field).

Something these wizards failed to account for was this protective field expanding outwards at the speed of light. 7 minutes after the spell was cast, positrons began to build up in the planet's sunlike star. The proton-proton fusion reaction at its core becomes about 5% less energetic, as it was fuelled in part by electron-positron annihilation. This goes wholly unnoticed for a while due to the 1000-year half life it takes for heat to reach the sun's surface.

Some time later, let's say 10,000 years, a terrorist group called the Curse Breakers disables the spell. All stored positronium detonates immediately. But 14 minutes later, the survivors of this blast bear witness an even greater cosmic catastrophe - the destruction of their sun.

What I'm asking is this: how big a boom would there be? How fast would it happen?

If my calculations are correct, the thick shell of positrons around the core would contain 6.28x10^36 joules. With this energy released in a tiny fraction of a second, could the star undergo a helium flash? Runaway fusion at its core? Maybe even a supernova?

(If not, how long would the spell need to last to generate enough positrons?)

Edit: And what effects would be felt on the planet, assuming it is earthlike and orbits at 1 AU?

  • Welcome to worldbuilding.SE! This is a good question, but I wonder if it would be better received if we backed away from some data and included others. The nature of the explosion is irrelevant, the actual joule count is, too. The ratio of the explosive energy to something is important, but what is that something? Rather than saying "positron shell," could you refer to a specific layer of the sun? such as the Photosphere or Corona? Doing this would avoid what I suspect will be a series of comments trying to align your description with science rather than answering the question. – JBH Jan 6 at 19:26
  • Well, the short answer is that I was hoping you could tell me. Whether the positrons remain around the core, diffuse into the upper atmosphere, or are sprayed out as solar wind raining fiery death down on every nearby planet is mere speculation on my part. I imagine some might pair with electrons and become neutral positronium, which could float to the surface due to its low density. But does buoyancy even work the same in a star's atmosphere? – Jynto Jan 6 at 19:29
  • The type of star matters greatly also what would you classify as the destruction of a star. A nova is actually a contraction of the star under its own gravity fusing most left over hydrogen while emitting a flash of light. This is almost the opposite of an explosion. Due to the size of our sun it will never go into a nova but first expand and than collapse, at what point in this cycle would you call it destroyed. – D.J. Klomp Jan 6 at 19:33
  • In the title, you say "the sun"; but in the body, you talk about the star of a different, alien system. Please specify what type of star you have in mind, its size, etc. If you want to keep it simple, you could just state that it's identical to our Sun; if you already have something else in mind, then specify the data for the star in question. – a CVn Jan 6 at 20:01
  • To clarify, it is a sunlike star. (It would have been simpler actually if I just said it took place on Earth, but for the fact that I'm stubbornly refusing to contradict my own multiverse lore!) – Jynto Jan 6 at 21:38

For comparison consider a helium flash, when a sun-like star has aged a bit, it will develop a core of degenerate helium. The temperature is not enough for this core to start nuclear fusion. However, the temperature will gradually rise until it is hot enough for the helium to start to fuse. Becuase the helium core is degenerate, the helium fusing is not thermally regulated, and all the helium fuses in a few minutes called a helium flash.

A helium flash releases about $10^{41}$ Joules almost instantaneously. However, the energy released by this explosion causes the core to come out of degeneracy and thermally expand. Nearly all of the energy is absorbed by the expansion of the core, and the outer layers of the star. The Helium flash is almost undetectable from outside the star.

Your explosion releases only 1/10000 of the energy released in a helium flash. It would cause the core to heat up and expand. The expansion of the core would absorb nearly all the energy, and, like a helium flash, the explosion might not be detectable from the planet.

Now helium flashes occur in red giant stars, with a degenerate core. That gives more space for thermal expansion without disrupting the core. Things may be different in younger, sun-like stars.

  • Nice straight physics answer - like it. – StephenG Jan 7 at 1:20
  • There is no compelling reason to equate a helium flash to an antimatter-matter explosion. Helium flashes occur when the core is degenerate. In degenerate matter, changes in temperature do not produce a change of volume of the matter. I am not sure this would be the case in a matter-anti-matter annihilation. It is this lack of change of volume of the matter that gives a helium flash its unique characteristics. It also does not consider all of the radiation produced by a matter-antimatter annihilation, and the effects of this radiation.. – Justin Thyme Jan 7 at 2:50
  • ctd Comparing the results of a helium flash to that of matter-antimatter annihilation is like comparing a nuclear weapon explosion to an explosion of TNT of equivalent energy. From Wikipedia 'In the case of normal low mass stars, the vast energy release causes much of the core to come out of degeneracy, allowing it to thermally expand (a processes requiring so much energy, it is roughly equal to the total energy released by the helium flash to begin with), and any left-over energy is absorbed into the star's upper layers. ' That is, coming OUT of the degenerate state takes most of the energy. – Justin Thyme Jan 7 at 3:01
  • It's like melting ice on a lake. It takes an awful lot of energy to melt the ice, before the water below it starts to heat up. ALL the ice has to be melted before the water heats up. But if I put the same energy into an ice-free lake, the water would heat up substantially.. – Justin Thyme Jan 7 at 3:10
  • Its the thermal expansion that requires energy, not leaving degeneracy. However, helium flash occurs in red giant stars, that may make a difference. – James K Jan 7 at 9:43

I am not sure this question is answerable using physics, but it is answerable in magic. The answer is, 'Whatever you want to happen'. In allowing matter and antimatter to coexist, you have gone so far beyond physics as to make physics irrelevant.

We have no idea how antimatter would react to matter if they were not allowed to destroy each other. There is no valid reference in physics as to how the curse could have been implemented. How much energy would it have taken? Where did that energy come from? Because of this wizardry, could matter and antimatter atoms intermingle and intermix freely, or would it require some sort of energy barrier between them?

If this energy barrier collapsed, how much energy would it release?

We know, for instance, that fusion takes a lot of energy to initiate. But once initiated, it releases more energy than it took to initiate. I suspect that, whatever this curse, the removal would initiate some form of nuclear reaction, releasing far more energy than just the matter-antimatter reaction.

Physics tells us that the main radiation from such a process of matter-antimatter annihilation is gamma radiation, with great penetrating power. This would not be a simple 'explosion'. One can not, for instance, compare a nuclear explosion to that of an equivalent amount of TNT.

Antimatter is formed on earth during severe electrical storms. A lot of it. It is neutralized almost as soon as it is formed. But if it were not neutralized? How would it effect our ionosphere? Our magnetosphere? The ozone layer? Communications? It would change what we know about physics, and in reverting back to traditional physics, the implications are just as unknowable as the implications of making the curse in the first place.

To say that everything would be 'business as usual', except that antimatter is not annihilated by matter, simply puts physics aside. There WOULD be many, many other implications.

That last point is the crutch of any answer to the question. By what reason, except assumptions and wizardry, would antimatter atoms remain in the star? What would the theoretical physics be that explains this? How much energy would be required, and in what form?

This is important, because we do not know how much energy would be required to dispel the magic curse. That is, how much energy would it take to reverse the ability of matter and anti-matter to co-exist? Or would removing the curse release even MORE energy? Would removing the curse take up all the energy, so none would be left? Obviously, if matter and antimatter were kept from annihilating each other, it would take tremendous energy to do so.

As an example, would this curse be like bottling up antimatter and constraining it? Therefore, the antimatter in the sun would be equivalent to being in a very strong shell. The energy released by the removal of the curse could all go into destroying this shell. Think a contained explosion where all the energy is used up in destroying the container, vs an unconstrained explosion. The later would have far reaching consequences, the former would not.

Physics can not even answer the question as to what happened to all of the antimatter to begin with. Why didn't the universe just self-destruct at the very beginning? We just don't know enough about the process.

So physics could not answer this question. Therefore, it is entirely up to wizardry. There is no answer except a wizardry answer. This is so surrounded by wizardry, that whatever the author would like to happen, would happen, and whatever the author chose to happen, could be explained by a thick enough physics book.

I would suggest that, if the author wanted a really, really big bang, then the author would posit that all of the energy that went into the curse in the first place, in excess of the energy formed by matter-antimatter annihilation, that is all of the accumulated pent-up energy, was released at the time the curse was removed.

If the author did not want ANY bang, then the author could have all of the energy created by the sudden matter-antimatter annihilation go into reversing all of the cumulative effects of the curse, and cancel each other out. That is, it would be as if the curse had never been implemented in the first place.

Either could be 'supported' by physics.

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