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I'm trying to create a scenario where the local star is "quickly" (suddenly up to thousands of years) removed, dimmed with reduced output, destroyed (maybe), or otherwise fundamentally changed as to have dramatic ramifications on all life. Keeping the local system in orbit would be ideal, so complete destruction scenarios may not be the best fits.

The biggest challenge I'm having is that the only star-harvesting ideas I know of are variants Dyson concepts, which seem to commonly seek to harvest the energy of a star throughout it's entire/most natural life (implying that this is the most efficient method, which I am guessing makes sense but I don't honestly know). Dyson shells are suboptimal because they can be interrupted by an intelligent outsider leading to the potential to simply "rescue" the star, but more importantly my understanding is that a shell variant would generally be ~1AU in scale for efficiency-sake, making it disruptive to the type of story-telling I'm looking for -- it would either enclose or be obscenely close to most earth-like planets unless I'm mistaken.

Because of this, I'm struggling to think of ways and motivations for an alien or other being to quickly disrupt the local star. I'm looking to avoid scenarios where the star is simply destroyed for the sake of it's destruction, but rather where it is used for a logical purpose by an uncaring 3rd party.

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    $\begingroup$ How much handwavium/unobtainium are you happy with? $\endgroup$ – Starfish Prime Jan 26 at 20:28
  • $\begingroup$ This is interesting - I'm doing something similar, but with a lot of handwavium. (My story has fantasy elements, and a magical creature is growing inside the star and accelerating its fusion process). I'll be interested in the answers to this. $\endgroup$ – Astrid_Redfern Jan 26 at 20:42
  • $\begingroup$ Welcome to the site! Can you specify the technology level these aliens have and how scientific vs magical the solution should be? $\endgroup$ – Zxyrra Jan 26 at 22:30
  • $\begingroup$ @StarfishPrime a fair amount if it doesn't devolve into pure magic, ambiguously defined or unproven ideas should work though. $\endgroup$ – Zolvaring Jan 26 at 22:46
  • $\begingroup$ @Zxyrra Thanks! The aliens in this case should have as much technological capability as is required for the task -- if it's possible to do with a conceptual technology, then for this let's assume they have that technology. I'm trying to avoid defining any magical systems though, unexplainable elements work but only in strictly limited applications, and preferably avoided altogether. $\endgroup$ – Zolvaring Jan 26 at 22:49
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The conceptual technology you are looking for is called "Star Lifting", and it uses the creation of powerful magnetic fields outside of the star to "squeeze" it and force huge masses of plasma to be ejected. At that point the people doing the "star lifting" can capture the plasma, cool it and extract whatever they are looking for from it, and store the rest by condensing it and creating neptune sized artificial planets from the now cold hydrogen and helium from the plasma.

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One method of star lifting. A mechanism for "harvesting" solar wind (RC = ring current, MN = magnetic nozzles, J = plasma jet)

In the pre technological past, observers on Earth might notice visible fluctuations as the sun's output as the system is being installed and calibrated, and eventually would be seeing the new "planets" as they assumed their orbital paths around the sun. Today, it would be unambiguously clear what is happening, but any species which can travel interstellar distances and carry out star lifting is likely not going to be affected by anything that we can do now or in the near future.

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    $\begingroup$ Conceptual... but looking at the Wikipedia page you link to: "Stars have deep gravity wells, so the energy required for such operations is large. For example, lifting solar material from the surface of the Sun to infinity requires 2.1 × 10^11 J/kg. This energy could be supplied by the star itself, collected by a Dyson sphere; using 10% of the Sun's total power output would allow 5.9 × 10^21 kilograms of matter to be lifted per year (0.0000003% of the Sun's total mass), or 8% of the mass of Earth's moon. " Using those figures, after 100,000 years, the Sun would only have lost 3% of its mass. $\endgroup$ – Astrid_Redfern Jan 26 at 22:22
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If "the local star" isn't our Sun, I think I can help you. Actually, I think I can even if it is the Sun, but in the far future.

In "The End of the Sun", two such scenarios are described. These will occur naturally during the star's lifespan, without the need for any third-party intervention, advanced technology or sorcery. You say "thousands of years", so I hope the timescales of 10,000-100,000 years are within the range of what you're looking for.

  • The first of these is the "helium flash", which occurs at the end of the red giant phase for a star that was less than $2M_{\odot}$ in mass during its main sequence phase. It's the point at which the star enters its helium-fusing phase. One such star is our Sun, which is of course $1M_{\odot}$. Over the course of tens of thousands of years, the red giant shrinks to less than 1/50 of its previous radius and luminosity:

By galactic standards, however, the red giant has been shot through the heart. The sudden expansion of the core results in cooling so severe that it is something like the onset of an Ice Age. The cooling immediately leads to much lower pressure in the hydrogen-burning shell that surrounds the core, and therefore to a calamitous drop in the energy output. On a timescale which is almost instantaneous compared to the usual timescale that stars run on (perhaps as little as 10,000 years), the red giant's diameter and luminosity plummet to less than 2% of their former values. For stars the mass of our Sun, the result of the helium flash is a collapse into an orangeish-yellow star with perhaps ten times the current solar diameter and 40 times the luminosity. It is quite a comedown.

  • The second scenario occurs roughly one hundred million years later, as the Sun (which has become a red giant again) reaches the end of its helium-fusing phase. During this time, it's been burning both helium and hydrogen. The explanation is rather complicated, but:

In four or five huge bursts, spaced roughly 100,000 years apart, the outer layers of the Sun will separate from the core and be completely blown away. They will form an enormous, expanding shell around the solar system, and move outward to rejoin the interstellar gas. Roughly 45% of the Sun's mass will escape in this way. The remaining 55% of the Sun's mass is soon compressed into the white-hot, ultra-dense core.

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  • $\begingroup$ In your text you say the sun shrinks and darkens but the quotation has strange wording of 'collapse .. 10 times current diameter'? Is there some big expansion first? $\endgroup$ – quarague Jan 27 at 10:13
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    $\begingroup$ @quarague it is what happens after transition to red giant status, which can have diameters of over 100x that of the sun. $\endgroup$ – Starfish Prime Jan 27 at 14:17
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See Stephen Baxter’s Xeelee series for an example of this in fiction. Dark matter life-forms called photino birds live in the gravity wells of normal baryonic matter stars, but novae and supernovae disrupt their habitats, so they use their technology to stop nuclear fusion in stars and prematurely turn them into white dwarfs. (In real life, there seems to be strong evidence that dark matter doesn’t interact with other dark matter, and so couldn’t give rise to life.)

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The Photino Birds from the Xeelee sequence. Creatures made of dark matter that feed by orbiting through stable gravity fields. They're uneffected by heat or essentially any other normal physical processes.

Because they like stable gravity wells, white dwarfs are their ideal environment. They REALLY don't like black holes or neutron stars. They "infect" a star and moderate its fusion process by playing with its gravitational field, turning it into a dark, dead ball of gas that they can feed on for eternity.

They have almost limitless control over gravity, making them formidable foes. The only way to kill one is likely with a near luminal speed microscopic black hole or some other incredibly intense gravitational field, tearing them apart.

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  • $\begingroup$ That's one of the most fasinating science fiction ideas I've ever heard. I need to check out these "Xeelee" books. Actually, maybe you might want to edit your answer to mention that Stephen Baxter was the author? $\endgroup$ – Astrid_Redfern Jan 30 at 21:43
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I'm trying to keep handwavium at a minimum... The aliens need hidrogen and helium in super large scale. So they stop by the closest star in their path and steal massive amounts of gases from it, using magnetic fields or a tracktor beam. Once the containers are full, they set again on their merry way.

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    $\begingroup$ How would magnetic fields allow them to harvest gases? Hydrogen and helium aren't magnetic. $\endgroup$ – F1Krazy Jan 27 at 15:00
  • $\begingroup$ @F1Krazy ...but most of the hydrogen and helium in a star is ionised, and magnetic fields can affect plasma. That's the meat of Thucydides' answer, which is slightly better elaborated. $\endgroup$ – Starfish Prime Jan 29 at 7:59
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A Dyson shell doesn't have to be at 1AU, only if you want to have a similar insolation on the shell's inside as we have here on Earth. A closer shell will harvest the sun's energy more efficiently, and you can actually have a series of shells which each feed of the residual radiation given off of the inner ones.

Star lifting is a (slow) method of deconstructing a star, but it can actually also be used to extend a star's lifetime, by mixing up its interior, to prolong hydrogen fusion in the core. If the aliens are defeated, their captured star lifting gear could be used to repair the damage done.

A more final, and probably quicker, but also more speculative, method would be a Strangelet Bomb. A Strangelet is an exotic particle that (hypothetically) would "infect" normal matter and grow without bounds on contact. If you shoot such a thing into the sun, it would be converted into a strangelet itself, with unknown, but probably dire, consequences.

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  • $\begingroup$ I don't think the consequences are that unknown: the Sun would end up being a lot smaller and a lot cooler, and during the process it would emit quite a lot of radiation (gamma rays seem to be the usual case here). It doesn't quite answer the "why" though. It'd work, if strangelets were suitably stable, but a huge blob of strangelets seems like it would be less useful than a star, no? $\endgroup$ – Starfish Prime Jan 29 at 8:01
  • $\begingroup$ Who said anything about useful? "a logical purpose by an uncaring 3rd party" could be a science experiment - "what happens when you throw a stragelet at a star?" $\endgroup$ – ths Jan 29 at 9:30
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The Dyson fleet...

They are nomadic constructors that move through the universe like locusts, eclipsing stars. They come to the Sol system with a small Dyson sphere in parts, to harvest the light in the shape of electric energy as step one. They start by mining away Mercury and Venus while a seemingly endless convoy of ships that hold and are the panels and struts they had used in their previous victim's system. And they build between the Sun and Earth. The first result is simple: Sol gets eclipsed more and more as construction goes on, which puts Earth into total darkness for longer periods, and as soon as construction is far enough, eternal darkness. They build it at 0.5 AU, because that saves a LOT of material. What do they use all the energy for?

...to harvest the plasma...

They use the power of the star to power a plasma accelerator on the outside of the sphere to generate the fields needed to harvest what they actually want: the plasma.

Shooting particle streams shallowly into the sun, they manage to rip a constant stream of plasma out of the surface, pulling this stream of ionized hydrogen into the accelerator and refuel their locust convoy. The same convoy that is pretty much a Dyson sphere in parts.

...and move again

Once their ships tanks are full, the Dyson sphere once again sets sail, piece by piece re-illuminating the solar system after several long years without a single spec of light to the Sol system. The sun is diminished from yellow to a red dwarf, faint in the sky. Its lifetime might be cut in half, its luminosity surely is cut down.

Earth's lot

The result is, that during the first "dark week" the planet plummets into a short Ice Age, the climate recovering once the planet is back in the light. Then the real Ice Age starts, as the planet is in the dark for months, only getting a short warm phase before it turns into an ever frozen ball of ice once it is in eternal darkness.

Then, the eclipse ends. It might have been a couple long years or decades, but then the weakened sun stands back in the sky. But it is not enough to melt the ice on the planet Earth...

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