Assuming in a galaxy far far away there is a Type 2 civilization (currently on the verge of making the transition to Type 3).

Their scientists predicted that the star (red giant) they are orbiting is going supernova probably within a couple of years (a decade maximum), they won't be able to evacuate everybody in time.

My question is how can they stop the supernova? If it can't be put out in time how can they survive this ordeal?

Note: I'll accept any good answer such as the scientists somehow managed to build a king size Noah ark that can sing opera finds and fits itself inside a cosmic superstring located just outside their planetary system (call it coincidence) and come out at the other side of the universe unharmed but visibly shaken.

  • $\begingroup$ From your closing remark, I take it that it's not categorized as science-based. But is it magic / fantasy? Or what exactly is not sciencey but not a fantasy genre? $\endgroup$
    – JDługosz
    Commented May 7, 2015 at 7:14
  • $\begingroup$ @JDługosz thanks for pointing this out as you see a cosmic string has been proposed by physicist long ago however it is still elusive so long there is no experiments to disprove such claims I'll just fall for it with no string attached. $\endgroup$
    – user6760
    Commented May 7, 2015 at 7:19
  • 23
    $\begingroup$ Want to leave this quote here: "Which of the following would be brighter, in terms of the amount of energy delivered to your retina: 1. A supernova seen from as far away as the Sun is from the Earth or 2. the detonation of a hydrogen bomb pressed against your eyeball? The supernova -- by nine orders of magnitude." -- XKCD what-if #73 $\endgroup$ Commented May 7, 2015 at 10:02
  • 4
    $\begingroup$ Drop some red matter $\endgroup$ Commented May 7, 2015 at 14:22
  • 1
    $\begingroup$ The only way to survive a supernova is to not be there when it goes nova. Even if it goes hypernova with a black hole forming and all, you still get a lot of very hot matter and very high energy radiation blasted outwards when the light outer layers are inevitably sluffed off. In a true supernova, any planets in the system don't survive. So your only option is to get yourself gone. $\endgroup$
    – Jim
    Commented May 7, 2015 at 17:43

7 Answers 7


A Kardeshev Type II civilization capable of transitioning to a Kardeshev Type III should no longer be bound to a particular planet or even a single solar system. They should already be able to move populations from world to world with little effort having already mastered the ability to harness energy from thousands or even millions of stars in their civilization.

BUT for the sake of argument, let's say you have a highly advanced type II civilization which has mastered energy for an entire solar system by harnessing the power of their star and now they discover their star is unstable.

  • With their level of science, they would be able to determine how long their sun was going to survive. They would have mastered technologies which related to the rate of output, the age of their star, their star's expected lifespan and rate of fusion decay.

  • All things considered, most stars ARE fairly stable and relatively long lived. And a star which has lived long enough to have a civilization form around it (if this is the species host star) is liable to be a second generation star and very stable overall.

So let's add to the challenge and say, it is a large second-generation star whose mass is high enough to become a supernova. Since you specified red, it would have to be a very large red giant, like the star Betelgeuse. A massive supergiant whose fuel source was running out could conceivably go critical and become a supernova. The process of becoming a supernova is incredibly slow, on the order of ten million to ten billion years.

With these suppositions in place: Could anything stop it from doing so?

  • Possibly, it would depend on the level of technology available to the species in question, how fast their star was burning its fuel source and how close to nova their star is.

First things first:

  • In most cases, you don't extinguish supernovas. You prevent them. The energy output by a supernova is so great that once a star explodes, there is almost nothing to be done except to be very far away and enjoy the show. Once a star has gone supernova, there is no stopping the action because the overall process is slow to build but once its going, it won't stop.

This is a simplified representation. A star is composed of two primary forces, expansion due to the fusion reaction and compression due to the force of gravity:

  1. Conversion of hydrogen atoms into helium atoms. It will do this until there are no hydrogen atoms left to convert. This conversion creates an expansive pressure pushing matter away from the center of the star.

  2. Gravity compresses matter causing its collapse toward the gravitational center of the star.

    • These two forces, gravity crushing down and the explosion of energy coming up balance each other and create the energy output we know as a star. As a star consumes its store of hydrogen it will, if it's massive enough continue to try and convert the helium into heavier elements until it can no longer sustain nuclear fusion to do so.

    • If it reaches the element of iron, it will simply no longer sustain fusion, period. Most stars will top out at carbon because the energy required and the mass needed to keep fusing are a delicate balance. When a star maxes out at carbon it basically becomes a hunk of cooling material and will die as a small dwarf star.

enter image description here

  • However, there is another extreme. When a star is massive enough to burn through its energy supply, it may do something else. When the energy pressure from the star is no longer great enough to keep the mass of the star from crushing down, it may simply collapse violently and then explode in a burst of energy called a supernova.

  • The supernova uses up all of the remaining fuel in an orgy of energy output dwarfing anything the star has produced all of its life, in single second. If a star becomes a supernova, it may fuse elements all across the periodic table and this is where the heaviest elements in the universe can be found, the byproduct of first generation stars who exploded violently to create the building blocks for second generation stars.

So if you wanted to prevent a star from exploding violently and you were a species capable of spaceflight but you need centuries to evacuate your star system, you might:

Number One:

  • Find a new fuel source for your star. A new source of hydrogen or helium would slow the degradation rate of your star giving you more time before it completely collapsed.

  • If your star system had two or more gas giants, if your species could move entire worlds, they might want to place the gas giants in orbits closer to the sun and allow the sun to draw mass from the giants adding to its fuel supply. These would have to be massive worlds, nearly stars themselves (See: Brown dwarf) to offer any reasonable amount of mass capable of delaying a star's collapse.

enter image description here

  • The other alternative would be to bring mass from another nearby stellar body and do something similar. The energy required to move a planet would be dwarfed by the effort required to move a star, even a very small one, so this is the far harder of the two tasks. A star, however, would be more favorable since it has more potential fuel to work with.

Number 2

  • Slow the rate of stellar reaction within your star. If you could slow your star's rate of fuel consumption, (See: Stellar Husbandry) this could conceivably buy more time, since it is the fusion of mass which causes the star to use up its fuel. However, reducing the reaction rate could also cause the star to collapse as the energy of the star's output keeps mass from being forced closer to the star's surface which ultimately could cause the same nova you were trying to prevent.

enter image description here

  • Somehow you would have to buffer the reaction but keep the star "fluffy", perhaps by using artificial gravity to simulate the pushing motion of a star's energy output and keeping the mass from collapsing into the body of the star prematurely triggering the supernova.

Why would any species do this, even assuming they were able to do either?

  • Both of these ideas posit incredible capacities, which might be available to a transitioning type II to type III civilization but both seem fantastic in terms of their energy requirements.

  • I did have a reason to consider both of them, though. If your species is limited to slower-than-light or relativistic travel, even if they had ships capable of evacuating their worlds, they would need to delay the supernova for as long as possible in order to reach a "minimal safe distance" (likely some number of light years, at least).

  • This means the long-term benefit would be worth the effort if it meant you had another 1,000 to 250,000 years to get as far away as possible.

Other References: How Supernovas Work

  • 3
    $\begingroup$ Trying to add fuel to a normal-size star is likely not as easy as your might expect as only small stars (mass < 0.3 Sol) actually have fully convective mixing between the core and and outer layer. If you started much earlier, the mixing process might be enough to help, although you then get into the problem, adding more fuels only makes them burn faster. Never tried the math to see which effect would dominate. $\endgroup$ Commented May 7, 2015 at 7:24
  • 1
    $\begingroup$ For me, this was purely a theoretical exercise. I didn't crunch any numbers but I do know adding fuel could, if done improperly, only exacerbate the problem. And if you possess the capability to do the math, I bow to your superior knowledge and capacity. $\endgroup$ Commented May 7, 2015 at 7:28
  • 8
    $\begingroup$ The math is actually easy, if you make enough simplifying assumptions. If you add mass early in the solar main sequence, you always lose. If you add mass late, you win, but you have to start early enough to give the new fuel time to mix into the core, so it gets complicated. WIth only a decade left, it is a complete waste of time even trying unless you could inject fuel directly into the core. Nice answer overall. $\endgroup$ Commented May 7, 2015 at 7:40
  • 1
    $\begingroup$ Adding fuel won't help. The problem is the iron core is approaching critical mass. $\endgroup$
    – Joshua
    Commented May 7, 2015 at 16:44
  • 6
    $\begingroup$ Adding fuel isn't going to help - a star large enough to explode as a supernova is orders of magnitude larger than its core's convective zone (the region of the star in which the fuel for fusion circulates). Hydrogen outside the core's convective zone will never fuse. Only in the smallest stars (red dwarfs, and maybe not even all red dwarfs) does the convective zone encompass the entire star. Adding hydrogen to a massive star is only going to increase the mass of the star (and therefor its fusion rate) without actually increasing the amount of hydrogen available for fusion. $\endgroup$
    – asgallant
    Commented Jul 19, 2016 at 6:57

A star does not go supernova "within a couple of years". A red giant is the beginning of the decline, and that will cause disruption already: ours will swallow the Earth (or possibly leave a scorched iron core remnant), for example.

The star will cycle for millions of years as it moves up to higher elements and temperatures.

The end is indeed sudden, but you're already far away from the original home orbit and a dyson sphere kind of thing is even less practical than normal because of the enormous size of the red giant and the high solar wind.

So, even if you suddenly find that the projections are off by far enough that your final evacuation is not ready, you will already be living out around Neptune. But... a star like ours will burn out and not become a supernova. So you're talking about a star with at least 8 solar masses. The red giant will be even more huge, so your living places will be very far back.

You might not evacuate the solar system on short notice, but can find shelter nearby. Like, get behind a Neptune-like planet, such as the one your habitat is orbiting already.

Now the bad news: the blast of electromagnetic radiation is easily blocked by a planet or constructed shield. The problem will come from neutrinos. The flux is so incredibly high that it will transmute a significant number of atoms in your body and every other material, and the planet-sized shield won't stop it.

A T2 civilization will be beyond our comprehension, not just 1950 but in space. They may not use biological bodies. They will have advanced nanotechnology. Maybe they will turn themselves into spores that are designed to weather the conditions by using redundancy and storage systems that physically won't mind a little transmutation. Maybe they will beam themselves elsewhere. Maybe they will become one with the star and live on as energy beings. Maybe they will all be destroyed and restored from backups made before they went to study the star close-up, and will be sorry they lost the continuity and richness of memory (but not all memory since updates are sent out periodically).

See here for more about supernovae. You should read up on that as a prerequisite, not just learn a little from what questions you thought to ask.


They go back in time to when their sun was young and hydrogen rich and encase the entire star in a oversize General Products Hull that neatly encases their sun. Or perhaps, they are just good planners and don't need to travel back in time.

Due to the GP hull, the sun lasts longer than it otherwise would since it is not wasting its hydrogen on solar flares and solar wind. In the late stages, the additional pressure on the star keeps the star from even going into the giant/supergiant phase as the helium burning phase kicks in. During the main sequence phase, the fuel losses are actually quite minor, but they become quite large in the later stages of a star.

If the stellar radiation becomes too intense over time, your can even activate the Slaver stasis shield, cycling on and off the sun rapidly (hundreds of time per second you would not even notice), adjusting the duty cycle to match the desired level of radiation. This would also obviously extend the stars life.

This should extend the useful life of their sun by many millions, if not billions of year. If the alien race is emotionally similar to the Puppeteers, they would perhaps prefer this method over evacuation anyway. It is similar to the Puppeteers solution to their problem in that respect.

I've read the Fleet of Worlds and know how the Puppeteers build a hull, so this is not completely practical at that level, but perhaps an alternate hull construction technique would be possible, or just another similar technology.

Sadly, the real answer to the question as postulated is that it cannot be done. 10 years is not enough time to make any difference sans time travel. Even if you have fully advanced Von-Neuman machines at your service, you can't make a change to the core of your sun in ten years. No non-magical machine can penetrate to to core of a star and alter its composition because of the temperature are hot enough to turn all matter into plasma quickly.

To prevent a nova, you must change the core. And if you have magic tech, surely you could evacuate to safety,

It occurred to me later that our aliens actually could penetrate the core. All you have to to is target your sun with a gas planet traveling at very high velocities. A small red-giant is about 20 solar diameters, so lets assume a radius of 12 million km. The radius of 12 million km can be traversed at .1 c in about 400 seconds. Since the photosphere is not very dense, the gas planet could hit the core largely intact. Note, that .1 c may simply be faster than needed -- .01c means 4000 seconds (1.1 hours) to reach the core, don't know the lowest speed that would allow you to hit the core which depends on the size and the planet and what percentage needs to penetrate the core.

I am pretty sure that this would be a bad day for our aliens though as the impact would cause huge solar solar flares, and the sudden influx of new hydrogen fuel would perhaps react at a greatly accelerated pace since the core temps are much hotter than those needed to fuse hydrogen.

But, instead of dropping in a planet, why not drop in a big lump of frozen hydrogen enough for say 1 minute worth of fusion, 42 billion metric tons of hydrogen. Now the splash "crater" and solar flares are much smaller and I am pretty sure that most of the hydrogen can still penetrate to the core. Optimize the size and speed of your hydrogen ice balls and repeat as needed.

Even given this strategy, I still don't think it actually helps out the aliens. The core will become even hotter as most of the new fuel burns much faster than the current helium/carbon, etc. core. So the existing core will simply burn faster. I think you have to remove the heavy atoms in the core at the same time you refuel it to actually drop the core temperature. We hit the magic tech required level once again.

So, still no happy answer. But maybe this gives someone an idea for saving the day.


Here's an out-there idea that might make a good plot.

They are there studying the red giant and eventual core collapse close up. Maybe they plan to use the energy of the supernova to do something, and is part of their development plan for moving to type-III. Perhaps it is to generate a wormhole or warp drive experiment or study physics at very high energy beyond existing experiments. So, maybe they have tinkered with the stellar core and accidentally accelerated the collapse!

Maybe the energy_harvesting thing will prevent a normal supernova as the energy is taken for some use. Their plan is to quickly modify the apparatus to take almost all the energy, even though that wrecks the experiment or engineering effort involved.

Maybe they are creating a wormhole and they can manage to, use it to escape by swallowing the entire habitat, before the blast reaches there (light-hours away). Or not a wormhole but space-warping stuff, so they shape it to form a fork on front of them and remain protected in the lee, or make a bubble around them, or something.


Wikipedia's article on the Kardeshev Scale predicts that a Type II civilisation may have access to star-lifting processes.

It seems highly unlikely that if a T2 civilisation were unable to evacuate a solar-system within a certain window, they'd be able to prevent a giant nuclear explosion in less time.

The most plausible option seems to be;

Attempt to delay your solar-apocalypse as long as possible while you evacuate as many as you can.


Looking at the answer Thaddeus wrote it occurs to me that since you are talking about the balance of energy production and mass, it would be optimal to directly add energy to the star without adding mass even if you expect that mass to work as fuel. This has some benefits:

No added mass. If you add mass it increases the size of the star and even if you manage to make it postpone the super nova, it will still happen and probably become more energetic. Although with super novas that is not really relevant.

Propagation. While energy, just like mass, will be added to the surface not to the core, energy will reach the core with conduction and radiation (actually reduced conduction and radiation of energy away from the core) even if convection is too low for new fuel to reach the core. You make the surface hotter, the core will lose heat lower and collapse will be postponed.

Evaporation. Increasing the surface temperature will make the star lose mass faster thru stellar wind. Reasonably this would not be significant, but it might be possible to make some specific spots on the surface very hot with lasers or similar focussed energy. This might allow stripping mass off the surface in a controlled fashion. It might be possible to trigger fusion reactions on the surface, which would make feeding energy to the star much easier. And the explosions might be capable of stripling noticeable amounts of mass.

Civilization level. The level of civilization specified in the question is pretty much defined by the fact that it has access to sufficient energy for this. They should be capable of building mirrors or other infrastructure capable of using a significant portion of the stars energy output to make it cool slower. And have enough control of the process to keep any habitable planets habitable.

  • $\begingroup$ OK, suppose we add lots of energy to the star that migrates to the core. The plasma in the core will be hotter and fusion reactions will be more common. So your star novas sooner, not later. $\endgroup$ Commented May 8, 2015 at 7:07
  • $\begingroup$ @GaryWalker The premise is that the rate of fusion at the core was already falling. In any case, heating the surface can't really make the core hotter, it is too hot, just slow down the cooling. Should edit to make that clear, probably? $\endgroup$ Commented May 8, 2015 at 8:12

Build a Dyson sphere around the star, with an opening pointing away from your system. You might be able to deflect much of the matter way from your system, but the supernova will happen nonetheless.

  • $\begingroup$ I'm having trouble visualizing how that would help. If anything, it seems like it could make matters worse. Could you please elaborate on your reasoning? $\endgroup$
    – user
    Commented Sep 12, 2016 at 21:12

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .