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Death of stars are fun and make for a great premise, but the actual dying of stars that are conducive to intelligent life aren't so interesting. Stars that can go supernova are too short-lived to harbour intelligent life.

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How do you kill a star such that a civillisation is around to witness the horror of this happening and attempt to avert or escape the catastrophe?

It'll be great to have answers that consider different time-frames, 10,000 years, 100,000 years. 1 million years might be pushing it for how relatable the story can be.

Background

I'd like a set up where the civillisation not only has to try and escape the death of their sun, but also an impending supernova. It would be better if these two events are directly connected.

I also wouldn't mind some science fictional answers (The 'currents of space' was mentioned in another dying sun question, which I thought was quite an interesting way to kill a sun, although it's now dated).

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    $\begingroup$ Must it be the host star? A nearby star going supernova is also going to ruin a civilization's day. $\endgroup$ – Erik May 26 '15 at 8:20
  • $\begingroup$ @Erik No, it doesn't have to be limited to the host star... I'd say that's actually one possible answer... $\endgroup$ – Isabella Chen May 26 '15 at 9:12
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Another possibility for a supernova--stellar collisions. Start with a multi-star system, several that are in close but stable (resonance) orbits, the one with life is in a more distant orbit. The resonance kept things good for the billions of years needed for life to evolve but as they age they have gotten brighter and developed a much more powerful wind--and now their close orbits are spiraling in due to drag. Once two hit the drag issue gets much worse, the rest fall in pretty soon. Now we have a several billion year old star that's big enough to supernova.

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It doesn't neccesarily have to be the host star that goes supernova. While stars that can go supernova might not live long enough, it's possible for an older star with life around it to exist in proximity to a younger, more volatile star.

A lot of things can happen as stars move around and you might get unlucky and have a critical star move close to your system as galaxies rotate. Or it could have been there all the time. At a few dozen light-years away, a star going supernova will still be a catastrophic event for your civilization.

XKCD helpfully explains just how big a supernova is by explaining that something a sun's distance away going supernova delivers more light to your retina then detonating a nuclear device pressed against your eyeballs. (by 9 orders of magnitude)

According to this wikipedia item on Near-Earth Supernova, a supernova can have a noticable effect on the earth's biosphere if it occurs up to 100 lightyears away. There's over 10.000 stars within that distance from the Sun. Plenty of accidents just waiting to happen, no need to kill anything.

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  • $\begingroup$ What would we do without XKCD? Given how often the site gets referenced, I wonder if the author's here somewhere... $\endgroup$ – Frostfyre May 26 '15 at 13:05
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Part of this depends if you are dealing with a type 1 or a type 2 supernova, as the mechanisms are different.

A type 1 supernova occurs as a neutron star sucks hydrogen from a companion star, building up a layer of hydrogen on the surface. Because of the massive gravitational gradient, the Hydrogen is being compressed to near nuclear density, and as more hydrogen infalls from the companion star, the pressure on the static column rises until the conditions to initiate fusion exist. All the hydrogen stuck to the surface of the neutron star fuses all at once (or close enough to that) and an incredible display of light and energy occurs.

Since this is reasonably well known, the civilization needs to observe the neutron star closely and calculate just how much hydrogen has already fallen to the surface of the neutron star in order to calculate how much time they have to prepare. With enough superscience, they could find a way to interrupt the infall of hydrogen from the companion star, averting the Type 1 supernova.

A type 2 supernova is much more powerful, and harder to interrupt. As a giant star star burns its hydrogen, the helium "ash" accumulates in the core. When the hydrogen runs out, the gravitational pressure takes over and the core starts to collapse, until the pressure is great enough to initiate helium fusion. The cycle continues at shorter and shorter intervals as elements higher up the curve of binding energy are fused (oxygen, carbon, silicon and so on). Once you reach iron, the cycle ends, since there is no net energy from fusing (or fissioning) iron. The gravitational potential takes over and the mass of the star falls inwards for a core implosion, leading to the massive release of energy that is a type 2 supernova (and the extra energy needed to create the heavy elements beyond iron in the periodic table). A type 2 supernova can outshine the entire galaxy for a short time, hence the need to not be in the neighbourhood when that happens.

A huge handwave to stopping a supergiant star from collapsing into a type 2 supernova would be to somehow strip mine the upper layers of the star and eliminate the mass which will drive the collapse of the core before the star fuses all the nuclear fuel into iron. Your civilization will need ultrascience to accomplish that sort of stellar engineering...

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I suppose that's something that is recently known: how do clusters of new stars dispurse and mix with other traffic in the galaxy. How long before an "open" cluster clutch loses stars that might then approach old stars in the galactic orbit?

How old can a star that dies in such a fashon get, in the smallest (slowest) such stars? Maybe there's plenty of mixing time.

Anyway, my assumption is that a suitable star approaches within dangerous distance of the protagonist's sun. They would have a nearby red giant in their entire development history. What would that be like in the night sky?

In Dragon's Egg, Robert L Forward described how the intellegent species (living one million times faster than us) incorporates the visiting (conspicuous) spacecraft and apparatus into their culture. The ship proper was The Eye of Bright, first a god, still culturally important and the name of the university where the eventual contactees work.

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Your question actually asks (I think) two questions:

  1. How do I get an intelligent civilization in proximity with the type of star that goes supernova
  2. Once I've achieved that, how might an intelligent civilization prevent or delay that supernova.

1. Getting it near a civilization
Generally speaking stars capable of supernova form, burn, and explode long before life could get really established. Also the locations conducive to forming these stars isn't the same sort of location that create smaller stars (like our Sun).

However, there is something called Runaway Stars. These are stars moving at very high velocity (relative to other stars in their neighborhood). One type of these stars is formed when one of a pair of high mass stars explodes in a supernova and the smaller star flies into space at high velocity.

One example of a related set of runaway stars is the case of AE Aurigae, 53 Arietis and Mu Columbae, all of which are moving away from each other at velocities of over 100 km/s (for comparison, the Sun moves through the galaxy at about 20 km/s faster than the local average). Tracing their motions back, their paths intersect near to the Orion Nebula about 2 million years ago. Barnard's Loop is believed to be the remnant of the supernova that launched the other stars.

Such a mechanism might explain the proximity of a supernova star near inhabited systems.

2. Stopping the explosion
For the answer to #2, please read @Thucydides fine answer. Essentially, you can't stop a Type 2 supernova. However, you might be able to delay the explosion by feeding it extra hydrogen fuel as it passes your system and gets to a safe distance. Just remember that you'll literally be "playing with fire". Any small mistakes and KABOOM. Also there's essentially no mixing between upper layers of these stars and the layers which perform fusion, so this solution requires much super science to make plausible.

You might be able to stop a Type 1 supernova but stopping it from feeding off another star.

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  • $\begingroup$ Playing with fire indeed! First of all the Sun fuses 6.2 * 10^8 kg/sec of hydrogen, so you would have to inject at least that much into the core of the pending supernova. Since the conditions of the core are more extreme as heavier elements are fused, the Hydrogen would be very disruptive, either interrupting the reaction or fusing far faster than normal. The disruption of the core would probably trigger the supernova as gravity takes over, rather the opposite to what you want. $\endgroup$ – Thucydides May 28 '15 at 2:41
  • $\begingroup$ See this question $\endgroup$ – JDługosz Apr 26 '16 at 13:41
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A star doesn't have to go nova or supernova in order to "die" from the perspective of the civilization depending on it. Our sun, when it runs out of unfused hydrogen and reaches the end of its primary cycle, will expand into a red giant. That expansion will envelop the earth and destroy all life on the planet.

We don't currently know enough about the lifecycle of stars to say exactly when this will happen, although it is thought to be millions if not billions of years off. We know the major stages that differently-massed stars go through, but we don't really know what it looks like up close shortly before they enter a new stage.

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