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Asking for a fictional storyline.

Say a type iii civilisation on kardashev scale want to make a star go supernova. Then what are the possible ways to achieve this?

The said star being massive enough to go supernova on its own in a few million years.

Would collapsing a Dyson sphere made of iron into the star do it?

What would be the relation between weight of iron and stars mass that would kill it?

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  • $\begingroup$ I don't think this is the place for your particulat question, but I just want to point out, if you are thinking about Dyson Spheres, that Dyson himself knew they would be a collection of nodes, connected by articulated sections. A complete sphere is "engineeringly" impossible to build $\endgroup$
    – user171879
    Commented Oct 30, 2017 at 19:33
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    $\begingroup$ Really this should be asked on Worldbuilding SE. What a type 3 Kardashev civilization could do is way beyond speculation. $\endgroup$
    – StephenG - Help Ukraine
    Commented Oct 30, 2017 at 19:42
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    $\begingroup$ @StephenG Have Tried Asking Such Questions There But Guess What They Say They Are a fictional content websites so matters relating to real world physics so go to physics SE. lol $\endgroup$
    – user1062760
    Commented Oct 30, 2017 at 19:45
  • $\begingroup$ @User171879 yeah I'm not calling for a sphere like a ball but say a giant honeycomb structure not entirely continuous. Like an iron grid $\endgroup$
    – user1062760
    Commented Oct 30, 2017 at 19:49
  • $\begingroup$ Fair enough, it was the symmetry of the infalling complete sphere that I thought you might be considering for a realistic plotline. $\endgroup$
    – user171879
    Commented Oct 30, 2017 at 19:55

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One obvious way of making stars go supernova is to drop a black hole inside it. Unfortunately, the accretion rate is surprisingly slow for small black holes. Assuming Bondi accretion, $M'\approx \pi\rho G^2M^2/c_s^3$ where $c_s$ is the local speed of sound. If we assume $c_s\approx 0.1c$ and $\rho\approx 10^{12}$ kg per cubic meter I get $M'(1M_\odot)\approx 1M_\odot$ per second (instant boom), but for a Jupiter mass hole $M'(1M_J)\approx 10^{-6}M_\odot$ per second (about 11 days) and for an Earth mass hole hole about 3,400 years. Same thing for dropping a neutron star or lump of strangelets inside.

This may take a while, especially since there is also an upper limit on the accretion rate due to the Eddington luminosity where the radiation from accretion produces a light pressure that counters the gravity. This limit is around $\dot{M}_{Edd}=4\pi GM/\epsilon c \kappa$ where $0<\epsilon<1$ is the efficiency of converting rest mass into energy ($\approx 0.1$ is standard), and $\kappa$ the opacity ($\approx 3\cdot 10^{-15}$ m$^2$/kg). For a Jupiter mass black hole this is about $8\cdot 10^{-6} M_\odot$ per second so the flow does not choke, but for a solar mass hole this is $9\cdot 10^{-3} M_\odot$ per second - the inflow chokes (this is avoided in "proper" gravitational collapses).

While iron seeding sounds good, you need to add astrophysically significant amounts of iron. I suspect this would be on the order of solar masses, also troublesome.

My best bet would be if one could set up radial oscillations to induce a proper gravitational collapse since the star is by assumption close to the end anyway - maybe a bit of a push is enough. Helioseismology is not my forte, but I can imagine some stars could be pushed over (this at least may happen in white dwarf Type Ia supernovas). You would "just" need to drive the oscillation somehow, perhaps by coupling other modes using your K3 tech.

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  • $\begingroup$ Nice answer. I imagine the iron inside a star, once the fusion stops would undergo the equivalent of chandrasekhar collapse, so you probably wouldn't need solar "Masses" of it, a bit over 1 solar mass should be close to enough but it would need a good bit of time to coalesce in the center and condense. How about adding a Neutron star? $\endgroup$
    – userLTK
    Commented Nov 1, 2017 at 8:40
  • $\begingroup$ What does "the inflow chokes" mean? $\endgroup$
    – blademan9999
    Commented Jul 12, 2023 at 15:39
  • $\begingroup$ @blademan9999 - The inflow meets the massive radiation pressure from inside, slowing down or even nearly stopping. $\endgroup$
    – Anders Sandberg
    Commented Jul 16, 2023 at 8:54

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