In Alistair Reynold's House of Suns, there is the concept of creating a 'stardam' to prevent unstable stars from destroying nearby systems when they blow up. It says:

A billion or so years later, we began to collect them. We scour space for the occluding signatures of orphaned, starless ringworlds. We fix pushers to their dark sides and launch them across the galaxy at miserable, snail-like fractions of light. It must be done with care, lest the structures shatter into a trillion twinkling fragments. Ringworlds are immensely strong, but they are not indestructible. What they are is shiny. In fact, there is nothing shinier in the known universe. That mirrored inner surface reflects everything, including neutrinos that would happily sail through fifty light-years of solid lead.

To dam a star, to enclose it completely, would require the construction of a Dyson shell. Humans can shroud a star with a swarm of bodies, a Dyson cloud, but we cannot forge a sphere. Instead we approximate one by surrounding a star with thousands of ringworlds, all of similar size but with no two having exactly the same diameter. We make a discus and then start tilting, until each ringworld is encircling the star at a unique angle. The light of the star rams through the narrowing gaps as the ringworlds tighten into their final orientation. Shutters close on a fierce, deadly lantern.

Then suddenly there is no star, just a dark sphere. Inside that shell, the energies of the dying star are held in reflected fury, allowed to bounce back and forth between those flawless reflecting surfaces until, photon by photon, they gradually leak out into space at a harmless intensity.

It takes an unthinkably long time. Should the stardam collapse before most of that pent-up energy has been allowed to dissipate, the results would be more disastrous than the explosion the dam was designed to contain.

My questions are:

  1. The discus would be made of thousands of 'ringworlds' arranged in concentric circles of decreasing diameter (from the outermost part of the discus). If each 'ringworld' is raised by a unique angle on the same side (let's say top-left), all they can cover is the 'top left' and 'bottom-right' part of the potential sphere around the sun. A full half still remains uncovered. Also, can a few thousand 'ringworlds' really cover a supergiant star? An illustration available on the net would be really helpful.

  2. How can a closed sphere prevent the star from exploding? Won't the entire thing burst open as soon as enough pressure builds, like a bomb inside a metal sphere?

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    That seems like a plot armored mirror to me! Commented May 21, 2019 at 13:20
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    The book's physics is internally consistent. It has other objects made of weird matter with unusual properties, so ringworlds with perfect reflectivity and durability are no big stretch.
    – Gaultheria
    Commented May 21, 2019 at 20:27
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    If the width of an individual ringworld subtends 1 degree of arc (at the radius of the ring, obviously) then 180 of them could be staggered about a common "pole" to shield the entire star. Visualize a pair of inter-nested nautilus shells. If they are narrower, you'd just need more of them.
    – DavidW
    Commented May 21, 2019 at 21:22
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    The problem I see is not with blocking all direct light-paths to the star, it's that the rings would have to not be flat relative to the direction of centripetal force. They would need to be perfect circular arcs in cross-section, reflecting all light directly back to the central point, which is not how a ringworld would actually be constructed. (Otherwise a reasonable fraction of the light emitted from the star would reflect from a particular ring onto the back of the next ring inward, and then into space.)
    – DavidW
    Commented May 21, 2019 at 21:24
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    Why not put protective shields around your nearby habitable systems instead, made of the same magical substance as the stardam?
    – Adamant
    Commented May 22, 2019 at 9:21

1 Answer 1


The link provided will take you too an image by the Dutch artist M.C. Escher. It might serve as useful way to picture something like how the star dams are proposed to look. Reynolds talks about individual rings rather than these six armed structures but never-the-less there seems to be some cross over between ideas. If you layer enough of these together you could reasonably expect to occlude an object placed inside them from view. http://www.artnet.com/artists/mc-escher/concentric-rinds-KIACkU7CyZO2C7xYghei2g2

Also here is my own sketch of how the rings might be arranged

As far as the dam exploding due to pressure build up for the plot if I recall correctly (and someone may wish to edit my answer if I am wrong) within the story there is sufficiently advanced technology within this imagined universe to make this technology viable, but failure can happen as mentioned at one point within the story. The quote you provide shows that failure of the dams is considered in universe and implied to happen.

  • 1
    I don't recall them saying how wide a ringworld is, but you'd have to imagine that they're a sizeable fraction of the width of a star if you can occlude a star with a "few thousand".
    – Valorum
    Commented May 22, 2019 at 8:53
  • "but failure can happen as mentioned at one point within the story." That one didn't actually fail, though; it was opened on purpose.
    – endolith
    Commented Jul 17, 2023 at 19:20

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