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A gamma-ray burst can be caused for multiple reasons. Some of the more common ones is that either a supermassive star undergoes a supernova and collapses into a black hole, two neutron stars collide, or a neutron star and a blackhole collide. In most cases, it involves a star. To avoid the first scenario, maybe some civilisations can starlift the star to reduce the mass, prevent the supernova explosion. To avoid the latter, a type 3 civilisation could build a caplan thruster on both stars and push them away. However, both are quite time consuming and might not offer a decent solution if these advents are going to happen sooner rather than later. This is why I am wondering if a blackhole can be used to blow up the stars before they undergo a supernova.

A black hole bomb requires a black hole to be surrounded by mirrors positioned outside of its ergosphere. For a civilization capable of constructing a Dyson sphere, this task could be relatively straightforward due to the smaller scale involved. When an electromagnetic wave is directed at the mirror, a fraction of it will be absorbed by the black hole's event horizon, but a larger portion will be amplified due to the black hole's rotation. This triggers superradiant scattering. If the accumulated energy is not released, the mirrors will eventually fail, resulting in the release of energy comparable to a supernova.

For more information, check this video from Kurzgesagt out.

For a bit of context, putting a blackhole right next to a Neutron star to remove the star's mass will not work, since Neutron stars and blackhole collisions are a source of Gamma ray burst. This is why the blackhole bomb would be used instead, to try to blow up the star before it collides.

To help make things clearer, the blackhole will not be created, nor will it be moved to a star. In the scenario which the question is about, a blackhole and a star are going to collide in each other and cause a gamma ray burst. The closer they get, the faster they orbit each other making slow methods like caplan thrusters useless. This is why they would build a mirror around the blackhole to blow up the star next to it so that there isn’t a gamma ray burst. Just letting the blackhole next to the star be, will not stop the gamma ray burst and also the blackhole is already spinning so all one has to do is to build a mirror around the ergosphere and shot an electromagnetic wave into the sphere of mirror surrounding the blackhole to start the superadiant scatter progress.

Would exploding a blackhole bomb next to a star which is soon going to supernova stop the GRB (Gamma ray burst)? Or would it maybe cause some other bad side effects such as causing the star to explode sooner or stopping the GRB, but being as bad as one... ?

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  • $\begingroup$ Comments have been moved to chat; please do not continue the discussion here. Before posting a comment below this one, please review the purposes of comments. Comments that do not request clarification or suggest improvements usually belong as an answer, on Worldbuilding Meta, or in Worldbuilding Chat. Comments continuing discussion may be removed. $\endgroup$
    – L.Dutch
    Apr 2 at 10:02

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A black hole bomb sounds like overthinking. If you can make a portable, quickly growing black hole that will last without caring, you could just put it near the sun and consume it (if the black hole doesn't collapse immediately), averting a supernova. Expect the outcome for any other bodies in the system to be ugly if you haven't prepared.

Fortunately, your black hole will only need to reduce the star to one similar in mass to ours. After that, it will not go supernova.

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  • $\begingroup$ I think you misunderstood what a blackhole bomb is. It does not suck up the star, but instead it amplifies electromagnetic waves, until they break the mirror surrounding the ergosphere and cause a massive explosion. Having a blackhole right next to a Neutron star will not solve the issue, but instead would cause a GRB. space.com/gamma-ray-origin-black-hole-neutron-star-collision & phys.org/news/2022-07-merger-black-hole-neutron-star.html $\endgroup$ Mar 31 at 13:37
  • $\begingroup$ @TheRocketfan any civilization capable of conjuring up massive black holes will also be able to perform the necessary feats of astrodynamics for their black hole to cause progressive mass stripping of giant stars or even neutron stars without having them collide at any point in the near future, thus rendering them either safe or reducing them to a different kind of explosive fate. Cos they're star gods. $\endgroup$ Apr 2 at 9:58
  • $\begingroup$ @StarfishPrime Since many people were confused about the situation, I edited the question to make it clearer. There is no reason to move an entire blackhole or the stars $\endgroup$ Apr 2 at 18:09
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Aside from the question of the effect it'd have, a "black hole bomb" doesn't create energy out of nowhere, it extracts it from the rotation of the black hole. You would need to first create and spin up the black hole with all the energy you wanted the "bomb" to release.

The capabilities this implies make it hard to believe this civilization doesn't have a better way of preventing the GRB or otherwise dealing with the problem. Even if it's just using the black holes to trigger GRBs with the jets aimed in harmless directions.

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  • $\begingroup$ I think this would be better as a comment than an answer because it doesn’t actually answer the question $\endgroup$ Apr 2 at 4:39
  • $\begingroup$ It's an answer that points out a fundamental flaw in your question. $\endgroup$ Apr 2 at 14:26
  • $\begingroup$ @Christoper James Huff, I have no idea where you got the idea that I said a blackhole gets energy from nowhere. I even mentioned in my answer that the electromagnetic waves get amplified by the rotation of the blackhole. That makes this answer of yours irrelevant. It would be illogical to use a blackhole that isn’t spinning $\endgroup$ Apr 2 at 14:40
  • $\begingroup$ Also saying that there might be a better way that we do not know about does not answer a question that asks if a certain method is possible $\endgroup$ Apr 2 at 14:41
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First of all, mirrors are not guaranteed to reflect gamma rays the same way they reflect light. Few days ago, I stumbled upon this Action Lab Youtube video attempting the same experiment with X-rays, which are still less energetic than Gamma Rays. His conclusion was that X-rays are too energetic to reflect and would penetrate enough to be absorbed. In the case of the mirrors, they were too thin to fit the task. Lesson learned: that type III civilization would construct something of the same size around the gamma rays source, and thick enough to absorb it.

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  • $\begingroup$ I think there is some confusion here. The mirrors reflect electromagnetic waves, which is light. The gamma rays would come from the collision of the Neutron stars or blackholes, but the mirrors around the blackhole just reflect light (aka electromagnetic waves) $\endgroup$ Apr 2 at 19:02
  • $\begingroup$ Yes, I get the point. I'm still curious to know if the bomb you mention picks up enough energy from the black hole's rotation to actually blow a neutron star. Matter emanating from the explosion comes from outside the event horizon, so it must be the matter used to build the sphere. It must hold up enough time for energy buildup and not shatter prematurely. Will the released energy be enough to make an impact? $\endgroup$ Apr 2 at 19:46
  • $\begingroup$ Yes and that is why I asked the question. I don’t know if it can blow up a Neutron star $\endgroup$ Apr 2 at 20:15

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