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So in my concept, humanity needs to permanently destroy an enemy planet. But their defense systems won’t allow the humans to get close enough to destroy the planet with whatever weaponry. Would it be possible to somehow start a black hole or singularity in the system to destroy the planet?

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    $\begingroup$ How far is this planet away? Far enough for a blackhole not to bother the home planet? How is this generated black hole able to reach it but not something like a miniature star sent their way? Is this something that could then be used to destroy the home planet, or a defense to protect against is? How much energy do they have to work with? $\endgroup$ Commented Mar 16, 2022 at 0:30
  • $\begingroup$ It’s a long while away, it would be close to the human border though. I was thinking that the enemy was using humans and turning them into cyborg killing machines. Idk if what I’m saying is realistic or not, my idea of what distance is in space is basically just stellaris maps. @DangerLake $\endgroup$ Commented Mar 16, 2022 at 0:35
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    $\begingroup$ We need some more information to be able to answer this, especially regarding the technology that the humans have available, the type of star that the enemy planet is orbiting and other bodies in the enemy system. (Making a black hole requires truly vast amounts of mass, much easier to use what is already there than try importing planetary/stellar masses.) $\endgroup$ Commented Mar 16, 2022 at 1:46
  • $\begingroup$ @KerrAvon2055 yeah you’re right, this is my first post I didn’t know what to include. In this scenario humanity is at least 1000-2000 years advanced from now. The planet orbits a g-type star (like ours) and is a similar distance from the sun as mars. 2 moons. There are various other planets in the system as well as an asteroid belt. (Pretty similar to ours) $\endgroup$ Commented Mar 16, 2022 at 15:41
  • $\begingroup$ If the black hole is intended to destroy the planet, then it’s weaponry. But your conditions state that the defence systems won’t let the humans get close enough to destroy the planet with whatever weaponry. So there’s a contradiction in the question. Other long-range weapons than black holes are available, so it’s not like a black hole is the only weapon that can be used from a range that’s outside the planet’s defence systems. $\endgroup$
    – Mike Scott
    Commented Mar 16, 2022 at 18:53

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Black holes are quite heavy, the smallest one observed is 3.8 times the mass of the sun. So too move an average sized black hole would require an astronomical amount of energy, more than $10^{30}$J, which is more energy than the earth would make in trillon years, (if you are working with that much energy it would probably be easier to accelerate an asteroid relativistic speeds). Additionally even if the mass isn't initially a black hole, it would still take a large amount of energy.

An alternative solution could be to turn an object in the star system into a black hole. This could be done by launching a small black hole ($1,000,000$ Kg) into the object, the black hole would then "eat" the object, and grow into a larger black hole. Unfortunately this wouldn't increase the gravitational force from that object, so it wouldn't gravitationally destroy the planet, unless the black hole hit the planet itself.

But if a small black hole is fired into the star, as it "eats" the star, the gas would get compressed and heated as it falls into it, which would then ignite and explode, similar to a nova. The explosion would push a significant amount of plasma from the star into the space around the star, including the orbit of the planet, and considering how damaging a little bit of stellar palsma was (the electromagnetic effect would especially devastating to electrical effects), having a significant amount of such plasma through out the system would destroy the planet.

hopefully that helps.

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  • $\begingroup$ I dont think that accelerating a rock to relativistic speeds is a working strategy. You first need to find a good rock within a good distance of the target since you dont want to hit them in a couple of years time, build the accelerator on it, then accelerate it over a certain time period until it moves at the desired speed. Its likely that the defenders will track likely rocks and the acceleration method can be detected long in advance from lightyears distance. The attacker would need to protect the rock against deviating attacks or destruction by another rock for most of the journey. $\endgroup$
    – Demigan
    Commented Mar 16, 2022 at 11:42
  • $\begingroup$ @Demigan agreed that it is a technically challenging endeavor, but if their civilization is capable of moving black holes with masses greater than the sun and no solid surface to push against, then i imagine that it would be easier to put that energy into accelerating an million tonne asteroid to $299 792 457$ $ms^{-1}$ (which would have enough energy to tear apart a planet) . As to visibility/detection, if it was launched from alpha centauri at that speed, there would be only 0.4 milliseconds (the human eye takes 400 milliseconds to blink) between seeing it leave and it arriving at earth $\endgroup$
    – Nyra
    Commented Mar 17, 2022 at 0:04
  • $\begingroup$ being able to push a BH and launching relativistic projectiles are different things, especially if you want to accelerate a rock from Alpha Centauri to relativistic speeds towards earth. It takes time to accelerate that rock, if only to prevent the rock from desintigrating due to the acceleration forces. That means its going to take days, weeks or months to get it up to relativistic speeds, and that acceleration period is what can be detected for far longer than 0.4 seconds and is its weakness: place somethjng in front at a distance to either deflect it or splatter it and you are safe $\endgroup$
    – Demigan
    Commented Mar 17, 2022 at 5:20
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Frame shift: blacken their star (stealth Dyson sphere)

Graphene absorbs 2.24% of all light passing through it for each sheet of atoms present. To reduce the visible light reaching their planet by 50%, spin about 30 layers of graphene around the star (formally a Dyson sphere). The distance between sheets is about 3.3 angstroms, so you need a full 10 nanometers. It melts at about half the Kelvin temperature of the Sun, so you need to move it out a little from the surface, so take 6E18 (the Sun's surface area in meters) times 2. You also need to do this so it doesn't glow just like the star and provide useful visible light; at 3000 K it should glow dimly with heat that mostly bounces off the atmosphere.

So you need 1E-8 m x 6E18 m^2 = 6E10 m^3 of graphene, or about 60 cubic kilometers. Grab some comets and get to work! It'll be easier than making a black hole, at least. Note also an efficiency expert might not even make it a full Dyson sphere, just a little strip along the orbit of their star that is easier to keep in a stable orbit, which could cut this down to less than a cubic kilometer's worth. Focus more on repairing any damage they do to the graphene with bombs, and slaughtering them when they venture out from their defenses.

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  • $\begingroup$ What methods would you use to deploy those sheets undetected, and how do you protect them? They will "detect" what is going on when the sun's light gets dimmer, and then will either push it into the sun or try to destroy it. Assuming jets from the sun dont do a number on it. $\endgroup$
    – Demigan
    Commented Mar 17, 2022 at 5:27
  • $\begingroup$ I took this as a siege where the defenders are only safe within their defenses, so that their counterattack might be stopped. Additionally, a Dyson sphere of this type would be made by trillions of tiny fabricators; only the part actually damaged needs to be remade. If the enemy is sufficiently rambunctious, it might make more sense to slip in sunshields at random distances from the planet and maintain their positions actively until they are destroyed. $\endgroup$ Commented Mar 17, 2022 at 21:40
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Through some really intense stretching of quantum entanglement or hand-wavium perhaps. Star-Trek did recently with a Red liquid concentration of mass.

Problem is a black hole would likely destroy entire systems unless there was a way to set an expiration time on them.

Maybe long ranged Gravity crushing technologies? Though if they have that kind of power, destroying planets may become too easy.

Edit: Perhaps making the planet uninhabitable to life would be a more approachable solution than throwing a black hole at it. Perhaps find a way to slow the planet's orbit enough to have it orbit close enough to the home star to fry it, though it may collide with other bodies at that point.

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  • $\begingroup$ They want to destroy the entire system, collateral damage could be an issue. I was wondering if there was a way they could put a field up around the system, or some kind of device that would suck in all the matter and implode or smth like that. $\endgroup$ Commented Mar 16, 2022 at 0:38
  • $\begingroup$ I have to agree that when you have the power to erase star systems a very large can of worms is opened up. My belief comes out of suspension at “ humanity needs to permanently destroy an enemy planet.” Humanity is the bad guy now. $\endgroup$
    – Vogon Poet
    Commented Mar 16, 2022 at 1:41
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    $\begingroup$ It would not destroy the entire system. If we swapped our sun out for a black hole of equal mass, the planets would just keep spinning. The BH would simply act like anything as massive as itself, only with the energy of its evaporation as a problem for those around it. $\endgroup$
    – Demigan
    Commented Mar 16, 2022 at 9:16
  • $\begingroup$ Problem is, we're not replacing a star with a black hole of the same mass. We appear to be targeting a planet. One could argue that you'd replace the planet with likemass, but the addition of the planet's mass into an newly established black hole would likely be more mass in total than what was being replaced. $\endgroup$ Commented Mar 16, 2022 at 18:42

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