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Imagine a race whom have mastered the knowledge of black holes, at least a bit.
They've found a way survive, with their planet intact, inside the gravitation of the black hole without getting destroyed by it. (I know it is not possible for humans but in my fictional universe there are species which understand the universe a lot better then we do.)

Is there a way for the enemy to destroy the planets inside the black hole? I ask because all missiles or some cannon like the death star would be destroyed by the black hole and would the black hole also grow?

Let me explain the following picture: 3 planets are in the gravity pull of the black-hole but around each planet there is a safe-zone created by a much more advanced race, they even have something like wormholes in the safe-zone so they can leave the black-hole's pull. There is no way to enter the wormhole for other species.
If a planet gets sucked in by the black-hole, would the dismembered planet collide with the planets? I imagine the parts of the dismembered planet would rotate in a way people do in a funnel slide. I hope you grasp what I am trying to say.

Edit: JDługosz helped me understanding the horizon, please read his answer and make new suggestions.

  1. How can they find the localization of these planets?

  2. Which weapon would be enough to destroy them and what is the best way to destroy all three planets at once (So they can't prepare a defence)?

enter image description here

Would something like this hit the planets? But— I mean something with physical form, planets or a sun, but in the form of the example. Example

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    $\begingroup$ «something like this hit the planets» would a drawing of lensing effects hit the planets? Whaaaaaat? $\endgroup$
    – JDługosz
    Commented Sep 28, 2016 at 8:30
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    $\begingroup$ If they can enter end leave a black hole it means they operate outside our physical universe and/or possibly can move through higher dimensional space, so they can pretty much do anything and survive any attack you can think of. $\endgroup$
    – Bohemian
    Commented Sep 28, 2016 at 8:41
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    $\begingroup$ Why does your enemy want to destroy the planets in the black hole? Since nothing can ever come out of the black hole, it's already effectively as if the planets were destroyed -- they can never have any effect of any kind on the enemy. $\endgroup$
    – Mike Scott
    Commented Sep 28, 2016 at 13:23
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    $\begingroup$ The premise is incorrect, since there are no stable orbits inside of the black hole's event horizon, i.e. everything within must be falling into the center (though it could be spiraling around the center). I suggest you read up on the innermost stable circular orbit (for a non-rotating black hole this is three times the Schwarzschild radius). I also agree that give the premise, there is no way to give a true science-based answer. $\endgroup$
    – Snyder005
    Commented Sep 28, 2016 at 21:19
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    $\begingroup$ This question has way too much handwaving in the premise to be answerable. "There's a race that somehow avoids the fundamental problems with remaining near a black hole indefinitely, and can also somehow keep everyone else from using their wormholes. What happens when another object hits the unexplained planetary shells? $\endgroup$
    – Dan Henderson
    Commented Sep 28, 2016 at 21:48

13 Answers 13

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You need to understand better how the event horizon works. It is a point of no return. Your implicit idea of it being a shell that destroys anything that passes is simply wrong.

From physicist Matt Strassler’s blog:

A horizon is not an object, but a place beyond which escape is impossible. A famous analogy is to a boat approaching a waterfall, in an increasingly fast current. Once the boat passes a curve of no-return (see Figure 3), its engine will be unable to fight the current, and it will inevitably go over the waterfall. But the captain of the boat will not notice anything when crossing this curve; it is just an ordinary part of the river, whose importance will only become clear when the captain seeks to escape disaster. Similarly, in general relativity you will notice nothing when crossing the horizon; it’s only when you try to escape the black hole that you will discover that — oops! — you went too close

picture

A missile can enter the event horizon from the outside and hit the planet inside. They just need some way to aim when they can’t see in.

You can find examples of general relativity scenarios along the line of Alice falls into a black hole, and some time later Bob jumps in after her and can still rendezvous. Similarly, missiles entering the black hole can target the planets inside.

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    $\begingroup$ You are thinking of tidal forces? You don’t feel g forces like you are supposing. In free fall you feel none; to resist falling you feel a crushing force. Now tides are a problem, but this BH is the mass of galaxies for planets to exist inside the horizon; the forces will be smaller. Asimov wrote how the entire observale universe might be a black hole! And we have no trouble moving around; just (if that were the case) could not escape from the megacluster of galaxies. The larger the BH, the lower the average density. $\endgroup$
    – JDługosz
    Commented Sep 28, 2016 at 8:28
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    $\begingroup$ In this case Xxy is right, after a certain distance, things experience spaghettification, they will get completely obliterated and made a nice string of atoms. The effect is inversely proportional to the square of distance from the black hole. Thus if missiles are not getting destroyed, move your planets close to the center. This effect has no relation to the event horizon. $\endgroup$
    – Cem Kalyoncu
    Commented Sep 28, 2016 at 8:52
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    $\begingroup$ It's straightforward and direct, the physics supports missiles targeting the planets inside the black hole. Black holes can't act as a shields, even for planets snug in their safe zones. Plus one for cutting through the fog of physics. $\endgroup$
    – a4android
    Commented Sep 28, 2016 at 11:29
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    $\begingroup$ @Xxy the gravity effects get stronger as the object gets further past the event horizon. The time dilation effects get stronger too. And the velocity relative to the center, from the point of view of an external observer, approaches zero. So anything that enters the even horizon is doomed from an observer's POV, but the actual cessation of existence of that item will likely take millennia. $\endgroup$
    – Xalorous
    Commented Sep 28, 2016 at 18:14
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    $\begingroup$ «i still want to hear ideas of destroying something with my wrong vision of the black hole» that's not possible since we don't know what you were thinking your bh was like. And it’s completely made up so answers can just make up anything too. What you need, in a new question, is to describe your “exclusion zone” security field in detail and ask for ways around it. I’ll get you started with that shortly. $\endgroup$
    – JDługosz
    Commented Sep 28, 2016 at 22:03
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You should watch this video about black holes. Your premise is so nonsensical for General Relativity that you might as well be asking "why is the moon made of cheese?" Um... its not. Planets cannot orbit inside the event horizon, the only direction inside the EH is towards the singularity at the center. Everything inside will not retain a form recognizable to us. As @AnoE pointed out below, this applies after you are close enough to the singularity for tidal forces to tear you into a thin stream of particles, known as spagetiffication. However, just because an object can enter an event horizon and not be shredded immediately doesn't mean stable orbits are remotely possible.

Thus, the answers to your questions are actually trivial:

  1. How to find the localization of these planets.

The mass of these planets, along with all the rest of the mass of the black hole, is located at the infinitely small singularity at the center.

  1. Which weapon would be enough to destroy them and what is the best way to destroy all three planets at once. (So they cant prepare)

Nothing needs to be done, they are already destroyed.

You can't make this science-based, as your tag wants**. The only way to make your premise make sense is to move to an entirely different universe with different laws of physics, because Einstein, Hawking, and others have proven this impossible.

**Note: the question was tagged as science-based when I first answered this. That has since been removed. I'm not updating my answer since people seem to find it helpful, however the changed context makes it less relevant to the question.

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    $\begingroup$ This should be the accepted answer. Either go full fantasy style, ignore laws of physics and come up with whatever you like, since you already broke the rules, or play along the rules from the beginning. There are too many questions like "X is impossible, but I somehow allow it. How to achieve Y (which is next to impossible) without allowing it?" $\endgroup$
    – MatthewRock
    Commented Sep 29, 2016 at 9:27
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    $\begingroup$ @TheGreatDuck GR is incomplete to be sure, but we have a good understanding of where its weaknesses are, and the extreme curvature of spacetime inside the event horizon is not one of them (what exactly is happening to the matter inside, is still an open question). The only conceivable way to do this is to cause a negative curve in spacetime that opposes the gravity with some sort of negative mass matter (like is proposed for the Alcubierre warp drive ), but the existence of such is theoretical. $\endgroup$
    – Cody
    Commented Sep 29, 2016 at 19:55
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    $\begingroup$ @TheGreatDuck what you are talking about is in the realm of fantasy and fiction, not science. This question was originally tagged "science-based" when I wrote this answer, so the scope of my answer is within that constraint. Since other people address the fantasy aspects related to this, I am not amending my answer to account for that. What you propose is simply not possible, even in theory. $\endgroup$
    – Cody
    Commented Sep 29, 2016 at 23:01
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    $\begingroup$ @TheGreatDuck, “Perhaps there exists a particle that gravity does not apply to, yet has gravity”. That sounds like an oxymoron. $\endgroup$
    – Arturo Torres Sánchez
    Commented Sep 30, 2016 at 1:18
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    $\begingroup$ @TheGreatDuck yeah, that's a contradiction, unless you go around changing the definitions of things like "force" and "gravity". You can't interact with a field while also not interacting with the field. It goes beyond "not possible" to "not meaningful". $\endgroup$
    – hobbs
    Commented Sep 30, 2016 at 6:31
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The simplest method would be a sabot attack. If you hi-jack one of the enemies ships and know how it gets back to the home planet, it should be possible to plant a bomb/virus on there that knocks out the safe zone generators. Once that's gone, the planet gets sucked into the black hole.

Destroy one planet and you could well have a political/emotional victory. Faced with a third of their population (or the loss of their primary planet), they will need to negotiate an outcome. Losing a third of your resources (or centre of government) is pretty severe.

If they don't face up to defeat, the same thing might happen, or all outgoing ships might well get destroyed.

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  • $\begingroup$ That is a nice simple idea, a crew sacrificing their life, a planet destroyed in a second after turning of the safe zone, very cruel. The problem is after the first planet they would find a defensive also the enemy need to find the path for the wormholes maybe they can destroy 1 planet like that. $\endgroup$
    – Xxy
    Commented Sep 28, 2016 at 7:58
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    $\begingroup$ Black holes don’t “suck”. They have gravity like anything else. $\endgroup$
    – JDługosz
    Commented Sep 28, 2016 at 7:59
  • $\begingroup$ @JDługosz I was generalising for dramatic effect. The lack of the green zone would still result in the planet being obliterated by the black hole. $\endgroup$
    – user10945
    Commented Sep 28, 2016 at 8:05
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    $\begingroup$ I was puzzled about the phrase "sabot attack" as attacking planets inside a BH with wooden shoes shows ingenuity, but I couldn't help wondering about its effectiveness. Admittedly hurling millions of sabots at relativistic velocities into the BH might destroy the safe zone planets. Then I realised! What you meant was: "The simplest method would be sabotage." Throwing sabots or wooden shoes into factory machinery gave us the word "sabotage". Full marks for knowing the origin of the word. Plus one for the method. $\endgroup$
    – a4android
    Commented Sep 28, 2016 at 11:20
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    $\begingroup$ @a4android Well, I had another purpose for using that word. To me, a sabot is a container, carrier, or outer projectile for something explosive. The bomb here would be contained within a native ship and thus be hidden from view. $\endgroup$
    – user10945
    Commented Sep 28, 2016 at 11:25
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Science has no answers for you. We have no empirical way to test hypotheses about what happens inside an event horizon, so the best we can do is literally an educated guess. Steven Hawking recently made one of those guesses about what happens inside the first few nanometers, after years of work, and the scientific community is still debating the validity of his claims.

Your options are:

  • Spin the planet - A spinning black hole eventually loses energy to Hawking Radiation and gets smaller. Eventually such a black hole can dissipate. So, if you're patient enough to wait the quadrillions of years for it to dissipate, you can do something to the planets... if they're still there.

  • Subterfuge - Convince one of the members of that species to enter the wormholes and break down whatever magic is making this whole thing work.

  • Magic - This is one of those infamous "I invented a rock so heavy even God cannot lift it, now help me move it" sort of problems. You invented a technology which is so advanced that it literally operates beyond the known laws of physics. Use that same technology to attack the planets. When you invent rocks so heavy that even God cannot lift them, it is entirely plausible that said rock also cannot be lifted by science either. That's an inherent risk in such handwaving.

I highly recommend reading the blog post on Sanderson's First Law of Magic. What you describe qualifies as magic by Arthur C. Clarke's definition of magic, so you should plan around following Sanderson's First Law:

Sanderson’s First Law of Magics: An author’s ability to solve conflict with magic is DIRECTLY PROPORTIONAL to how well the reader understands said magic.

Sanderson's law doesn't limit the options you have for solving this issue, but it does point out that you're going to have to make sure the reader is very comfortable with it before resolving major plot points using it.

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Use Their Own Weapon

Your best bet is to learn how they maintain a planet inside a blackhole. Assuming equal technology/science level, your scientists and engineers most likely could reverse the method.

Espionage

If your race is far inferior in technology and you can't reverse engineer the method, then you try to capture a ship, plant some kind of a GPS/analytic device and send it back to analyze the road.

Antimatter Missiles

In theory antimatter doesn't destroy a blackhole completely but as far as we assume, big powerful antimatter missiles will create huge explosions inside the blackhole but even then the energy won't escape and the blackhole will grow larger.

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Cover the surrounding of the black hole with antimatter dust. The dust particles will fall into the black hole, and since they are everywhere, statistically some of them will hit the planets, and a matter-antimatter explosion even of a few grams of antimatter will release as much energy as an atomic bomb.

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You are facing the problem that the tidal forces of the black hole will destroy any missile you can throw at them. Thus the only solution I see is to throw a missile that is immune to tides--another black hole.

You still have the basically-impossible targeting problem of knowing where the enemy planets are hiding. However, you don't need a direct hit--all you need to do is overload the gravity generators that are protecting the enemy planets and their own black hole will finish the job.

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  • $\begingroup$ If you have a sufficiently large black hole (perhaps the size of the ones at the galactic core), the tidal forces will be minimal around the event horizon. Planets could orbit the singularity in the space between the event horizon and singularity, but the physical conditions in the space might not be conducive for biological life. $\endgroup$
    – Thucydides
    Commented Sep 28, 2016 at 19:31
  • $\begingroup$ @Thucydides Inside event horizon, space and time sort of "switch places", so you can't have orbits there without magic tech. As surely as time moves forward outside event horizon, everything inside moves towards singularity; there is no stopping or going back, any more than there is stopping or reversing time in normal space. $\endgroup$
    – hyde
    Commented Sep 28, 2016 at 20:17
  • $\begingroup$ @hyde But what about a rapidly rotating black hole? Don't you get a second event horizon, inside of which space & time have once again switched so an orbit would be possible? You'll still need some incredibly powerful gravity generators to keep the tides from eating your planet, though. $\endgroup$
    – Loren Pechtel
    Commented Sep 28, 2016 at 21:36
  • $\begingroup$ @LorenPechtel Right you are, I had forgotten that property of rotating black holes... hmm. $\endgroup$
    – hyde
    Commented Sep 29, 2016 at 3:38
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Find a way to divert a neutron star into the black hole. They are super dense already, and would add dramatically to the mass of the black hole, and would change the size of the black hole and the radius of the event horizon. Then the aliens planet would be actually inside, or further inside, and perhaps their technology might not be able to adapt to or overcome that difference.

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    $\begingroup$ Density has nothing to do with it, it is all about the mass. OP doesn't specify the mass of the black hole in which these planets "exist", but if it can encompass planetary orbits then it must be at least a few astronomical units across. A neutron star with at most 3 solar masses would barely make change in a black hole that size, already millions of solar masses. Moreover, stuff falls into black holes all the time. Even if there was a way to orbit inside a black hole, they would have to account for that or else be destroyed anyway. $\endgroup$
    – Cody
    Commented Sep 28, 2016 at 20:55
  • $\begingroup$ What about finding a way to divert a black hole to it them? Or grow a nearby black hole bigger? Im sure two black holes colliding would do something? $\endgroup$
    – user64742
    Commented Sep 29, 2016 at 19:51
  • $\begingroup$ @TheGreatDuck it would release a ton of energy as gravitational waves, gamma rays, x rays that would destroy whoever was outside sending the other black hole in. What happens on the inside of the two black holes is unknown. You can't simply "divert a black hole", the mass of a naturally occuring BH is at minimum 10x the mass of the sun, you simply cannot harness enough energy to move an object that size. $\endgroup$
    – Cody
    Commented Sep 29, 2016 at 20:06
  • $\begingroup$ No, I mean grow the smaller black hole by tossing a neutron star into it, and hope that the increased radius causes it to fall into the bigger black hole. $\endgroup$
    – user64742
    Commented Sep 29, 2016 at 22:05
  • $\begingroup$ @TheGreatDuck That would only have an effect on a similarly small black hole, which would have hardly any effect on the huge hole. Of course, if you have enough time, you could simply toss entire galaxies in the black hole, but it's unlikely you would have enough time anyway. We're talking on the order of millions or maybe billions of years - if you plan on such time scales, you can just ignore the threat alltogether - it will disappear on its own as the universe keeps expanding :) $\endgroup$
    – Luaan
    Commented Sep 30, 2016 at 11:45
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Only a god can kill a god

What you could use is the classical traitor scenario. If your alien race is so advanced, i higlhy doubt there is any way for an inferior race to take them in a frontal way.

So what humanity (or whatever inferior specie) need to destroy their planets is an inside man. Some kind of pariah from this advanced race who just happens to hate that much is own kind that he will help you gladly to wipe them out (did anybody said Avatar ?).

As far as how he would help humanity to destroy his own kind, i guess he could use his great knowledge in blackholes to create a small one within the safe zone of a planet. I'm pretty they wouldn't have planned that

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  • $\begingroup$ Nice idea but the problem is that this race is not like us. They remeber anything and they can use everything heard or watched, that is why this race is super advanced. But the race does not have a conzept of power or war, they live to study and understand the whole universe so they make experiments in the universe often destroying other species, and now some guys want to stop them playing around with us like we were insects. $\endgroup$
    – Xxy
    Commented Sep 28, 2016 at 13:44
  • $\begingroup$ So they are like very very smart and curious children ? $\endgroup$
    – yan yankelevich
    Commented Sep 28, 2016 at 14:14
  • $\begingroup$ Yeah and live is not important for them so if they try something out in the universe sometimes other races die, so they have to stop them. They understand the act of war but for them is it pointless, they dont have an army or weapons, they seek for something bigger. $\endgroup$
    – Xxy
    Commented Sep 28, 2016 at 14:27
  • $\begingroup$ So maybe you can paradox them out to hell ? Tell them humanity knows something bigger, way more badass than anything they could have encountered in their seek for knowledge. But to got this they have to give humanity some kind technologies that we could use to destroy them. Obviously you don't tell them that you want technology X to destroy them, just that you want it for reasons. As they don't trust in war they won't think of humanity using this set oftechnology to get them out. $\endgroup$
    – yan yankelevich
    Commented Sep 28, 2016 at 14:32
  • $\begingroup$ That would be a way but i think a race like that would not be so easy to fool. Even fooling a human like this is difficult, fooling such a race would be huge. They dont talk to us also because we are not important for them. $\endgroup$
    – Xxy
    Commented Sep 28, 2016 at 14:36
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No one knows what exactly happens after you pass event horizon (which is just outside the black hole, which is point of no return. Since it's point of no return we don't know happens inside).

Most likely enemy missiles will transform into information or some kind of dense mass(energy) before hit your planet which is inside event horizon. So enemy can't aim or destroy your planet. Not only that they'll never know if they hit the target or not after random attack. Of course in case enemy master same technology as yours then can send probes into inside event horizon then they can aim and send missile that withstand even horizon.

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  • $\begingroup$ Note that once anything crosses the event horizon, it is expected to be traveling faster than light and therefore moving back in time instead of forward. What could withstand this time reversal? $\endgroup$
    – user6030
    Commented Sep 29, 2016 at 20:14
  • $\begingroup$ @user6030 Umm, I'm not sure why you would think that. The topology of the spacetime is simply such that there is no path forward in time that leads out of the black hole. That says nothing about the speed you'll have inside the black hole (relative to what?). The black holes we're observing certainly don't appear to be accelerating the infalling matter to anywhere close to the speed of light (though obviously, we only see what's outside of the horizon), and I don't see any reason to believe that would happen, much less faster than light travel, which doesn't fit GR at all. $\endgroup$
    – Luaan
    Commented Sep 30, 2016 at 11:38
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If you want to mix magic and popular physics, introduce the idea of gravitational wave 'earthquakes'. The people on those planets may be magically protected from a constant gravitational field, but a gravitational wave disturbs that constant field and squashes the planets into egg shapes, causing earthquakes, eruptions, etc.

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Chuck another Black Hole at it.

First of all, technology that can protect an entire planet from the harsh environment of a black hole (not to mention the extreme gravity!) must be pretty sweet. All infalling matter would have already been accelerated to relativistic speeds by the time it got to the planet. Basically, a missile (even an antimatter one) would be nothing compared to what the planets already encounter every day from just in-falling dust and extreme blue-shifted radiation.

Now, if its possible at all to destroy these planets, colliding the blackhole with another blackhole just might be able to crush these planets. If we assume that the black hole in your diagram can fit 10 earths side by side inside it, and we use a formula from Wikipedia, we can compute that your black hole has a mass approximately equal to 27,000 solar masses. This is about 1/4 the size of the smallest super-massive blackholes. In the black hole collision detected last year, about 4.6% of the mass of the two black holes colliding was released. If we chuck another black hole similar to the size of the black hole in your diagram at it, and we assume a mass loss of 1%, 540 solar masses of gravitational energy will be released in the collision. For the sake of your aliens, I hope that their gravity shields can protect them from that much energy.

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My answer is specifically based on Destroying the planet thus in any manner we will not be able to visit or colonize the planet afterwards. If we can somehow simulate an experiment which increases the hawking radiation on event horizon the black hole will eventually lose mass and destruct. Exponential growth of particle and antiparticle pair creation will speed up the process.

Hawking radiation (Wikipedia)

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