# How would one destroy a black hole?

Science-Fiction has tools to destroy anything: atoms, molecules, DNA, cellular organisms, multicellular organisms, buildings, streets, cities, countries, continents, planets, and even stars. Some extreme settings even have tools to destroy entire galaxies, and I know of at least one setting (Doctor Who) where they can destroy a whole universe and even the multiverse.

However, as far as I know, no scientist or writer has come up with a way to destroy a black hole. I'm not just talking about "wait for it to decay through Hawking Radiation"; I'm talking about "use this and the black hole just disappears in a reasonable timeframe.

Would such a method even exist? It can require unobtanium, obviously.

• Would having it merge with another black hole count? – HDE 226868 Feb 20 '16 at 23:51
• @HDE226868 Lol, I nearly put that. Considering you end up with one bigger black hole though I figured it wouldn't help :) – Tim B Feb 20 '16 at 23:53
• getting it spinning fast enough to have an equatorial escape velocity less than the speed of light. operation really big steelie. – King-Ink Feb 21 '16 at 0:27
• Its not a fully fleshed out answer, but: shove it into a wormhole and close the exit before it comes out at the other side, WHEN there is a delay in transmission in your universe. But even instant-transfer may work if you close it when half the hole is gone through. Repeat this until all parts are so small, so they will die thanks to Hawkin's Radiation... might take some time and patience, to be honest. – Confused Merlin Feb 22 '16 at 7:41
• atoms, molecules, DNA, cellular organisms, multicellular organisms, buildings, streets, cities, countries, continents, planets, and even stars. Heck, we might have the tools to destroy all of these... worldbuilding.stackexchange.com/questions/36103/… – fgysin reinstate Monica Mar 30 '16 at 8:58

Welcome to How to destroy a black hole for dummies

So, are you looking for a way to eliminate the right black hole, arent' you? Well, you're reading the right guide. But before beginning, it could be useful to make some clarifications on the nature of these galactic monsters. As Sun Tzu says, to defeat your enemy, you must first know him. Let's know what a black hole is.

1) Why black holes are a so formidable opponent?

Black holes are the natural enemies of all spacefaring races. With their bottomless capacity to consume all light and matter, it’s just a few septillion years before all things in the Universe have found their way into the cavernous maw of a black hole, crushed into the infinitely dense singularity. For a black hole, any matter entering the event horizon is added to the mass. Shoot bullets at a black hole, and you just make a slightly more massive, slightly more dangerous black hole. Detonate a nuclear bomb inside the event horizon, and you only make the black hole more massive. Fire your forward phasers at the black hole, and that’ll still make it even more massive. Swap those bullets in for lasers and black holes don’t care. Within the event horizon, energy and matter are one, and those very same black holes can convert that energy into mass. So all your projectiles and energy weapons inevitably just make it more dangerous. So the problem is that any material is introduced into a black hole (whatever is physical matter or energy) will be swallowed up and will contribute to the growth of the enemy.

What if I use an anti-matter weapon? Maybe throwing an antimatter black hole into a black hole? We'll have a nice KABOOM, and problem solved

Nice try Jimmy. The problem is that even if you manage to create and stabilize an anti-matter black hole (and it is doubly impossible, because first you have to find a way to contain antimatter, and then you have to find a way to contain an antimatter...black hole), throwing it at a black hole will surely create a huuuge explosion, but all the energy will be converted and processed by the black hole. The bottom line is: if a regular black hole and an antimatter black hole got black-hole-married in space, they wouldn’t vanish.

2) Solutions

So, what are the possibile solutions to destroy a black hole? The answer, surprisingly, lies in the enemy's very features. We must take advantage of the enemy's ability and twist them against it.

Wait

Yess...just wait. I know, it's the most boring one, but at least it's a solution. According to Stephen Hawking, black holes can actually evaporate over enormous periods of time. So, over an incomprehensible period of time, even the most supermassive of the black holes will have evaporated away into a harmless soup of particles. It turns out, in order to defeat the black hole menace, all we need to do is ignore them, and they’ll go away all on their own. But, if you asked how to destroy a black hole, I suppose you need it now. So, next solution is to...

Get rid of event horizon

Getting rid the events get two interesting results; first of all, you get what you want: you killed a black hole. In addition, once removed the horizon, you will have access to real black hole, and all its secrets. The problem is this solution is a bit complicated.

In general relativity, the mathematical condition for the existence of a black hole with an event horizon is simple. It is given by the following inequality: $$M^2 > \left(\frac{J}{M}\right)^2 + Q^2$$ where $M$ is the mass of the black hole, $J$ is its angular momentum and $Q$ is its charge.

Getting rid of the event horizon is simply a question of increasing the angular momentum and/or charge of this object until the inequality is reversed. When that happens the event horizon disappears and the exotic object beneath emerges. But that hides a multitude of problems. For a start, things with angular momentum and charge also tend to have mass. And in any case, the equation above describes a steady state. Feeding a black hole creates a dynamic state and there is no guarantee that the object will settle back into a steady state again without shedding the angular momentum and charge that it has been fed. In fact, the calculations are so fiendish that they have defied all attempts to tame them.

Use time travel device

Remember when we said that blacks holes in time dissolve? Sure, it takes eons, but what if you could speed up the time? Creates a kind of space-time bubble, and speeds up the time. The black hole will dissolve as expected, or perhaps even more quickly, failing its nourishment.

• You can't ged rid of the event horizon in the manner indicated. There is a maximum angular momentum that a bh can have. I can't explain why charging it doesn't work like a naive analysis would suggest, but that's a good question for Physics. – JDługosz Feb 22 '16 at 4:43
• "Perhaps more quickly" the Hawking Radiation figure doesn't count any new infalling material, so that's the quickest rate there. – JDługosz Feb 22 '16 at 4:44
• @JDługosz But the limit is physical or can be achieved though some unobtanium device? – Yaniv Feb 22 '16 at 9:20
• @JDługosz The physical argument for charging it goes along the lines that if you want to add more charge to your black hole you need to overcome the repulsive force between like charges. Otherwise the charge would simply be repulsed and rejected. At extreme charges near the extremal black hole this requires so much energy that when you manage to push the charge all the way inside you inevitably also end up adding a substantial amount of mass (E / c²), always enough to keep the inequality on the same side. That, and a similar finding for J, essentially forms the Cosmic Censorship Principle. – The Vee Apr 1 '16 at 0:28
• If you put a large enough amount of antimatter in one place, you don't get an antimatter black hole. You just get a black hole. Only charge, mass and angular momentum are measurable. No huge explosion when you introduce it to another black hole that was formed from matter. Well, no difference from introducing any other two black holes. It's a violent event but not due to the antimatter. – trichoplax Apr 27 '16 at 14:21

To visualize this concept, consider the rubber sheet model of gravity:

1. Spacetime is modeled as a taut rubber sheet.
2. Masses placed on the sheet cause a distortion in the sheet, causing nearby objects to fall towards each other (this models gravity).

Now, suppose we have an object of negative mass. Instead of pushing down on the sheet, it will pull up. This will cause positive-energy objects to move away from it, and other negative-energy objects to move towards it.

If we collide this negative-energy object with the black hole, its mass will be reduced by an amount equivalent in magnitude to the energy of the negative-energy object.

Note that this is all strictly theoretical, and the existence of macroscopic negative-energy particles has not been proven.

However, the physics behind this is very similar to Hawking radiation, which involves negative energy regions on the quantum scale.

Also note that negative energy matter is very different from antimatter, which has been proven to exist and has positive energy.

• Wouldn't such negative-mass object simply run away from the black hole? – Bojidar Marinov Feb 22 '16 at 13:48
• If they were both at rest, yes. You would have to accelerate the negative mass object to a sufficient velocity such that the repulsive force is insufficient to prevent the collision. – Runic-Scribe Feb 22 '16 at 15:54
• The repulsive force would equal the force normal matter would feel when approaching the black hole, right? And if this is so, it would require FTL travel (to enter) at the horizon... – Bojidar Marinov Feb 23 '16 at 10:35
• @Bojidar Marinov - Negative mass falls towards positive mass just like other positive masses do, see this article--the gravity generated by the negative mass is repulsive, but you can keep dropping in amounts whose own gravity is small compared to the black hole. And there is an exact solution in general relativity called the Vaidya metric in which a black hole is shrunk by negative mass dropping into it, see this paper (p. 4 notes "if black hole absorbs negative energy, black hole radius decreases"). – Hypnosifl Mar 30 '16 at 3:04
• However, although Runic-Scribe is right that negative mass could be used to destroy a black hole faster than it would evaporate by Hawking radiation, the idea that negative mass bends the rubber sheet "upwards" is wrong--see my answer here on the rubber sheet analogy, really it's only the shape of the curved sheet that matters, not its orientation in some higher-dimensional embedding space, so flipping over a model of curved space so that depressions would become peaks would be irrelevant. – Hypnosifl Mar 30 '16 at 3:07

The only way a black hole will ever disappear, as far as we know, is through Hawking radiation. Think of a black hole as a ball of energy. You don't destroy energy, we know that well, you just do stuff to it. Well, you can't do anything to a black hole, so regardless of what you throw at it, nukes, lasers, stars, etc., you will just add more energy to it.

If you have control of time, you could encapsulate the black hole in a localized time distortion in which time is accelerated, so that the black hole evaporates faster.

You could try and create your own anti blackhole with antimatter and collide the two, but we don't really know what happens to matter in a black hole, so you might just end up creating a normal black hole.

• I vote for antimatter. I also advise to get a front-row seat to see what happens, it should be a real once-in-a-lifetime experience. – Bookeater Feb 21 '16 at 11:35
• Antimatter wouldn't do anything except make the black hole bigger (and thus more stable). The no-hair theorem states that the only quantities measurable of a black hole are mass, charge, and angular momentum. – user14624 Feb 21 '16 at 23:50
• @Bookeater I doubt that would affect it at all, since the gravitation of the black hole would most likely affect the matter in such a way as to cause it to see to be "matter", also , nothing can escape the black hole , so even if you could destroy the singularity , the energy would just be sucked back down – user15036 Feb 22 '16 at 5:51
• As a dedicated Newtonian I just deny energy can add to a gravity well. – Bookeater Feb 22 '16 at 17:18

The problem is that once anything has crossed the event horizon it needs to be travelling faster than light to come back out - which is impossible with any known science.

So you either need to accelerate the mass to FTL speeds or reduce the curvature of space-time so that mass can escape.

However you do this I'm viewing it as being like puncturing a balloon, you create a breach in the event horizon and let the mass from the black hole pour out through it. The mass would jet away into space gradually reducing the size of the black hole until it is all out.

The breach can be explained using either of the mechanics I explain above - either you're forming a wormhole or in some other way accelerating the matter to FTL speeds or you're reducing the gravitational effect in a region so it's no longer a singularity at that point.

Doing this would require a LOT of energy, you need to overcome the gravitational force of the black hole to suck the matter inside it out or you're going to be violating several laws of thermodynamics.

• Also, c'mon, it's breaking the speed limit. :-) That's a tough one. – HDE 226868 Feb 20 '16 at 23:52
• Yep, hence the unobtanium. If they have FTL travel they already have that though. – Tim B Feb 20 '16 at 23:53
• Ah, I missed that. – HDE 226868 Feb 20 '16 at 23:54
• Yeah, the question didn't specify that they have FTL travel but most sci fi settings have it in some form and it did say unobtanium was allowed/expected. – Tim B Feb 20 '16 at 23:55
• That really doesn't make sense. The event horizon is a mathematical contour line, not something that can be "breached". – JDługosz Feb 22 '16 at 4:47

Can you convert a black hole into gravitational radiation?

The recently observed merger of two black holes converted three solar masses of black hole, or about 5% of the total mass. So what if you could place a massive object in close orbit around a black hole and feed energy into it to prevent it spiralling in to the black hole? That is a continuous gravitational wave source. The question I don't know the answer to, is whether it will be emitting more in gravitational radiation, than is being supplied to prevent inspiralling. If more, the black hole's mass is being converted to energy. If less, you have just found an exotic and inefficient way to make the black hole grow.

One for the physicists, I think!

Doesn't sound too difficult.

You need:
- Unobtanium hull (handwavium is also good)
- FTL drive (not the old-fashioned types that don't work in a gravity well, but a modern one)
- Suicide crew (or AI without self-protection circuits)

Enter the event horizon (the hull protects you from tidal stresses); approach the singularity and turn on the FTL drive. The ship and the singularity (where all the mass is) take off to the programmed destination.

You can't pass the event horizon without exceeding the speed of light, so we do just that. We program the FTL to rematerialize outside the Milky way, since what will arrive there is a naked singularity. This will cause all sorts of problems for the crew, but it will take thousands of years before they affect us. That'll be somebody else's problem.

• And how exactly does this destroy the black hole? – Nzall Mar 31 '16 at 19:26
• All known black holes contain a singularity and are surrounded by an event horizon [citation needed]. My technique separates them. One of the products is a naked singularity, I don't know a name for the other (it seems to be a massless event horizon and will likely vanish rapidly). – NL_Derek Apr 1 '16 at 21:28
• How does activating an FTL drive inside an event horizon remove the latter? – Nzall Apr 2 '16 at 8:21
• Granted, I'm being a bit tongue-in-cheek, I doubt if it's possible and I assume OP is asking for a bit of out-of-the-box thinking. However my thinking is that once the mass (which is all in the singularity) has been removed the event horizon will collapse to zero or (in some way) evaporate. Thus it will not "remove the latter [event horizon]" but an empty/massless event horizon is not a black hole -- QED. (Slightly) more seriously, I don't think my idea is significantly less plausible than the other suggestions. – NL_Derek Apr 3 '16 at 21:08
• Again, I do not see how activating a FTL drive inside the event horizon of a black hole has any impact on the black hole. Unless you're saying "use the FTL drive to remove mass from the singularity", in which case you should clarify that. – Nzall Apr 3 '16 at 21:46

The answer is to manipulate Hawking radiation. It is thought that "virtual particles" pop in and out of existence all the time in our universe, but generally they are anti particles of each other and instantaneously collide, and return to the vacuum (big handwaving paraphrase here to introduce the topic).

Near the event horizon of a black hole, the virtual pair can appear, but there is a chance that one of the particles is absorbed by the black hole while the other is ejected into the "real" universe. The black hole loses the mass and energy of the ejected particle, which is registered in the universe as Hawking radiation.

Since we want to make the black hole disappear, we need to induce Hawking radiation to flow out of the black hole at a much faster rate than normal. By much faster we mean orders of magnitude, since a solar sized black hole could take 2×1067 years to evaporate under natural circumstances.

Virtual particles appearing near a black hole's event horizon will need to be accelerated away from the hole in order to drain its mass. One possible way to do this would be to position something like a neutron star in close orbit around the black hole, just skimming over the event horizon. The powerful gravitational pull of the neutron star will rapidly accelerate any virtual particles away from the hole itself, and create a sort of "anti accretion" disc of now real particles streaming away from the hole in the wake of the neutron star.

The other thing for this to work is to ensure that there is little or no matter and energy in falling into the black hole. The neutron star could be used to transfer momentum of the material in the accretion disc away from the black hole during the period it is being manoeuvred into position, clearing the disc and preparing for the phase where it is "vacuuming" virtual particles away from the event horizon.

One could enhance the project by employing multiple neutron stars in tight orbits to strip away the accretion disc and channel virtual particles away from the event horizon. The amount of super science and technology needed to do this would be pretty mind boggling, though.

• What would stop the neutron star from itself collapsing into a new black hole once it had absorbed sufficient mass? – superluminary Feb 22 '16 at 12:50
• With sufficient handwaving, we are hoping that the virtual particles are being accelerated away from the black hole with sufficient velocity that they are not captured by the neutron star or star array. – Thucydides Feb 23 '16 at 1:13

## Temporarily suspend local gravity.

A black hole is a gravity bound, infinitely dense ball of matter. It holds together because the force of gravity is sufficient to overcome the forces pushing it apart.

If one had the ability to manipulate gravity, perhaps one has antigravity spaceships, one might potentially temporarily shut down gravity in a local region of space for a tiny fraction of a second.

I have no mechanism for how this might be achieved. This falls outside of any current physics.

## This would make a very considerable bang

It would be worth noting that this would likely create quite a big bang, probably on the order of a supernova. Large enough to destroy any nearby star system. Probably large enough to cook any planets within a few light years of the event.

• On the order of a supernova? I would think it would be a total conversion reaction--it would outshine a supernova by quite a bit. – Loren Pechtel Feb 23 '16 at 0:34

NovaLogic already got the right idea: The only known way to diminish a black hole is by using the Hawking radiation. But he did not given an implementation of an exploit. Here is mine:

The inverse Dyson sphere

You construct a Dyson sphere well out of the reach of the black hole's horizon. Than you cool down the inside of the Dyson sphere to be colder than the temperature of the enclosed black hole. At this moment, you start reducing the black hole by catching Hawking radiation from it and pumping it outwards.

Note that this method will be incredibly slow and it needs a lot of energy, too. But in the end, your black hole is destroyed.

P.S. In an always expanding universe, the cosmis background will become colder and colder, and all black holes will naturally die of this cause.

# Peer Pressure.

I fully expect someone to explain why this won't work (I'm guessing it'll be the divide-by-distance-squared part of the gravitational force equation), and that would be just fine.

But let's give it a shot.

1) Find a black hole that's only about 20 solar masses. This isn't a general solution, maybe after we pick off a few of the weak ones we can aspire to more.

2) Find several stars that are about 5-10 solar masses each.

3) Using your unobtanium power sources and some bored engineers, maneuver those stars into a globe centered around the black hole.

4) Carefully and synchronously move the stars closer to the black hole, not letting any of them get sucked in, until the stars are exerting more force on the matter inside the event horizon than the singularity itself.

5) If the matter won't come out yet (due to being pulled equally in all directions), shift stars around until enough net force is exerted in a given direction from the center of the black hole that matter previously inside its event horizon starts to move away from it again.

6) Figure out what to do with 4*10^31 kilograms of post-stellar matter.

• LOL! (And Welcome to Worldbuilding!) – JDługosz Mar 15 '17 at 2:09
• I'm not sure how the matter would manage to escape the black hole, though. It would have to be traveling faster than light, and that's not possible. – HDE 226868 Mar 16 '17 at 0:34
• Would the matter need to travel faster than light if the total gravitational force pulling it away from the black hole was greater than the gravitational force pulling it in? – Keith LaMothe Mar 16 '17 at 0:36
• @KeithLaMothe Yes, of course. – HDE 226868 Mar 19 '17 at 15:19
• In that situation, would it still be possible for the matter to move closer to the center of the black hole? – Keith LaMothe Mar 19 '17 at 18:42

I think antigravity would be the "simple" approach using common sci-fi devices. Hypothetically, we could have gravitons and anti-gravitons of some kind where the one cancels out the other. Then we just stream ridiculous amounts of antigravity towards the gravity, and eventually the black hole falls apart.

This presumes that A) your scientists find a way to create artificial gravity, and B) that negative gravity exists. And C) that you have a bunch of stars lying around with Dyson spheres you can use to power your antigravity beams.

So. Black holes are hard to approach. Time gets a little, shall we say, funky as you get closer. And then, of course, there's the tide. They'll tear a ship apart quicker than anything. I won't even give more than a cursory nod to the radiation, as we're all familiar with that. So, obviously, dropping some sort of magic bomb into the black hole won't work.

So, instead of trying to bring something to the black hole, we do the opposite. We bring the black hole to us.

Now, now, I know what you're saying. You don't move a black hole. And you're right. But think - We can create wormholes, right? We've been using them to get from place to place for a century now.

Only one problem. The wormholes only work one way. Generate one, put something in it, and it pops out the other end. What if I told you we found a way to reverse that? The generator, instead of creating the entrance, creates the exit? We've found a way - And while the maths of it are beyond me, Doctor Selene here will be more than happy to explain when I'm done.

So, we set up a generator and target it below the black hole's surface. The wormhole opens, and the black hole's own gravity pushes mass through. But, very quickly, that mass will be the entire black hole. At that point, we've only managed to move the black hole, and right on top of ourselves. Bad, right?

The solution is fairly obvious. Using a network of a few, let's say four, dozen generators spread across just as many systems, we use a quantum clock to synchronize them. They all open their wormholes at the same time, siphon off some of the black hole's mass, and close the wormholes before too much comes through. At that point, we have loads of what Doctor Selene calls exotic materials floating around ready to be harvested. Scoop them up, put them on some novelty keychains, and sell them in a gift shop, right? Oh, yes, the scientists will get their turn too.

It'd take a few cycles of this to completely remove the black hole, maybe a few months, but think of the rewards! Beta Three-Thirteen is sitting right in the middle of what would be a prime route between Caldari and Melantis. We'd see huge amounts of traffic between the two systems if we got rid of it! And I'm told the materials we'd be able to gain from the hole would be usable in dozens of industries!

We can do this, and we will do this. Now, I'll leave you Doctor Selene to answer the more technical questions.

# reduce the pressure with a tiny portal/teleporter

Teleporters or portal technology is pretty common in sf. You just use some additional dimensions to "fold" space (like I explained here) and punch a hole through space into the black hole.

You have to be careful though:
1. Only make a very tiny hole! If to much mass comes through that hole at once, it will just create a second black hole at the other end of the portal.
2. Aim the output-hole at empty space or something you want to destroy. You will get a constant stream of mass at a very high speed coming through.

But you also have some really neat side-effects:
1. You can power a big generator with the kinetic energy from that stream.
2. After you draw most of the kinetic energy from that stream, you can use the huge amount of mass to build a complete new stellar system or two.
3. You can fire the full power of that stream on an enemy battle fleet/base/planet
4. You can fire that stream roughly in the direction where you want to build that intergalactic highway, thus blowing away all that debris (planets, suns and stuff) to clear the way.

If that is to slow for you, you can use several tiny portals and direct the stream in different directions.
After a while, the mass of the black hole will have reduced enough, that it is just a big sun and the stream(s) will be reduced to a trickle of plasma from that sun. Now you can use your standard death star to blow it up and have some neat empty space.