# How would someone destroy a black hole that’s at the centre of a planet? [duplicate]

For starters, the black hole is temporarily contained. But once it’s containment fails it will devour the planet. Obviously, that’s a bad thing. What’s a reasonable way to prevent that?

Also the black hole is currently really tiny. Like 4 feet in diameter.

It can be an outlandish solution as long as it would have a chance to work, and would not take long to implement

Thanks.

• How did a black hole get in the center of a planet in the first place ? How it got there could relate directly to how to get it out of there. What's the planet made of - it's internal structure ? What tech level exists - e.g. could they "simply" dig a hole five feet wide to the center of a solid code and keep the tunnel from collapsing long enough to move the black hole ? The mass is also too large as pointed out others. Jul 14, 2019 at 1:11
• This question reminds me of that Stargate episode. And I wonder if it would have the same effect with time that the show had? Jul 14, 2019 at 1:54
• A 4 feet black hole is in no way tiny. It's humongous!
– vsz
Jul 15, 2019 at 4:16
• @R I did not mention the internal structure of the black hole, I mentioned the internal structure of the planet. Jul 15, 2019 at 7:39
• Possible duplicate of How would one destroy a black hole? I asked this question already a while ago. Could you indicate why that question does not provide you with any answers? Jul 15, 2019 at 14:41

A black hole with a Schwarzschild radius of 4 feet would have a mass of 137.5 x Earth and the gravity to go along with it. Such a black hole would instantly liquefy the earth as it shreds it into an accretion disk and shoots gamma rays straight through the earth's poles.

There would be approximately 0 seconds for a committee to consider the problem before being vaporized, thus no solution will be found.

For narrative purposes however, the author might wish to reconsider the mass of the black hole to one that is less instantly catastrophic using the following: calculator. For instance, a black hole with a mass of 72135 metric tons would have a radius of 0.0001071103 femtometers and a lifetime of approximately 1 year before it goes critical and destroys the planet.

Such a black hole would be too small to interact with any atom inside the earth, so it would float freely, ping-ponging back and forth without ever acreting any more mass. A literal ticking-time-bomb if you will as it passes in and out, in and out through the Earth.

• @Zeiss In my example it would release energy of 1.6e16 calories per second. Enough to heat 1.6e13 kg of water 1 degree per second. However the mass of the earth is 5.9e24 kg so it should resist heating up that much for a good long time. Jul 14, 2019 at 0:54
• If the black hole evaporated completely due to Hawking radiation, I don't think the intense burst of radiation at the end of its life would be enough to blow up the planet--this abstract of a Steven Hawking paper says in the last 0.1 seconds it would emit energy of 10^30 ergs = 10^23 joules, equivalent to about a million 1 megaton nuclear bombs, which would be a huge amount on the surface but I'm not sure how much we'd feel it if it happened at the core. By comparison, I've seen an estimate that says it's take about 10^32 joules to blow up the Earth. Jul 14, 2019 at 3:04
• Also, the question said 4 feet in diameter, not 4 feet in radius. A Schwarzschild radius of 2 feet would mean a mass of 4.105 * 10^23 metric tons, the Earth's mass is 5.97 * 10^24 kg or 5.97 * 10^21 metric tons, so the black hole would be about 68.8 times more massive than the Earth. Jul 14, 2019 at 5:31
• @Hypnosifl I was typing up a reply to disagree with you, but after calculating you seem to be correct that it's not enough energy. So I asked the question here instead: physics.stackexchange.com/q/491536/232868 Jul 14, 2019 at 6:47
• @Hypnosifl Even that much mass would do truly terrible things to the planet.
– Ash
Jul 14, 2019 at 10:45

Feed the hole negative mass.

Probably you have some negative matter around to power your Alcubierre drive. Load that into your little black hole. You will need a fair bit to make a difference.

To my surprise, this is apparently a done thing in theoretical circles: adding negative mass to model the shrinking of a black hole via Hawking radiation.

https://physics.stackexchange.com/questions/153376/what-would-happen-if-a-negative-mass-crossed-the-event-horizon-of-a-black-hole

The situation of negative mass falling into a black hole does have one important consequence though, in GR it's the only way for the event horizon of a black hole to shrink rather than expand, and for this reason a dynamical black hole metric (the Vaidya metric) with negative mass falling into it is sometimes used when trying to model the long-term behavior of a black hole that is "evaporating" due to continually emitting Hawking radiation (since this is a quantum effect, and general relativity is not fully compatible with quantum mechanics, this evaporation should ultimately require a full theory of quantum gravity to model it completely accurately, but it seems reasonable to expect that the earlier stages of evaporation, before the size of the black hole and the energy density approach the Planck scale where quantum gravity effects are expected to become significant, should have some close analogue in classical general relativity).

• Bad idea. Really, really bad idea. If you feed a black hole with positive mass, you reduce its Hawking radiation, making it more stable. If you feed it negative mass, you increase its Hawking radiation, pushing it further on the exponential path that will make it explode with the force of many, many atomic bombs. And the black hole becomes impossible to feed long before it blows up. Trust me, the last thing you want to do is sit on a black hole that's too small to feed. It would be like sitting in a submarine that's slowly sinking into the Mariana Trench with no means to stop its sinking... Jul 14, 2019 at 17:49
• Why not just put it in a handwavium box which shields against gravity? That's no more outre than negative mass! Jul 14, 2019 at 19:41
• @cmaster - See the comment by WetSavannaAnimal on the OP, if the exploding black hole releases about the same amount of energy as the asteroid that killed the dinosaurs, it seems unlikely it would cause devastating effects since even that much energy on the surface didn't break up the crust or turn it molten or anything, the harmful effects were mainly from the soot and there's no reason to think an explosion 6371 km underground would kick up soot in the same way. You might get big quakes and tsunamis, but a civilization with the tech to make negative mass could probably find tech solutions. Jul 14, 2019 at 20:57
• @Hypnosifl The OP's black hole is so big it'll immediately turn the planet into an accretion disk. The people on that planet won't stand a chance to even realize that they are dying. My comment assumed that the black hole was scaled down to manageable levels in the first place. With black holes it's either that they are so small that you constantly need to feed them to avoid blow up, or that they are so stupendously heavy that nothing must get near them to avoid being torn apart by their tidal forces. Pick your poison. Jul 14, 2019 at 21:16
• @cmaster - Yes, I wasn't talking about the OP's exact scenario, just responding to your comment that feeding a more-reasonably-sized black hole (say, one with a radius of 0.1 mm) negative mass to shrink it would be a bad idea. My point is that although this would cause the black hole to blow up, if it would only release about as much energy as the impact of the chicxulub asteroid (in fact a little less than the asteroid, but same order of magnitude), then given that it'd be at the center of the Earth rather than the surface I don't think the consequences at the surface would be too terrible. Jul 14, 2019 at 21:30

I will assume you want something vaguely scientifically plausible. (I will also assume when you said "small black hole" you really meant one that is small enough to be contained on the surface of a planet and that the 4' size was not what you really meant.)

To start with, you can't destroy black holes. You can -- with difficulty -- move them. You can feed them and make them more massive. You can charge them and change their spin. But that's about it. So pretty much all you can do is try to get it up out of the planet, and that requires as much thrust as it would to launch the same mass of ordinary material into orbit and a way to apply that thrust to the BH.

(It's true that BHs probably evaporate due to Hawking radiation (though it's never been observed), but if HR is real, evaporation takes a very long time.)

The only way moving the BH might be doable (which wouldn't necessarily destroy the planet as a side-effect) involves charging the BH and then using electromagnetic fields to accelerate it. Pretty hard to do!

That brings up the question of the BH's mass. If it was temporarily contained, then it must have had a large charge and been supported by EM fields. It's mass is its mass, and if it was a small BH -- say the same mass as a mountain -- the containment facility would need to be able to support that mass concentrated into a really, really tiny object. The Schwarzschild radius of a BH of 100,000 tons (which would be very difficult to support with any imaginable technology) would be about 10-19 meters which is roughly 1 millionth the diameter of a proton.

Something that small would find it very difficult to swallow anything, so while it would orbit inside the planet, it would grow only very, very slowly. It would probably come to a halt (due to dynamical friction) at the planet's core and just sit there growing very, very, very slowly. It would probably have no effect whatsoever on a thousand year timescale.

The bigger the BH, the more of an impact it would have, but the less likely it would be that it could ever have been contained at the planet's surface.

• I seriously doubt that it's possible to impart a meaningful charge on a black hole: Any charge you add to it will be carried away by the hawking radiation rather quickly. Yes, it may absorb many billions of electrons, but the OP's black hole is many times heavier than earth. I guess, by the time you have it charged enough to be able to move earth relative to it, it will be spitting out its charge much faster than you can add charge to it. Jul 14, 2019 at 17:55
• @cmaster - There's an equation for the rate a charged black holes loses charge via Hawking radiation in this paper on sci-hub.tw, see equation (7) on p. 1144 (there's also a simpler approximate equation (9) but it only works when the black hole mass is significantly larger than 1.7 * 10^5 times the sun's mass, so it won't work for small black holes). Someone could use it to figure out the rate you'd need to fire charge in so it'd be greater than the rate of charge loss. Jul 15, 2019 at 17:49
• Unfortunately, I don't speak Russian, so that paper is out-of-reach for me. Nevertheless, for black holes of stellar weight and more, charging them is no problem (ignoring the amount of charge you need to allow electrostatic manipulation) as they have negligible hawking radiation. It's the small, hot black holes that you might stand a chance to move if they were charged, which you cannot charge because they radiate their charge away. Jul 15, 2019 at 18:34
• @cmaster - the paper is not in russian, the sci-hub site will usually have a captcha test where the explanatory text is in russian but you just have to type the word you see in the graphic and then hit the big button. Technically it's a pirate site but it's widely used by scientists. Anyway, if you haven't done a calculation with an equation, how do you know the BH will radiate its charge away too quickly to do useful things like using its charge to transport it a distance similar to the radius of the Earth? Jul 15, 2019 at 21:00
• @Hypnosifl Ah, well the captcha seems to have got stuck in my uMatrix - I only saw some Russian text... Anyway, have you ever tried levitating something by charging it? Unless the thing you are levitating is very light-weight, there's no chance to be successful. Not because the electric force is too weak, but because it's so strong and there are strongly charged particles everywhere which move to neutralize it. Ok, you can put your black hole into vacuum, but once the Hawking radiation becomes hot enough to include electrons/positrons, any charge will skew the emission rates, and soon be gone. Jul 15, 2019 at 21:34

For something that sounds plausible, but totally isn't

Fire charged particles at relativistic speeds on tangents to the event horizon. And just before they cross the event horizon, slow them down to below relativistic speeds with bursts from powerful magnetic and electrical fields.

As they near the black hole, their induced mass creates gravitation fields to compete with the internal mass of the black hole. By firing multiple particles simultaneously at antipodal targets tangential to the event horizon, the black hole can't move so its internal mass it stretched between the equal gravitational forces pulling it apart.

By this means, tiny bits of matter can be teased away from the grip of the black hole.

Keep it up until it is too small to hurt the planet.

Scientists save the world, again. Your welcome.

• Sorry, but this won't work. The event horizon is really a point of no return, with the only exception of hawking radiation. Also, there's no such thing as "its internal mass it [sic] stretched between the equal gravitational forces". A black hole really behaves like a single dot of mass from any outside point of view. It cannot be deformed. You can deform the event horizon, as happens during black hole mergers, but that is purely an effect of spacetime around the black hole. The black hole itself keeps behaving as a single dot of mass. Jul 14, 2019 at 18:03
• @cmaster, please note the science-fiction tag and the opening clause of my answer -- its only meant to sound good. Of course, it won't work.
– EDL
Jul 14, 2019 at 18:26
• Ok, I may not be the best audience for soft scifi as I've got quite a bit of physics training. And indeed, you say it's not plausible. Unfortunately, my downvote is already locked, so I can't remove it unless you edit your answer a bit. Nevertheless, the "sounds plausible" definitely does not extend to physics students. Jul 14, 2019 at 18:41
• @cmaster Could we reverse its polarity? Jul 15, 2019 at 12:16
• @Sentry Sorry, didn't understand your comment. Reverse the polarity of what? Jul 15, 2019 at 16:45

A black hole with an event horizon circumference of ~13 feet (circumference because diameter is meaningless in a region of space so deeply curved) would mass far more than the Earth. The surface gravity of an Earth-sized planet with such a body at its core would be well beyond survivability of any land animal less tough than a small spider or insect (though aquatic creatures would be okay until they tried to dive too deep -- say, more than about ten meters).

So, don't worry about destroying that four foot black hole. Everyone will be dead before it's known why the Earth is being swallowed -- and it'll never get near the center of the planet; it'll tear the whole planet up before passing without a noticeable change in trajectory.

• diameter/radius is not meaningless, you just have to select a coordinate system, usually using the radial coordinate of Schwarzschild coordinates...I explained the physical meaning of the Schwarzschild radical coordinate here, it's defined by measuring the area and then using the standard relation Area = 4 * pi * radius^2 Jul 14, 2019 at 5:02

Spin it up until its angular momentum becomes sufficiently large that it becomes a naked, toroidal singularity, at which point the laws of physics metaphorically throw up their hands and shrug in confusion.

• Which will instantly annihilate earth in a giant burst of gamma radiation... Jul 14, 2019 at 18:04