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# Neutron star

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## Q: Is it possible for an artificial black hole to be created, or something that has the same effects? If so, how small could it be made?

Physicist: Not with any current, or remotely feasible technology.  The method in use by the universe today; get several Suns worth of mass into a big pile and wait, is a pretty effective way to create black holes.

In theory, all you need to do to create an artificial black hole (a “black faux”?) is to get a large amount of energy and matter into a very small volume.  The easiest method would probably be to use some kind of massive, super-duper-accelerators.  The problem is that black holes are dense, and the smaller and less massive they are the denser they need to be.

A black hole with the mass of the Earth would be so small you could lose it pretty easy.  Except for all the gravity.

But there are limits to how dense matter can get on its own.  The density of an atomic nucleus, where essentially all of the matter of an atom is concentrated, is about the highest density attainable by matter: about 1018 kg/m3, or about a thousand, million, million times denser than water.  This density is also the approximate density of neutron stars (which are basically giant atomic nuclei).

When a star runs out of fuel and collapses, this is the densest that it can get.  If a star has less than about 3 times as much mass as our Sun, then when it gets to this density it stops, and then hangs out forever.  If a star has more than 3 solar masses, then as it collapses, on it’s way to neutron-star-density, it becomes a black hole (a black hole with more mass needs less density).

The long-winded point is; in order to create a black hole smaller than 3 Suns (which would be what you’re looking for it you want to keep it around), it’s not a question of crushing stuff.  Instead you’d need to use energy, and the easiest way to get a bunch of energy into one place is to use kinetic energy.

There’s some disagreement about the minimum size that a black hole can be.  Without resorting to fairly exotic, “lot’s of extra dimensions” physics, the minimum size should be somewhere around $2\times 10^{-21}$ grams.  That seems small, but it’s very difficult (probably impossible) to get even that much mass/energy into a small enough region.  A black hole with this mass would be about 10-47 m across, which is way, way, way smaller than a single electron (about 10-15 m).  But unfortunately, a particle can’t be expected to concentrate energy in a region smaller than the particle itself.  So using whatever “ammo” you can get into a particle accelerator, you find that the energy requirements are a little steeper.

To merely say that you’d need to accelerate particles to nearly the speed of light doesn’t convey the stupefying magnitude of the amount of energy you’d need to get a collision capable of creating a black hole.  A pair of protons would need to have a “gamma” (a useful way to talk about ludicrously large speeds) of about 1040, or a pair of lead nuclei would need to have a gamma of about 1037, when they collide in order for a black hole to form.  This corresponds to the total energy of all the mass in a small mountain range.  For comparison, a nuclear weapon only releases the energy of several grams of matter.

CERN, or any other accelerator ever likely to be created, falls short in the sense that a salted slug in the ironman falls short.

There’s nothing else in the universe the behaves like a black hole.  They are deeply weird in a lot of ways.  But, a couple of the properties normally restricted to black holes can be simulated with other things.  There are “artificial black holes” created in laboratories to study Hawking radiation, but you’d never recognize them.  The experimental set up involves tubes of water, or laser beams, and lots of computers.  No gravity, no weird timespace stuff, nothin’.  If you were in the lab, you’d never know that black holes were being studied.