# Artificial gravity with high density [closed]

Could a very small, dense, object (sort of like a neutron star) be used as artificial gravity in a spacecraft of some kind? the size of the spacecraft or cost/difficulty of making such a thing does not matter here

• erm... I can understand your spacecraft needs artificial gravity but why do you have to drag a star with you? ;D Commented Nov 8, 2017 at 2:38
• When you say like a neutron start you just mean some material that is incredibly dense, right? Commented Nov 8, 2017 at 3:58
• The author and physicist Charles Sheffield had spacecraft with plates of ultradense matter as sources of artificial gravity in his The McAndrew Chronicles (1983) and the expanded edition The Compleat McAndrew (2000). Robert Forward speculated about applications of ultradense matter as gravitational machines. Yes is the answer it could work, assuming the practical difficulties of moving extremely dense matter can be solved. Commented Nov 8, 2017 at 4:29
• No, because close to such a thing, the gradient in gravity will be very large. I wouldn't want to walk with my head in 1g and feet in 20g.
– Karl
Commented Nov 8, 2017 at 6:04
• The Collapsium by Wil McCarthy discusses a question similar to this: material of arbitrarily huge density, but no intertia Commented Nov 8, 2017 at 13:46

Assuming that the OP is just wanting to use some sort of material with similar density to a neutron star to provide gravity based acceleration.

So, the equation for gravity in a non-relativistic setting is F=G*m1*m2/r^2, where r is the distance between objects, m's are the masses, and G is the gravitational constant (6.67408e-11 m^3/kg/S^2). In your case, we just want to get some acceleration, not the force on your object. Happily, the force on that object is F=ma, which let's us cancel the m of the object from both sides of the equation, giving us a=G*m/r^2. For a given radius r we can solve the needed mass m for some desired a.

For example, let's say you have a big ship with a 1km radius to the living area. Here you want a reasonable gravity field, say 1/3g (3.26m/S^2). We plug and chug to find that the required mass would be a huge 4.9e16 kg. Moving such an object with any propulsion system would be a feat, but if you can neutron matter or similar superdense stuff to make it fit in a reasonable space, I'll assume that you have that covered.

The real problem you run into here, however, is the radius issue. In the previous example using that mass but adding 100m to r decreases your acceleration by 20%. Halving the radius increases a to 13m/S^2, a near 400% increase. While you may be able to get this mass, controlling your distance from it will be extremely important!

The short answer is not really
...Depending on how many problems you want to hand wave away.

• Problem 1 a neutron star is still quite big typically around 10km across - not that handy for a space craft.
• Problem 2 a neutron star could weigh as much as the sun or more – not that handy if you want to go anywhere in the space craft.
• Problem 3 you could not get too close as the gravitational forces would be enormous close in.
• Problem 4 neutron stars are usually accompanied by intensive magnetic fields and rotate rapidly and generally behave in a way not conducive to being inside or near a space craft.

No doubt others would be able to think of additional issues.

• In short, technically it can be used, but it will create many more problems. Commented Nov 8, 2017 at 2:09
• If you want to schlep the thing along in a wagon, or with chemical rockets, it would be hard. Something that massive has a lot of inertia. But if you moved by space warps or something that could be cool. You would actually not move the starstuff ; you would bend space so your starstuff ended up in a new place. Commented Nov 8, 2017 at 3:02
• Strictly speaking, the OP didn't ask about bringing a neutron star along. The question about something like a neutron star, or in its words "sort of like a neutron star" as a dense source of artificial gravity. Commented Nov 8, 2017 at 4:15
• @a4android Well it depends on what the other properties of the thing that is "sort of lika a neutron star are". If they are all like a neutron star then no as above. If they are like something else then maybe. The basic problem (hand waving everything else) is that an intense gravitational field will produce a much steeper gravity well. Commented Nov 8, 2017 at 9:39
• Most of the problems from whatever properties the super-dense material have been hand-waved away. However, your point about the steeper gravitational gradient. Charles Sheffield's McAndrew stories (see my comment to the question above) has a large plate of ultradense matter for artificial gravity. Crew quarters could be moved either closer or further away to compensate for acceleration. I'd be worried about ultradense matter changing phase explosively. But we can assume it won't. Its mass should be the equivalent of a small asteroid (at least). Commented Nov 8, 2017 at 11:46

Well....

You can use mass to provide acceleration to mimic Earth conditions (Earth does). With more density you get away with less mass than the Earth, in fact you'd get a advantage of several orders of magnitude with neutron star densities.

But that's still much more mass than a space station; more like a small moon.

• True, but having a small sized chunk of neutron matter would be explosively dangerous as it would want to become ordinary matter again. That said if you can use some form of force filed to contain it then why not? You could then turn the force field off at the destination and generate yourself a moon sort of "flat pack" style. Commented Nov 8, 2017 at 15:22