A question came up recently about how sound would travel through a neutron star (as it does)...

Well, not a neutron star as such but through a material like 'neutronium'. Assuming one could stand on the surface of the object and shout at it or whack it with a spade or something (without unfortunate side effects such as a squashy death etc. etc.), would the resulting sound wave:

1. Do nothing as the material is too densely packed and stiff so the wave wouldn't propogate?
2. Be the perfect propogator of the sound?
3. Something else?

I would imagine (I'm guessing) it would be a perfect sound medium. All other problems aside.

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I wonder if you could generate a fountain of material this way.

Imagine a large object moving near lightspeed. It hits the neutron star. At the antipode--would the quake exceed gravity and cause degenerate matter to fountain out high enough to be caught?

A neutron star is the core of a star of between 1.4 - 3 solar masses compressed down to something with a diameter of around 30km. Thats quite dense and if you would trow an object big as pluto at it I dont think it would move much at all. What probably would hapen is that the object (with bigger size and alot less mass) would shatter completely and probably becone a part of the star sooner or later..
Remember, the neutron star is so dense so that something as big as an olive would probably have the weight of around 100 000 000 000kg.. Try to knock something like that around...

On the other hand the neutrons are so well compressed they are in a state where they have no friction what so ever. So.. I dont really know if there would be any sound from something as light as something small enough to not justshatter would be..
But.. Even though something as a collision with some object (not even in range of its own mass) probably would not make much sound there are things that probably can make soundwaves that can be heard on the whole neutron star, and that is quakes. The quakes are like our earthquakes here on earth were the plate tectonics move on top of eachother. On a neutron star the highest layer can sometimes not keep up with the cores rotation speed, and it becomes like a quake. The result is that the neutron star get some glitches in its rotation speed. The quakes, if something, would probably make a sound

So.. Sound on a neutron star? Yes probably, but throwing a pea on one side of a mountain doesnt make sound enough so you can hear it on the other side..

Wiki has something to say on speeds in solids...see:http://en.wikipedia.org/wiki/Speed_of_sound

pete

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A second rate theory explains after the fact.
A first rate theory predicts.
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well, if Bob Forward, a theoretical physicist, got it right, then yes, a Cheela can communicate long distance (i.e. an awful lot of millimeters) by drumming on the surface of the neutron star.

What keeps the neutron star from becoming a black hole? I think it's "neutron degeneracy pressure" so it should be possible to set up pressure waves in the neutronium--two neutrons squeezed together, they spring back apart, pushing against another neutron, which springs back, leading to the chain reaction known as a "wave". In fact, as someone said, it would be the perfect medium for conducting sound--with very little separation between the neutrons, the wave would be like (or even better than) an electric wave in a conductor and go nearly the speed of light.

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Todd (Bowie, MD, US, North America, Earth, Sol System, Vega region, Local Bubble, Orion arm, Milky Way Galaxy, Local Group, Virgo A Cluster, Virgo supercluster, the universe in which spock is clean shaven)

Quidquid latine dictum sit, altum sonatur.

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tdvance. A similar such concept, magnons, ...waves of spin was used by Leinson and Oraevskii to add sufficient energy to from a forming pulsar, to cause the supernova to actually "go"...circa 1988, Sov. Journal Nuclear Physics.
see:http://adsabs.harvard.edu/abs/1989PZETF..49...65L

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A third rate theory forbids.
A second rate theory explains after the fact.
A first rate theory predicts.
A. Lomonosov

Except neutronium is not a solid, it is a superfluid.

But I think tdvance is right about sound waves in it.

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If I understand correctly, the equation of state for a neutron-degenerate gas (= "neutronium" in SF parlance) is poorly known. But the neutron degeneracy implies individual neutrons have effective velocities close to that of light, so I can imagine the speed of sound through such a degenerate gas would also approach lightspeed. Could be wrong, though.

Grant Hutchison

1: The speed of sound in any medium will increase as the material's stiffness increases. A material can't be "too stiff" for waves to travel in, although what happens when the predicted speed of sound (which is, more pedantically, the speed at which infinitesimally small pressure waves travel through a medium) gets great enough for relativistic effects to be significant makes my head hurt.

2: What do you mean by "perfect propagator?" Lossless?