Neutron Star core

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Summary:

Do millisecond Neutron Stars cavitate in their cores?

Main Question or Discussion Point

I have a question regarding Neutron Star cores that perhaps PF could clarify for me. Given a millisecond spinning NS, and given that its gravity decreases toward the center, being a spherical body, does centrifugal force displace the core material outwards to form an empty obloid-shaped cavity in the star's center?

Also, if a spatial cavity would in fact result, what theoretically would it "contain" or consist of? Normal spacetime vacuum or something more exotic perhaps due to severe frame dragging and relativistic effects?

TIA
 

Answers and Replies

Janus
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Even if gravity itself diminishes as you approach the center, the pressure due to the weight of all the material further from the center increases. In addition, the material aligned along the axis of spin would not have any of that pressure mitigated by the spin and would only be pulled in towards the center by gravity.
 
jim mcnamara
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The neutron core could (hypothetically) be quark matter. Strange quark stars may have been observed
https://arxiv.org/abs/1508.07745 --
Therefore, we conclude that such an ultra-energetic supernova provides a possible signature for the birth of a strange quark star.

I mentioning this because you made some assumptions about neutron stars. Perhaps quark matter is worthy of some consideration in your context.

NB: I am no astrophysicist. Corrections welcome.
 
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The link below doesn't address the cavity portion of your question, but it does address extremely rapid pulsar rotation and centrifugal force. I don't know if this theory could be reconciled with Janus' comment (his statement would seem to rule out a blitzar being possible), but here it is anyway...

https://en.wikipedia.org/wiki/Blitzar
 
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Generally, bodies that rotate at constant angular velocity do not cavitate at centre.
The reason being that although centrifugal force is mv2/r, it is mω2*r. Gravity decreases inwards, but so does centrifugal force. If centrifugal force does not exceed gravity at surface, it will not exceed gravity at centre unless the centre rotated at a faster angular velocity.
 
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If centrifugal force does not exceed gravity at surface, it will not exceed gravity at centre
In theory there actually is a case where it does: a rotating donut. But there isn't a cavity and it is not stable.
 
PAllen
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The link below doesn't address the cavity portion of your question, but it does address extremely rapid pulsar rotation and centrifugal force. I don't know if this theory could be reconciled with Janus' comment (his statement would seem to rule out a blitzar being possible), but here it is anyway...

https://en.wikipedia.org/wiki/Blitzar
I don't see anything in @Janus comment that is inconsistent with blitzar as a possibility. Can you explain your line of thougth?
 
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I don't see anything in @Janus comment that is inconsistent with blitzar as a possibility. Can you explain your line of thougth?
the material aligned along the axis of spin would not have any of that pressure mitigated by the spin and would only be pulled in towards the center by gravity.
I took Janus' remark to suggest that a potential blitzar would be vulnerable to pressure along the polar axis (axis of spin). This would seem to indicate that the centrifugal force couldn't really hold off the collapse into a black hole for any length of time, since material could fall into the poles. I could certainly be in error regarding my interpretation of his comment.

Another theoretical object that might interest the OP would be a ringularity, if one exists it would have a very interesting cavity in the middle.

https://en.wikipedia.org/wiki/Ring_singularity
 
PAllen
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I took Janus' remark to suggest that a potential blitzar would be vulnerable to pressure along the polar axis (axis of spin). This would seem to indicate that the centrifugal force couldn't really hold off the collapse into a black hole for any length of time, since material could fall into the poles. I could certainly be in error regarding my interpretation of his comment.

Another theoretical object that might interest the OP would be a ringularity, if one exists it would have a very interesting cavity in the middle.

https://en.wikipedia.org/wiki/Ring_singularity
Ok, I see, but I doubt I didn't take it quite so literally. The general observation can be made consistent with holding off BH formation for somewhat overmassive spinning neutron stars by noting that BH formation is a global phenomenon. The spinning equatorial portion is effectively reducing the amount of matter subject to catastrophic collapse, so what is left no longer meets the threshold, until the spin slows down.
 
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Good to know, I always hoped that a blitzar would someday be detected. It would be an excellent opportunity for study as it wound down into a black hole. :)
 

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