Neutron Star Core: Empty Obloid Cavity & Exotic Content?

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Discussion Overview

The discussion revolves around the structure and properties of neutron star cores, particularly the possibility of an empty obloid-shaped cavity forming due to centrifugal forces in rapidly spinning neutron stars. Participants explore the implications of such a cavity, including what it might contain and the effects of relativistic phenomena.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • One participant questions whether centrifugal force could displace core material outward, potentially creating an empty cavity in the center of a millisecond spinning neutron star.
  • Another participant argues that while gravity decreases toward the center, pressure from the weight of the material above increases, suggesting that material aligned along the spin axis would still be pulled inward by gravity.
  • A hypothesis is presented that the neutron core could consist of quark matter, referencing strange quark stars as a related concept.
  • Some participants discuss the dynamics of centrifugal force and gravity, noting that if centrifugal force does not exceed gravity at the surface, it will not do so at the center, implying stability against cavity formation.
  • There is mention of a theoretical object known as a ringularity, which could have a cavity and might be of interest in this context.
  • Concerns are raised about the stability of a potential blitzar and its vulnerability to collapse due to pressure along the polar axis.

Areas of Agreement / Disagreement

Participants express differing views on the formation of a cavity in neutron star cores, with some arguing against it based on gravitational and centrifugal dynamics, while others propose alternative models involving exotic matter or theoretical constructs. The discussion remains unresolved with multiple competing views present.

Contextual Notes

Participants note the complexity of the forces at play, including the interplay between centrifugal force and gravitational pressure, as well as the implications of relativistic effects and exotic matter in the context of neutron stars.

Srb2001
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TL;DR
Do millisecond Neutron Stars cavitate in their cores?
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
 
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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.
 
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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.
 
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
 
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.
 
snorkack said:
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.
 
Rubidium_71 said:
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?
 
PAllen said:
I don't see anything in @Janus comment that is inconsistent with blitzar as a possibility. Can you explain your line of thougth?
Janus said:
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
 
Rubidium_71 said:
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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