Shapes and gravitational radiation

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Discussion Overview

The discussion revolves around the detectability of gravitational radiation emitted by different shapes of mass distributions, particularly focusing on the differences between perfect spheres and ovoid shapes. It touches on theoretical aspects of gravitational radiation and the conditions under which it can be produced.

Discussion Character

  • Technical explanation, Conceptual clarification, Debate/contested

Main Points Raised

  • Some participants propose that a perfect sphere will not be detectable by gravitational detectors, while an ovoid shape will be detectable, questioning the reasons behind this distinction.
  • One participant references a Wikipedia article stating that gravitational radiation is emitted only when there is spherically asymmetric motion among masses, using spinning neutron stars as an example of objects that typically do not emit gravitational radiation due to their near-perfect spherical shape.
  • Another participant mentions that slight surface deformities on neutron stars, referred to as "mountains," can create a changing quadrupole moment, which may lead to the emission of gravitational waves.
  • Some participants express confusion regarding the mechanism for the production of gravitational radiation and the necessity of a changing quadrupole moment for its generation.

Areas of Agreement / Disagreement

Participants appear to have differing levels of understanding regarding the mechanisms of gravitational radiation, with some agreeing on the necessity of asymmetry for emission while others express confusion about the underlying principles. The discussion remains unresolved regarding the clarity of these mechanisms.

Contextual Notes

There are limitations in the discussion regarding the assumptions made about mass distributions and the specific conditions required for gravitational radiation, as well as the definitions of terms like "quadrupole moment." These aspects are not fully explored or clarified.

wolram
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IIRC , a perfect sphere will not be detectable with a gravitational detector, but an ovoid shaped body will, why is this so? or am i wrong.
 
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wolram said:
IIRC , a perfect sphere will not be detectable with a gravitational detector, but an ovoid shaped body will, why is this so? or am i wrong.
Why do you think what you think?
 
I found this on wiki
Vhttps://en.wikipedia.org/wiki/Gravitational_wave#Rotating_neutron_stars

As noted above, a mass distribution will emit gravitational radiation only when there is spherically asymmetric motion among the masses. A spinning neutron star will generally emit no gravitational radiation because neutron stars are highly dense objects with a strong gravitational field that keeps them almost perfectly spherical. In some cases, however, there might be slight deformities on the surface called "mountains", which are bumps extending no more than 10 centimeters (4 inches) above the surface,[45] that make the spinning spherically asymmetric. This gives the star a quadrupole moment that changes with time, and it will emit gravitational waves until the deformities are smoothed out.
 
So it seems you have answered your own question.
 
phinds said:
So it seems you have answered your own question.

No, I do not understand the mechanism for the production of gravitational radiation.
 
Last edited by a moderator:
In order to have gravitational radiation, you have to have a changing quadrupole moment of the field. A simple spinning sphere won't have that.
 
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