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The Sun is very spherical - allegedly

  1. Aug 23, 2012 #1

    sophiecentaur

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    I read this Scientific American link and I found it very interesting.
    I have a problem understanding it, though, because I had read that one of the explanations for the existence of Solar Systems is based on Angular Momentum. The argument goes that if all the mass were concentrated in the host star, the rotation rate would be such that material would be shed from it and so the planets have a significant share of the total angular momentum of the system. That would suggest to me that you'd expect the Sun to be Oblate - like many / most planets - rather than the near perfect sphere they seem to have found.

    Was that theory commonly held until this recent measurement?

    [Edit - or is there still some odd distribution of mass within the Sun?]
     
  2. jcsd
  3. Aug 23, 2012 #2
    Is that theory saying planets formed from the ejecta of proto-stars? Or is it saying that IF all the material went into the star it would likely spin much of it off again?

    I am unfamiliar with the former. If the latter case, I can see why it might not hold after this observation but it depends on what is maintaining sphericity. The strength of magnetic, nuclear, and gravitational forces seem to be dominating angular momentum at this rotational speed, at least.

    I mean, the mass distribution IS odd, in that it isn't as oblate as one would think... I may have misunderstood your post.
     
  4. Aug 24, 2012 #3

    sophiecentaur

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    Thanks for the reply. You seem to be agreeing that there must be something odd - which is reassuring for me!
    I'm being a bit vague about this because it's a vague memory (anno domini, you know) and I'm not sure which of those theories applied to the argument. I think the logic would assume that all the material was part of the same entity, initially.

    I suppose that it must be some magnetic effect because the nuclear forces are pretty local. When you think that Jupiter is 'almost big enough' to be a star and it is noticeably oblate, you'd expect stars to be oblate too. Perhaps someone else will contribute and put us wise.
     
  5. Aug 24, 2012 #4

    Drakkith

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    I think I remember reading that the Sun shed angular momentum early in it's life through the interaction of it's magnetic field with the solar wind or something.
     
  6. Aug 24, 2012 #5

    sophiecentaur

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    The plot thickens!! But the Sun does rotate somewhat because I'm sure the sunspots move about. Perhaps that's only the outer layer?? But what about the drag?
     
  7. Aug 24, 2012 #6

    Drakkith

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    Of course the Sun rotates. What drag are you referring to?
     
  8. Aug 24, 2012 #7

    sophiecentaur

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    You wrote that it shed angular momentum - but you didn't imply all of it. So why would it stop doing that, I wonder?
     
  9. Aug 24, 2012 #8

    Drakkith

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    Perhaps the rate of loss slowed as it's rotation slowed?
     
  10. Aug 24, 2012 #9

    sophiecentaur

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    That could make good sense.
     
  11. Aug 24, 2012 #10
    I can think of one additional processes that might reduce angular momentum of the sun.

    Planets that experience tidal effects from the Sun's gravitation slowly increase their period of orbit, i.e. get further away. At a further distance they take up more of the systems total angular momentum, thus the Sun slows its spin.

    Also, large planets like jupiter and saturn may have pulled in sizeable amounts of material that was previously in a closer orbit to the sun. This would also absorb angular momentum from the system.
     
  12. Aug 24, 2012 #11

    Dotini

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    SDO is bringing to light some interesting anomalies well worth questioning.

    They also found that the solar flattening is remarkably constant over time and too small to agree with that predicted from its surface rotation. This suggests that other subsurface forces, like solar magnetism or turbulence, may be a more powerful influence than expected.
    http://www.sciencedaily.com/releases/2012/08/120816150801.htm

    Respectfully submitted,
    Steve
     
  13. Aug 24, 2012 #12
    Actually, I wonder about this. The surface rotates, but do we have any direct observations of the rate of rotation of the core? Or is it just all inferred?
     
  14. Aug 24, 2012 #13

    Drakkith

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    No idea. I would expect the core to rotate given that the rest of the Sun does, but I really have no clue.
     
  15. Aug 24, 2012 #14

    davenn

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    from Wiki.....
    that I didnt know till now ;)

    Dave
     
  16. Aug 24, 2012 #15
    A priori it would be nigh impossible for a great cloud of material to fall in on itself and have a net zero angular momentum.
     
  17. Aug 25, 2012 #16

    sophiecentaur

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    So where does this all take us in the "why is it so damned spherical?" question? Would all stars be the same, do you suppose?
     
  18. Aug 25, 2012 #17

    Drakkith

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    Nope. Vega is spinning VERY fast. It spins at 87.6% the speed that would tear it apart.

    http://en.wikipedia.org/wiki/Vega#Rotation
     
  19. Aug 25, 2012 #18

    sophiecentaur

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    How spherical is Vega? Has the spin affected its shape? Does it have much mass around it in the form of a solar system (which could have pinched some of its angular momentum)?
     
  20. Aug 25, 2012 #19
    Vega is also a very young star, still surrounded by its proto-stellar cloud of dust and gas. It could be stars have initially high spin which slows over time through interaction with their own nebular disk.

    For our Sun, it implies that there is still quite a bit more to learn about whats really going on inside :)
     
  21. Aug 25, 2012 #20

    Chronos

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