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B Spiral Galaxies' Arms

  1. Dec 19, 2016 #1

    Sanborn Chase

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    Why do the arms of spiral galaxies usually bifurcate? Is the visible matter in them moving in or out from the center?
     
  2. jcsd
  3. Dec 19, 2016 #2

    Drakkith

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    The visible matter is mostly moving in complicated elliptical orbits about the center of the galaxy, but I'm sure a small amount is sent towards or away from the center due to gravitational interactions. I can't answer why they are bifurcated though.
     
  4. Dec 19, 2016 #3

    davenn

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    2 armed galaxies are only one of many forms, many have multiple arms, many have none that can be easily identified
     
  5. Dec 19, 2016 #4
    One thing to keep in mind is that spiral arms in galaxies are "density waves" and not actual structures of the matter. They represent the area where many millions of stellar orbits reach their maximum distance from the galactic center of mass. At this point they are traveling the slowest and so "pile up" in the region producing the appearance of more stars than in-between the arms. But the individual stars in each arm are changing continuously.

    Put another way, the arms are an illusion. They aren't like a whirlpool or anything like that.
     
  6. Dec 20, 2016 #5

    davenn

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    ohh yeah ???
    I would like to see some valid citations for your comment !!

    there is NO "appearance" they are really there you can see them go supernova, you can do spectroscopic work on those stars

    Their location IS physical

    Dave
     
  7. Dec 20, 2016 #6

    Sanborn Chase

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  8. Dec 20, 2016 #7
    The stars are real but the arms in a spiral galaxy are not; as I stated, they are simply an illusion. I'd recommend An Introduction to Modern Astrophysics as a reference. It's in one of the later chapters if I recall correctly...

    (Think of where an oscillating particle spends most of its time: on the edges of its motion. This is because it is traveling slowest at that point. It's the same thing with galaxies and stellar orbits. The stars just spend more time there.)
     
  9. Dec 21, 2016 #8

    Chronos

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    The stars in a galaxy really are [were, given the finite speed of light] where they appear to be as Dave noted, however, Rex is correct in that they do not form and remain in spiral arms as they orbit a spiral galaxy. Their individual motions follow a density wave profile as illustrated here .
     
  10. Dec 21, 2016 #9

    Sanborn Chase

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    First, thank you all for taking the time to answer my questions.
    Chronos, the video clip of the motions of stars in a spiral galaxy was most illuminating and answered the second part of my first post concerning the movement of individual stars into and out of the center.
    As the galaxy itself is moving through space(and time) would it not form the basic configuration of a transformer?
    Again, many thanks to all of you.
     
  11. Dec 21, 2016 #10
    Excellent video!

    Sanborn Chase, do you mean an electric transformer?
     
  12. Dec 21, 2016 #11

    Sanborn Chase

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    Yes, an electrical type transformer in its form. And Mr. Bernhardt cautioned me about posting pet theories, personal opinions, etc. I trust I haven't bent the pipe.
     
  13. Dec 21, 2016 #12

    Drakkith

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    No. Not at all.
     
  14. Dec 21, 2016 #13

    phinds

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    I'm curious what characteristic led you to that conclusion. I must be missing something because I just don't see it at all. I mean, I know that it's NOT, I'm just curious why you think it might be.
     
  15. Dec 21, 2016 #14
    Probably because of near or actual collision with other galaxies,
    More galaxies are spheriod/elipitical
     
  16. Dec 21, 2016 #15

    Sanborn Chase

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    I may have been misunderstood by Mr. Phinds; spiral galaxies when considered over time seem to describe a form similar to an electrical transformer. I don't believe they are electrical transformers, although they may be. I'm trying to understand the reasons for the various forms galaxies take on as they transform one or more things into others. Their forms must follow their purposes.
     
  17. Dec 21, 2016 #16
    A galaxy has a purpose?
     
  18. Dec 21, 2016 #17

    berkeman

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    Say which what?
     
  19. Dec 22, 2016 #18

    Sanborn Chase

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    Have I said something heretical? Is it not proper to assume the stars have arranged themselves so for a reason, and this may be worthy of our scrutiny?
     
  20. Dec 22, 2016 #19
    I think we're all confused why a galaxy seems related to an electrical transformer. Perhaps you could explain what you mean?

    The motion and arrangement of stars in galaxies is deeply studied. It's really quite interesting!
     
  21. Dec 22, 2016 #20

    phinds

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    No, the stars do not "arrange themselves". That puts an anthropomorphic spin on inanimate objects and thus is not science. Studying how the stars are arranged is certainly a valid (and interesting) field of study but let's not bring consciousness into it.
     
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