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Moving galaxy

  1. Apr 21, 2003 #1
    I had come across some scientific articles that Galaxy is actually moving across the space!

    Is that movement due to initial explosion of the universe? The big-bang?

    When thing moves, it has energy 1/2M.V^2 ,
    if the galaxy which is so huge is moving, from where does it get the kinetic energy ?[?]
  2. jcsd
  3. Apr 22, 2003 #2
    Well, there's the expansion of the universe, and there's the peculiar motion due to gravitational interaction with nearby galaxies.
  4. Apr 23, 2003 #3
    Then where the Universe expands? To another Universe ???
  5. Apr 23, 2003 #4
    Well, we don't really know, but the physics and the mathematical models behind it don't require another universe into which our universe is expanding.
  6. Apr 23, 2003 #5
    this is where having no center point to the univerce [x=0 y=0 z=0] is a problem, what do we reference galatic movement to???
    secondary questions we spin , but does the milkyway tumble,wobble, or have a proper motion other than a orbit in the local group + expansion, does the local group have proper motion other than expansion???
  7. Apr 24, 2003 #6
    You can reference it to the cosmic expansion itself (i.e. the Hubble flow). One can use the cosmic microwave background radiation (CMBR)for this purpose. If we were at rest with respect to the Hubble flow, then the CMBR would look isotropic on the large scale (after subtracting out the telescope's motion around the Sun, and the Sun's orbit around the Milky Way). But it doesn't. Subtracting out the motion of the Milky Way and our Local Group makes the CMBR isotropic. There are other methods, too.
  8. Apr 24, 2003 #7


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    Do you happen to know the speed and direction of our galaxy's motion with respect to the Hubble flow? It seems to me that it would be cool to know that and be able to point at it some night when it was up and say that's where our galaxy is heading, and to know the speed the Milkyway G is traveling as well.
  9. Apr 24, 2003 #8
    I believe the peculiar motion of our galaxy is due to a number of things. Firstly there's the motion of our galaxy within the Local Group, then there's the motion of our Local Group towards the centre of the Virgo supercluster (of which the Local Group is an outlying member), and then there's the motion of the Virgo supercluster towards the so-called "Great Attractor", a region of mass a million times more massive than our galaxy. This last motion towards the "Great Attractor" is directed at the vicinity of the constellations of Hydra and Centaurus at a speed of roughly 600km/s.

    It would be an interesting literature search project to find the speed due to:

    1) The rotation of the Earth
    2) The orbit of the Earth around the Sun
    3) The motion of the Sun through it's local neighbourhood
    4) The rotation of the Milky Way Galaxy
    5) The motion of the Milky Way Galaxy through the Local Group
    6) The motion of the Local Group towards the Virgo Supercluster
    7) The motion of the Virgo Supercluster towards the Great Attractor
  10. Apr 25, 2003 #9


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    This is the right time of year to be thinking about the directions to Virgo and Hydra and Centaurus. They are on or close to the meridian around 10PM. Leo is just a little west of the point overhead. Hydra and Centaurus are pretty far south, so close to the horizon, but Leo and Virgo are readily visible. Good time to get these motions in various directions visually sorted out.

    This is for May 1 at 10PM, plus or minus two weeks --> minus or plus one hour. At 30 N latitude the milky way ring coincides with the horizon then, more or less.

    I guess that items 3 through 7 on your list add up to the solar system heading for Leo at roughly a thousandth of the speed of light. Items 1 and 2, the earth's rotation and revolution, have a comparatively small---ten percentish---effect on that. So when imagining those velocity vectors 3-7, one should picture them adding up to a vector that points at the constellation Leo. Or?
  11. Apr 25, 2003 #10
    I don't know, marcus. That would be an interesting thing to find out.
  12. Apr 25, 2003 #11


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    I'm tempted to claim that this picture proves it:


    It shows the CMB against a field of stars and the hotspot is squarely on Leo

    I think items 3 thru 7 of your list have to add up to
    the absolute motion of solar system relative to CMB
    and we know that is direction Leo

    (unless a diabolical creator put an intrinsic dipole anisotropy
    into the CMB just to throw us off, a mischievous dipole unrelated
    to our motion)

    Geometrically this list just has to add up to the sun's net motion relative CMB, can't picture it any other way. Flaw in my reasoning?
  13. Apr 26, 2003 #12
    Only that the list may be incomplete. Perhaps the Great Attractor is being attracted to an even Greater Attractor?
  14. Apr 26, 2003 #13


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    should have thought of that

    having CMB restframe sure simplifies one's perspective
    because one just says solar system
    (as a result of all its motions combined)
    is heading in direction of Leo

    its when one tries to *parse* the motion
    that it gets hairy

    I wrote to Peat of Heavens-above to suggest
    that he post a map like that U2 one with
    the hotspot superimposed upon a field of stars
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