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A random thought

  1. Sep 7, 2003 #1
    I was just wondering about something, and maybe someone can clue me in. I was thinking about how the Large Magellanic Cloud and Small Magellanic Cloud orbit our own galaxy. And I was thinking... I wonder if there are tidal forces at work? I mean, the same way that the Moon causes high tides and low tides on the earth. When a small galaxy orbits our own, does it slightly stretch out our galaxy, like a high tide?
  2. jcsd
  3. Sep 7, 2003 #2


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    it is a reasonable idea and the analogy is on the right scale I think

    the moon is 1/80 the mass of the earth
    I am not sure exactly what fraction LMC is of MW but I think
    it is about 1/100

    distance of LMC is about 50 kpc
    radius of MW is about 15 kpc
    please someone correct these figures if they are way off
    I am only sketching a rough idea

    I am thinking that the analogy is very good in that the LMC deforms the gravitational field quite a bit
    only it is not noticeable because in MW things revolve so slowly,
    sun takes over 200 million years to go around
    compared to our lifespan things are just standing still

    where by contrast
    the earth rotates fast enough for us to see the tidal effect.
  4. Sep 8, 2003 #3


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    Welcome to Physics Forums, Smiley! :smile:
  5. Sep 9, 2003 #4
    More likely our Galaxy exerts tidal forces on the Magellanic Clouds. Also, I seem to remember they found another satellite galaxy on the opposite side of the galactic plane to us. It was found as it has material streaming into the MW. We are canabilising the satellite through tidal forces.
  6. Sep 27, 2003 #5


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    Tidal forces? You bet!

    The Toomre brothers did some of the first modelling of galaxy interactions, several decades ago now. They showed that tidal forces pulled long tails and streamers of stars and gas out of galaxies which pass near one another. At that time the most spectacular pair had the name The Antennae; the Toomre's model reproduced the wonderful streamers very well.

    More recently, the newly installed ACS instrument in the Hubble Space Telescope took a wonderful picture of another tidal tail from an interacting galaxy pair. The HST collection also has a close-up of Stephan's Quintet.

    The Saggitarius Dwarf, which thed refers to, has just been in the news. Observations have shown that it is truly being torn to pieces by the Milky Way, through tidal interaction.

    Lastly, but not so widely reported, is a study showing a globular cluster being shredded by close encounters of the Milky Way kind. See this link:
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