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Galactic mass proportional to r

  1. Dec 8, 2003 #1
    How do I calculate galactic mass as a function of r? I know it is supposed to be proportional to r. I've seen,
    And also I've seen
    Which if any is right?
    And what do I use for v?
    Thanks so much for your help!
  2. jcsd
  3. Dec 8, 2003 #2
    The rotation curve is flat so I can find v by plugging in the radius and total mass of the galaxy. Doing that I get,
    M(r)=Mr/R, where M is the total mass of the galaxy and R is the radius of the galaxy
    I'm trying to do a tidal force calculation to see how far away from the center of a galaxy a star needs to be to be tidally disrupted by a nearby galaxy. I'm getting
    r=(d3m/(2MR))1/2 where m is the total mass of the galaxy that the star lies in, R is the radius of that galaxy, M is the total mass of the nearby galaxy, and d is the distance between the two galactic centers. Can anyone verify this?
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