In article ,
(Eric Flesch) writes:
If dark matter resides throughout an elliptical galaxy or
globular cluster (or the Galactic halo) then it could raise the
ambient background gravitational level to where a resident star no
longer feels the gravitational effect from its neighbours or from
the system centre. Instead, the star would follow thre contours
(potentials) of the dark matter structure. So stars would just
mingle throughout without following orbits as such.

What distribution of dark matter are you postulating? If the
distribution is uniform, then the dark matter has no effect
regardless of how much of it there is. If the distribution is
spherically symmetric, then we have the familiar case where each
object responds to the amount of matter interior to that object's
position relative to the center of the dark matter distribution. If
the distribution is more complicated, then so are the effects, but in
any case, stars are affected in the usual way by other stars. I
suppose if you have clumps of dark matter (say tens or hundreds of
solar masses each) whizzing around randomly, the overall effects
could look random, but it's hard to see how such dark matter clumps
could form or be held together or why they should inhabit elliptical
but not spiral galaxies.

A nice calculator for galactic rotation curves is at
http://burro.astr.cwru.edu/JavaLab/R...eWeb/main.html
but it didn't work when I tried it just now. (I suspect some kind of
Java compatibility problem.)

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