On Tue, 04 Apr 2017, Steve Willner wrote:
(Eric Flesch) writes:
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

My point is that "dark matter" could be gravitationally opaque even as
it gravitates. We know it has different qualities than baryonic
matter, but we're not yet at the point where "we know what we don't
know". So it could act to muffle the gravitational environs of
ellipticals (etc) while responding to those environs in ways that
creates contours from it. Gravitational permeability & permittivity,
anyone? From outside the system its gravitational effect would be
indistinguishable from baryonic matter.

[[Mod. note -- The notion of "gravitationally opaque" doesn't exist
in general relativity, so if you want this then you need to come up
with a new theory of gravity.
-- jt]]