Yousuf Khan wrote:
A couple of years ago, it was found that there were some streamers of
gas that were flowing between Andromeda and Triangulum, which
scientists thought were the result of a possible near collision
between them.
Neighbor galaxies may have brushed closely, astronomers find
http://www.sciencedaily.com/releases...0611193632.htm

But now, after some further analysis, they are finding that there may
be something more significant here. They think the gas between the
galaxies are as massive as dwarf galaxies, but just more diffuse, so
there are no stars that formed in them. So the nearly invisible gas
is likely to be independent from either galaxy. What's more, they
think that this gas came from an even bigger clutch of gas that has
so far remained invisible.
Astronomers discover surprising clutch of hydrogen clouds lurking
among our galactic neighbors
http://www.sciencedaily.com/releases...0508131700.htm

If this is true, then it's making it more and more unnecessary to look
for exotic WIMPs and other such things to explain dark matter, as dark
matter may simply be this invisible gas between galaxies.

This hypothesis does nothing to address the problem of dark matter being
present in galaxies. The rotation curves of spiral galaxies, for example,
was one of the first clues that dark matter exists and does not interact
with other matter except through gravitation. Another clue is in the
gravitational lensing of distant galaxies caused by massive elliptical
galaxies in clusters. There is far more lensing effect than can be
accounted for in the stellar populations, and ellipticals have very little
interstellar hydrogen.

--
Mike Dworetsky

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