John Baez wrote in message
...

In article ,
Norm Dresner wrote:

Since it's believed that there's a dark matter "halo" around or
containing
every normal matter galaxy, [...]

Just to throw an interesting spanner in the works, the April 11th
issue of Science reports that Aaron Romanowsky at the University of
Nottingham claims to have found some galaxies *without* dark matter
halos.

Other astronomers are skeptical, so we should wait to see whether
this gets confirmed or refuted. But if it were true, it would probably
be a big deal. For one, it would probably kill all MOND-like theories
in which dark matter is just an artifact of not understanding gravity
well enough. For two, folks would have a lot of fun trying to explain
such a thing could happen.



It is suggested that it was stripped away through interaction with other
galaxies. One characteristic of ellipticals is that they often do not have
concentrated mass cores. Does anyone know if this is true for these?

Another thing I am curious about is whether the motion of these galaxies
with respect to others also indicates that they are not surrounded by dark
matter. It seems to me that if it turns out that galaxies without
concentrated cores do not contain dark matter within their visible limits
but seem to still be surrounded by it could indicate a problem with our
understanding of the gravitational dynamics around massive cores. I gather
that some people think the dark matter problem could be associated with
black holes and that would be ruled out. And explaining it with dark matter
would at least get more complicated.

-Ed Keane III