I’m busy trying to make filaments in the lab, but I just want to say that others have been doing more work on this observationally and the outer velocity curves of spirals, which are based on radio observations that measure the velocity of plasma, not stars, can be explained by the magnetic fields that are observed. At some point I’ll post the relevant papers. The one place where magnetic fields do not seem adequate for confining the mass of hot plasma observed is in clusters of galaxies. Some presently-unseen matter seems needed at the moment. However, that could be dim old stars in very old galaxies or even between galaxies that are too dim to be observed. This is more likely than exotic dark matter.
