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mhajicek [soylentnews.org] writes:

According to this paper, the calculations of spiral galaxy spin which required the dark matter fudge factor were oversimplified. If you actually model the spiral arms in detail the results match observations without the need for dark matter:

https://arxiv.org/ftp/arxiv/papers/0903/0903.1962.pdf [arxiv.org]

"Abstract The gravity fields and rotation curves of whirlpool galaxies with thin disc distribution of material
are calculated numerically. It is proved that the gravity field of mass thin disc distribution is greatly
different from that of spherically symmetrical distribution. As long as the Newtonian theory of gravity is
used strictly, by the proper mass distributions of thin discs, the flat rotation curves of whirlpool galaxies can
be explained well. The rotating curve of the Milky Galaxy is obtained which coincides with practical
observation. In this way, it is unnecessary for us to suppose the existence of additional dark material in the
illuminant discs of whirlpool galaxy again. Meanwhile, in the space outside the illuminant disc, the
quantity of dark material needed to maintain the flatness of rotation curves is greatly decreased. By
considering the observation fact that the quantity of non-luminous baryon material is 3~10 times more than
luminous material, we can explain the flatness of rotation curves of whirlpool galaxies well without the
hypotheses of non-baryon dark material. So it is unnecessary for us to suppose that non-baryon dark
material is about 5 times more than baryon material in a single whirlpool galaxy, no mater whether
non-baryon dark material exits or not."

Original Submission