A black and white line plot of rotation curves for several galaxies, taken from the paper by Rubin, Ford, and Thonnard. In all cases the curves show unexpected behavior, with orbital velocities remaining roughly constant or even increasing out past the point where the luminous matter of the galaxy drops off.

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1. Robert McNees (mcnees@mastodon.social)'s status on Sunday, 23-Jul-2023 20:04:26 UTC Robert McNees

   in reply to

   Instead, Rubin et al measured rotation curves that became roughly *flat* out past the point where the density of luminous matter dropped off. And stuff at the edge of the galaxy was orbiting too fast given the matter they could account for.

   The 1980 Astrophysical Journal paper by Rubin, Ford, and Thonnard is usually cited in textbooks discussing this phenomenon. Look at those rotation curves!

   https://ui.adsabs.harvard.edu/abs/1980ApJ...238..471R/abstract

   Image: Astrophysical Journal, Vol. 238, p. 471-487 (1980)