[Moonman62]

These galaxies differed in both size and rotational velocity by up to a factor of 30. With these velocity measurements, the researchers were able to calculate the rotational period of their sample galaxies, which led them to conclude that the outer rims of all disk galaxies take roughly a billion years to complete one rotation.

...

The key to this study is they are only looking at the outer rims. FReepers who only read the headlines won’t know this.

[LibWhacker]

But remember, Vera Rubin showed the outer rim of a galaxy rotates just as fast as the stars interior to it. Everything's rotating like a giant phonograph record. See my comment #8 above. The only explanation is dark matter, or so they say. I believe they.