Quote:
Originally Posted by neilzero
Apparently spiral galaxies do not wind up tightly as would be expected if the speed of the outer stars was only twice the speed of the stars 5% of the way from the center. If the mass was mostly near the center we would expect the inner stars to be at least twice as fast, so there is a discrepency of at least 4 times, which it is explained as possible due to dark matter. I don't think so Tim. Perhaps the spiral galaxies started spiraling 137,000 years ago instead of 13,700,000,000 years ago. I don't know, but it does not compute. Neil
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From the diagram on Wiki Cougar linked to, and from other links I have seen, it looks to me like the constant speed, at least for the Milky Way, I believe, begins at about one-third of the radius, or about 5 kiloparsecs. Closer to the center, it looks like a roughly steady drop to zero, so half the speed should be observed at about half the distance to the point where it becomes constant, or at about one-sixth of the radius instead of 5%, shouldn't it?
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