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I thought that was actually true. Why are you calling it tired and old?
by cousin_it 12y ago
I thought that was actually true. Why are you calling it tired and old?
- phkahler 12y ago>> I thought that was actually true. Why are you calling it tired and old? Because there is no reason to expect stars going around a galaxy to follow keplers laws for two body systems. I have yet to see the measured rotation curves compared to an "expected" curve where the author doesn't use Kepler as part of the expectation. Just a year or two ago, I saw a paper in Nature where they were looking at a gas cloud forming a star, and they compared its rotation to something based on Kepler. I just had to shake my head - the correlation was there but not a great fit of course. The curve is interesting, the comparison not so much.
- blackhaz 12y agoWhy wouldn't they follow a Keplerian orbit?
- tim333 12y agoKepler's laws can be a pretty good approximation to reality and probably good enough for figuring if the galaxy contains unseen matter.
- rotorblade 12y ago> Because there is no reason to expect stars going around a galaxy to follow keplers laws for two body systems. The 'Kepler' law for galaxies are modified to accommodate for a mass distribution. See e.g.: https://en.wikipedia.org/wiki/Galaxy_rotation_curve#Halo_density_profiles https://en.wikipedia.org/wiki/Galaxy_rotation_curve#Halo_den...
- phkahler 12y agoNice article: This profile closely matches the expectations of a singular isothermal sphere profile where.... Why should the dark matter form a spherical blob? Right, because that's what makes Kepler behave better. But how the heck does the dark matter behave? Why should it take this distribution? It seems to be all made up to only explain observation, but not itself.