To answer the qustion in the subject line, "for spiral galaxy disks,
yes, but not as a rigid body." Except near the galactic center, the
stars rotate with roughly constant _linear_ speed, meaning the
"galactic year" increases linearly with radius.
One resource I've recommended before is at
http://burro.astr.cwru.edu/JavaLab/RotcurveWeb/main_BACK.html
Elliptical galaxies I'm not sure about. For a long time, there was
no clear evidence of any overall rotation, but that may have changed
in the last few years.
In article <
be53f1de-518c-4cd1...@googlegroups.com>,
jonas.t...@gmail.com writes:
> If so it measurable over 10 k years, 100 k years or million of years?
The Sun's motion with respect to the radio source Sgr A* at the
Galactic center has been measured using Very Long Baseline
Interferometry. I'd have to look up the exact time time baseline,
but it would have been a few years. It's probably well over a decade
by now, giving much better precision than the original measurement.
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Steve Willner Phone
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