Re:All disk galaxies rotate once every billion years: study
by samschooler on Wednesday March 14, 2018 @12:53PM
(#16586165)
I’d actually love to get an explanation for this. Do galaxies work similar to solar systems in that all objects are in orbit around a central mass or is it a different phenomenon that binds matter together into a galaxy?
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Re:All disk galaxies rotate once every billion years: study
by mutagen on Wednesday March 14, 2018 @02:22PM
(#16587053)
The mass of the central black hole is a tiny fraction of the mass of the galaxy, it might be more correct to say that the objects in a galaxy orbit the common mass (including dark matter) of the galaxy.
For example, the black hole at the center of the Milky way is estimated at 4.1×10^6 M (solar mass) and the total Milky Way mass is estimated at 0.8–1.5×10^12 M (figures from Wikipedia).
Some interesting articles found while digging for these numbers:
https://ned.ipac.caltech.edu/level5/Merritt/Merritt1.html
Re:All disk galaxies rotate once every billion years: study
by kwoff on Wednesday March 14, 2018 @02:12PM
(#16586955)
Planets orbit around the center of mass. It's coincidental that the center of mass is (at least in our case) at the sun's location, because the sun has most of the mass.