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It has occurred to me from the statements in various threads that I may be misunderstanding the effects of dark matter, so I'd like someone to either verify that I DO in fact have it right, or that I am mistaken.
MY understanding is that dark matter:
(1) has a gravitational effect on galaxies and causes the stars out from the center to rotate around the galactic center faster than they would otherwise do and that this effect becomes more pronounced the further from the center you get, such that while the otherwise expected speed of rotation trails off with a slope as you move away from the center, the actual measurements (attributed to the effects of dark matter) show that the speed is pretty much uniform all the way out
(2) dark matter is clumped up in an apparently uniform distribution from galactic centers out to somewhere beyond outer edges of each galaxy but does not extend out forever into the space between galaxies. That is, it is uniform in and near a galaxy, but clumped when looked at on much larger scales.
(3) dark matter is NOT what holds galaxies together. They would stay gravitationally bound without dark matter but the outer stars would rotate more slowly if the dark matter were not there.
#3 in particular seems to contradict some statements I have read here (I may have just misinterpreted the statements) so that's the one I'm wondering about the most but I want to make sure I have all of them right, or that I GET it them right eventually.
Thanks
MY understanding is that dark matter:
(1) has a gravitational effect on galaxies and causes the stars out from the center to rotate around the galactic center faster than they would otherwise do and that this effect becomes more pronounced the further from the center you get, such that while the otherwise expected speed of rotation trails off with a slope as you move away from the center, the actual measurements (attributed to the effects of dark matter) show that the speed is pretty much uniform all the way out
(2) dark matter is clumped up in an apparently uniform distribution from galactic centers out to somewhere beyond outer edges of each galaxy but does not extend out forever into the space between galaxies. That is, it is uniform in and near a galaxy, but clumped when looked at on much larger scales.
(3) dark matter is NOT what holds galaxies together. They would stay gravitationally bound without dark matter but the outer stars would rotate more slowly if the dark matter were not there.
#3 in particular seems to contradict some statements I have read here (I may have just misinterpreted the statements) so that's the one I'm wondering about the most but I want to make sure I have all of them right, or that I GET it them right eventually.
Thanks