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We all know that Milky Way exhibits Galaxy Rotation Curve which makes it rotate very differently that Newtonian mechanics would expect. But Milky Way is a pretty large galaxy, and the one we only see inside, so maybe it's not that good of an research object.

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What are the smallest galaxies or star clusters whose rotation is clearly non-Newtonian? Are dwarf galaxies' rotation curves affected? Are globular clusters inside galaxies such as ours affected, or is their movement decisively Newtonian?

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  • $\begingroup$ Which theorized explanation are you going with? (dark matter, MOND, etc.) Why do you expect the effect to go to zero for anything at all, i.e. perhaps it affects planets but by an immeasurably small amount. $\endgroup$
    – Carl Witthoft
    Dec 13, 2019 at 15:01
  • $\begingroup$ @CarlWitthoft I don't go with any, I'm just asking which ones are in need of any explanation? I don't expect effect go to zero but I expect that it stops being observable eventually. $\endgroup$
    – alamar
    Dec 13, 2019 at 15:54

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Yes, dwarf galaxy rotation curves are affected -- in fact, they tend to require relatively more dark matter than is required to explain the rotation curves of giant galaxies like the Milky Way. The smallest known systems are so-called ultrafaint dwarf galaxies (UFDs), which can have as little as $\sim 10^{4}$ solar masses worth of baryons (in the form of stars), but apparently have as much as 100 times this in the form of dark matter -- versus the roughly 10:1 (DM:baryons) case for galaxies like the Milky Way. This means that some of these systems have fewer stars than typical globular clusters.

But globular clusters, on the other hand, do not show signs of dark matter/non-Newtonian motion: you can explain the motions of their stars as being due to the normal, Newtonian gravity of all the baryonic mass (i.e., the stars, plus a plausible amount of stellar remnants like neutron stars and stellar-mass black holes).

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