In this article, G increases with a decrease in radius requiring that the velocity of stars increase substantially. I would be curious if this could accurately model dark matter?
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Odds are that G is a constant. Period. However, measuring G, even on the Earth, is very difficult, so its constancy has not been experimentally proven; and no tests of its value can presently be conducted anywhere else. So although it would destroy some of the most useful concepts in physics -- that constants are constant, and the Universe works in the same way everywhere -- it is possible that G varies in some unknown way.
However, odds are that dark matter is just stuff that's hard to observe, as discussed in my webpage, Dark Matter In Galaxies (see https://cseligman.com/text/galaxies/dark.htm ). The trouble is that no matter what "dark matter" is will probably not be proven within our lifetimes, so even if right your paper will be forgotten long before the actual answer is found. And proving that your paper is correct is unlikely to be possible within the entire lifetime of the human race, as it would require measurements in places that we will never reach.