Modified Gravity works well for Gas Rich Galaxies

The motion of stars and gas in galaxies surprisingly is not so easily explained by the gravity they produce. They tend to follow flat rotation curves - after a certain distance the velocity tends to be the same whether a star is nearer or farther from the center of the galaxy. It had been expected that more distant stars and gas would be moving slower. The most popular explanation for this is dark matter , that 80% of the mass of galaxies like our Milky Way is some new unseen form that doesn't interact much, except by gravity. Another possible explanation is MOND, a theory that modifies gravity when it is very weak. A recent preprint shows that MOND works very well for gas-rich galaxies while dark matter is rather less natural and convincing: A Novel Test of the Modified Newtonian Dynamics with Gas Rich Galaxies.