“Motions of the stars tell you how much matter there is. They don’t care what form the matter is, they just tell you that it’s there.” -Pieter van Dokkum
Everything in the Universe was born with the same ratios of dark matter to normal matter: approximately 5-to-1. It shows up in everything from the cosmic microwave background to galaxy clustering to internal motions of spiral and elliptical galaxies, including the Milky Way.
But some galaxies, particularly dwarf galaxies and rapidly moving galaxies within clusters, show a significant enhancement of dark matter over what’s expected. Ratios of even hundreds-to-1 aren’t unheard of. This is a difficulty for theorists to explain, but it doesn’t mean that dark matter is wrong.