Why do the outer fringes of galaxies spin at the same speed as the inner core? They shouldn’t. A galaxy should rotate faster at the center, where the stars are denser (and there’s usually a black hole).
In our solar system, the planets farther from the sun orbit more slowly, because gravity is weaker there. But this isn’t true of any galaxy whose rotational speeds have been measured.
Gravity comes from mass, so most scientists believe there’s matter we can’t see. They call it “dark matter.” Measurements suggest it comprises 85% of the matter in the universe.
It’s not known for sure that dark matter exists, but its imputed presence explains lots of things that otherwise are inexplicable. Read article here.
Photo: I don’t have a photo of dark matter, so I used this picture of a black cat in a coal mine to show it looks like.
Is it a Johnny Cash coal mine? Is it the Chesire Cat?
Is there a galactic turntable turning slate records?