> [!tldr] Stars at the edges of galaxies are moving too fast This is one of those questions that always bothered me - why do we think there's this stuff called "Dark Matter" that we can't detect that makes up supposedly 90+% of the universe? Turns out at least one of the bigger reasons is that stars at the peripheries of galaxies are being held in place by more centrifugal force than we think they should. They are too big and moving too fast to not just "fly away" from their system. > Like a weight on a string, if the string is short, the weight flies around quickly. If it's long, it can take its time. So we balance the pull of what we can see with the math by basically adding in a "dark matter" terms. The whole area makes me feel dumb. **** # More ## Source - [[13 Things That Don't Make Sense]]