I have read some information, from various sources, pertaining to the orbital speed of stars about the center of galaxies, and some of it appears to be conflicting. Some sources claim that the stars closer to the galactic center orbit faster, while those father out, orbit slower. This of course seems to follow traditional laws of gravitation. However, I have also read that it has been documented that all the stars in galaxies seem to orbit the center at the same speed, regardless of their distance from the center. This so baffled scientists, that it was one of the reasons for postulating the existence of so-called "dark matter" to account for "missing mass". So, my question is, does anyone have any definitive answer to which is correct?