- This question refers to Wikipedia article on Milky Way, section on Galactic Rotation curves. I am referring to the graph on the right showing actual speed, in km/s, to distance from center of galaxy, in kpc. The actual speeds depend on the distribution of dark matter.
The graph in Wikipedia, article Milky Way, section Galactic Rotation, shows the actual rotation speeds in blue and the calculated speeds due to observed mass in red. (The graph is to the right of the article.) At about 3 kpc the actual speed is about 205 km/s. To account for the decrease in orbital speed around the center of the Milky Way, less centripetal force is needed, that is, less gravitational force. To account for this decrease in speed, dark matter needs to be located further out, lets say at 10 to 15 kpc. At 12 kpc, the orbital speed is about 220 km/s. To account for this increase in speed, a higher centripetal force is needed. To increase gravity at this distance, more dark matter closer to the galactic center is needed at lets say 3 to 7 kpc. But dark matter closer to the center will increase the orbital speed at 3 kpc. Is there a contradiction here? I know the Wikipedia articles in science and mathematics are correct and have been reviewed. Please explain.