Thegrawity of the visiblemattcr in the Oalaxy is not enough to explain the high orbital speeds of stars in the Gdaxy. For escample, the Sun is moving ab out 60 km/sec too fest, Thepart of therotatfon curve contributed by thevisible marter only is thebottom curve. Thediscrepancy between thetwo curvesis evidencefor adarkmattar hab.