Dark matter was needed to give the stars in a spiral galaxy a cause of their speed. So they proposed there must be some extra dark matter in the Galaxy. The total extra mass of dark mater is quite high. As a consequence of that, the whole galaxy becomes much heavier. But in the group or a cluster, the Galaxy also has a speed relative to other galaxies. So my question is whether the mass needed to give the stars their speed is the same mass that is needed to explain its movement within its cluster or a group?