I think they need to rewrite that paper. It's so filled with qualifying clauses, I can't tell what they are trying to say.SpaceTiger said:Galaxy collisions and dense clusters are, theoretically, an excellent testing ground for dark matter theories. Since the baryons are coupled to one another by non-gravitational forces, they may become separated from the dark matter, which can only interact gravitationally. If this happens, then we can use gravitational lensing to to compare the mass peaks to the light peaks. This is exactly what was done in Clowe et al. 2003 (linked earlier in the thread).
Unfortunately, there are very few systems in which this kind of analysis can be done, so I wouldn't say that they have yielded definitive proof. However, results are so far consistent with particle dark matter theories.
Are they saying that one would expect the mass centroid to be coincident with the light centroid, but they find through lensing effects that the mass centroid in not coincident with the light centroid due to the invisible dark matter contribution? What paragraph did they say that exactly.