The article shows two demonstrations: 1) a spiral galaxy and 2) a triple system (a neutron star and a white dwarf orbit each other, with another white dwarf orb

The article shows two demonstrations: 1) a spiral galaxy and 2) a triple system (a neutron star and a white dwarf orbit each other, with another white dwarf orbiting the pair at a distance). I think the spiral galaxy is showing that the problem is that it still has the arms attached. After this amount of time they should not be there so either the amount of time assumed is wrong or something is modifying the speed (like dark energy, modified Newtonian dynamics, etc). However, I don't understand what the "fall" in the triple system is about. What are they measuring that agrees with Newtonian Physics?