Understanding “dynamical friction”
“Dynamical friction” is a phenomenon first theorised by Chandrasekhar in the 1930's. It is a gravitational drag force that is likely responsible for galaxy-galaxy mergers, star cluster mergers, and even the merger of binary “super-massive” black holes. Yet despite its long history, it still throws us some surprises. A decade ago now, it was noticed that the frictional force appears to disappear in galaxies that have a constant density. Our PhD student James Petts has finally shown why this happens and developed a new model to explain the behaviour: http://arxiv.org/abs/1607.04284.