A program on the Science Channel last night talked about black holes in the
center of galaxies. It also mentioned that the galaxy in Andromeda M31 is
moving toward us and will therefore collide with our galaxy some time in the
future--They showed simulations. Is this true? You can get the radial
velocity from the Doppler shift, but how can they know the angular velocity?
Isn't it more likely that it's just gravitationally bound?