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Is the Andromeda Galaxy going to collide with the Milky Way?
I've heard that the Andromeda Galaxy is going to collide with the Milky Way someday. I understand how its radial velocity relative with respect to the Milky Way is determined through its blueshift, but how do we know its tangental velocity? Without knowing that, how can we conclude that a collision is inevitable, rather than a hyperbolic pass or even a closed orbit of the two galaxies around each other, but without actually colliding.
I've heard that the Andromeda Galaxy is going to collide with the Milky Way someday. I understand how its radial velocity relative with respect to the Milky Way is determined through its blueshift, but how do we know its tangental velocity? Without knowing that, how can we conclude that a collision is inevitable, rather than a hyperbolic pass or even a closed orbit of the two galaxies around each other, but without actually colliding.