The story I know is that if you can change the course of such an object by a slight amount early enough, that should be sufficient to cause significant deviations late in its course. Am I mistaken about this, and the force is not strong enough because the deviation is far too small?
For a freely moving mass, yes, though “early enough” can be arbitrarily early depending on how much impulse you have to work with. But stars in a galaxy aren’t freely moving. They’re on highly chaotic trajectories, with characteristic timescales on the order of (very roughly) ~1MYr.
The story I know is that if you can change the course of such an object by a slight amount early enough, that should be sufficient to cause significant deviations late in its course. Am I mistaken about this, and the force is not strong enough because the deviation is far too small?
For a freely moving mass, yes, though “early enough” can be arbitrarily early depending on how much impulse you have to work with. But stars in a galaxy aren’t freely moving. They’re on highly chaotic trajectories, with characteristic timescales on the order of (very roughly) ~1MYr.