but if we had the energy of our sun available, surely we could redirect the path of such an object if detected early enough?
Momentum is the limiting factor. Even redirecting all of the sun’s light in the same direction only gets you about 1018 N of force. That’s enough to accelerate a solar mass by a whopping 10−13 m/s2, so you’re going to need to see it coming millions of years out. Doing better than that would require somehow ejecting a significant amount of reaction mass from the solar system.
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.
Momentum is the limiting factor. Even redirecting all of the sun’s light in the same direction only gets you about 1018 N of force. That’s enough to accelerate a solar mass by a whopping 10−13 m/s2, so you’re going to need to see it coming millions of years out. Doing better than that would require somehow ejecting a significant amount of reaction mass from the solar system.
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.