The issue is that the ISM is incredibly thing. So it's one of those multiple incredibly large by incredibly small number cases and intuition doesn't work, you'd

The issue is that the ISM is incredibly thing. So it's one of those multiple incredibly large by incredibly small number cases and intuition doesn't work, you'd have to do the actual math. I.e. the timescales could be large enough that if some process could create such an object they could still cross between galaxies.