This is a pretty good question. There is a limit to the changes in the momentum of cold dark matter before it produces visible effects in galaxies of different

This is a pretty good question. There is a limit to the changes in the momentum of cold dark matter before it produces visible effects in galaxies of different ages. Explosive processes in the dark matter sector must be rare, whatever their mechanism and whatever their daughter products (even if it quickly decays to cold dark matter again, but on a different trajectory).