Extragalactic Cosmic Rays
10 eV protons (r~1Mpc) cannot be contained in Galaxy long enough to remove original direction, => travel in straight lines from outside Galaxy.
What conditions/geometry required to produce energy density of cosmic rays observed at these energies?
Notes:
The radius of curvature for protons with energies of about 1e20eV is about 1Mpc. This is much larger than the scale of our Galaxy, therefore the directions of cosmic rays we observe in these particles are approximately those of the directions outside the Galaxy. Another way of looking at this is to say that the particles cannot be contained for long enough within the Milky Way to remove the original direction.
We will hypothesise some reasonable sources of cosmic rays, predict their output and see if this is consistent with observed levels of cosmic ray flux.