Abstract:In terms of their energetics, cosmic ray protons are an insignificant by-product of star formation and super-massive black hole growth. However, due to their small mean free path, their coupling with the interstellar
medium is absolute. In fact, they are most likely, the dominant source of momentum, and therefore kinetic force
on galactic scales. By defining an Eddington Limit in Cosmic Rays, we show that the maximum photon luminosity
of bright galaxies and quasars are capped by the production and subsequent expulsion of cosmic ray protons.
Such simple arguments may explain why bright galaxies are faint in comparison to quasars and why super-massive
black holes are relatively mass-less in comparison to galaxies.