  The growth of galaxies in the early Universe is driven by accretion of
circum- and inter-galactic gas. Simulations predict that steady streams of cold
gas penetrate the dark matter halos of galaxies, providing the raw material
necessary to sustain star formation. We report a filamentary stream of gas that
extends for 100 kiloparsecs and connects to the massive radio galaxy 4C 41.17.
The stream is detected using sub-millimeter observations of the [CI] line of
atomic carbon, a tracer of neutral atomic or molecular hydrogen gas. The galaxy
contains a central gas reservoir that is fueling a vigorous starburst. Our
results show that the raw material for star formation can be present in cosmic
streams outside galaxies.
