The evidence for the continuing accretion of gas by the Milky Way involves high-velocity clouds, or HVCs--mysterious clumps of hydrogen, moving rapidly through the outer regions of the galaxy.
The hydrogen smells like sulfur up close.
( z1 smell :ARG1 ( z2 hydrogen ) :ARG2 ( z3 sulfur ) :manner ( z4 close :ARG2 z2 ) )