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.
Hydrogen wasn't found in the Milky Way before this.
( z1 find :polarity - :ARG1 ( z2 hydrogen ) :location ( z3 galaxy :name ( z4 name :op "Milky" :op "Way" ) ) :time ( z5 before :op ( z6 this ) ) )