... The life-cycles of stars help drive the ecology of our Galaxy, churning, processing, and redistributing matter. Massive stars reach a spectacular evolutionary endpoint - supernovae explosions which blast off their outer layers, violently merging stellar material with the gas and dust of the Milky Way. ... Where are the Milky Way's gas clouds and where are they going? Stars form in gas clouds, and the motion of gas clouds tell us about the size and rotation speed of our own Milky Way Galaxy. ...