... Tonight's Sky . ... Monstrous cloud boomerangs back to our galaxy . Though hundreds of enormous high-velocity gas clouds whiz around the outskirts of our galaxy, this so-called "Smith Cloud" is unique because its trajectory is well known. ... Astronomers long thought that the Smith Cloud might be a failed, starless galaxy, or gas falling into the Milky Way from intergalactic space. ... Instead, the cloud appears to have been ejected from within the Milky Way and is now boomeranging back. ...