The Milky Way is on a path of destruction. In 5 billion years, it will smash into Andromeda, the biggest spiral galaxy in the neighborhood. The collision will create legions of giant new stars, up our quotient of radiation-spewing supernovas, and feed a lot of matter into the mouths of massive, massive black holes. Beyond that, there are a whole lot of maybes and probablys.

The quest to understand exactly how the bust-up will happen is giving scientists a good excuse to rubberneck elsewhere. Using images from two NASA space telescopes—the Spitzer, which captures infrared, and the Galaxy E...