Sites of Star Formation Stars form near the spiral arms of our Galaxy. They are only found near spiral arms. H II regions are signatures of star formation because they are produced by O and B stars which have very short lifetimes. Low mass stars are found spread throughout the disk of our Galaxy , they are not confined to the spiral arms. Low mass stars have lifetimes many billions of years long and can wander large distances from their birth sites.
Spiral arms are like compression waves which move through the disk of our Galaxy .
Spiral arms move through the disk at around 20 kilometers per second. So, in 1 million years, a spiral arm moves around 65 light years with respect to the disk material. In 1 billion years, a spiral arm moves around 65,000 light years with respect to the disk material. The most nearby example of a GMC is in the constellation of Orion , the Orion Molecular Cloud .