Blue straggler stars within the globular cluster M55 are circled in this color-magnitude diagram, which plots the color and overall brightness of stars of the same age. Middle-aged, main-sequence stars fall along the thick band spanning from the lower-right to the center of this image. When they evolve to red giants, they start climbing up the thin band to the upper-right. Rejuvenated blue stragglers are stars so massive (and therefore short-lived) that they seem like they should already be on the red giant branch, but they instead form their own extended population along the main sequence.