Blue straggler formation (artist's impression)

This is an artist's concept of a close binary pair of stars that are merging to form a blue-straggler-class star. Blue stragglers are so named because they seem to be lagging behind in their rate of aging compared with the population from which they formed. The merger stirs up hydrogen fuel and causes the resulting more massive star to undergo nuclear fusion at a faster rate, causing it to burn hotter and bluer. Probing the star-filled, ancient hub of our Milky Way, the Hubble Space Telescope has found blue stragglers for the first time within our galaxy's bulge.