What are blue stragglers?

Since all stars in open and globular clusters are roughly the same age, a cluster of stars should lie in a unique curve on the Hertzsprung-Russell diagram, with the curve's shape determined by the cluster's age and the positions of the stars determined by their initial masses.

Stars with a mass 2-3 times that of other stars and a location that deviates from the expected curve are known as blue stragglers.

Although the exact formation mechanism of Blue Stragglers is unknown, a popular theory suggests that they arise from the merger of two stars into a single, massive star, which is corroborated by the observation that Blue Stragglers are most frequently found in areas of clusters with high population densities.

Blue stragglers are stars that defy the usual stellar evolution and appear younger and hotter than their surrounding stars. They are the result of stellar interactions such as binary star mergers or mass transfer.