Blue straggler - bigger and bluer star formation

A blue straggler is a main-sequence star in an open or globular cluster that is more luminous and bluer than stars at the main sequence turnoff point for the cluster.
Blue stragglers were first discovered by Allan Sandage in 1953
Indian researchers found that half of the blue stragglers in their sample are formed through mass transfer from a close binary companion star, one third are likely formed through collisions of 2 stars, and the remaining are formed through interactions of more than 2 stars.

Formation Process

A bunch of stars born at the same time from the same cloud form a star cluster.
As time passes, each star evolves differently depending on its mass.
The most massive and bright stars evolve and move off the main sequence creating a bend in their track, known as the turnoff.
Some stars seem to be hotter than the turnoff of the parent cluster, they are termed “Blue Stragglers”