The majority of a globular cluster's stars are old and cool, but several hot blue stars show up in this Hubble Space Telescope image of the center of NGC 6397. Many of these stars are believed to be "blue stragglers" or cataclysmic variables, which are the products of stellar mergers or close encounters, respectively. NGC 6397 lies 8,200 light-years from Earth in the constellation Ara. This image is roughly 2 arcminutes (3.8 light-years) wide.
NASA / Hubble Heritage Team (STScI/AURA)