Blue straggler

Blue stragglers were first discovered by Allan Sandage in 1953 while performing photometry of the stars in the globular cluster M3.

With masses two to three times that of the rest of the main-sequence cluster stars, blue stragglers seem to be exceptions to this rule.

[3] The resolution of this problem is likely related to interactions between two or more stars in the dense confines of the clusters in which blue stragglers are found.

Field blue stragglers can however be identified in the Galactic halo, since all surviving main sequence stars are low mass.

The two most viable explanations put forth for the existence of blue stragglers both involve interactions between cluster members.

The asteroseismological properties of merged stars may be measurably different from those of typical pulsating variables of similar mass and luminosity.

[10] Observations of blue stragglers have found that some have significantly less carbon and oxygen in their photospheres than is typical, which is evidence of their outer material having been dredged up from the interior of a companion.

Field blue stragglers however can be identified among old stellar populations, like the Galactic halo, or dwarf galaxies.

Sketch of Hertzsprung–Russell diagram of a globular cluster, showing blue stragglers
A Hubble Space Telescope image of NGC 6397 , with a number of bright blue stragglers present [ 5 ]
Video showing the movement of blue straggler stars in globular clusters over time
NGC 6752 , a globular cluster that contains a high number of blue straggler stars [ 8 ]
47 Tucanae contains at least 21 blue stragglers near its core. [ 6 ]