Hubble’s ultraviolet survey of 48 globular clusters shows blue straggler stars form mainly through interactions with companion stars, not collisions, reshaping long-standing theories of stellar evolution.
A side-by-side visual of two globular clusters: NGC 3201 (left) and Messier 70 (right).
Photo Credit: ESA/Hubble & NASA
Housed within ancient globular clusters, blue straggler stars twinkle with colours even whiter and brighter than their age would suggest. These "forever young" stars have astronomers scratching their heads for decades. The Hubble study examined images of ultraviolet light emitted by 48 clusters of stars and confirmed the presence of the blue straggler phenomenon as it relates to each star's partner star within the cluster, rather than the rare occurrence of star crashes. The study reveals blue stragglers thrive within peaceful clusters.
According to ESA, globular clusters are old, densely populated swarms of stars where the majority of the constituent stars were formed billions of years ago. Blue stragglers will be differentiated from other stars in their clusters due to their apparent youthful appearance, which is hotter and bluer when compared to other stars. There have been controversies as to the source of these stars because of their defiance of acceptable stellar evolutionary theories. Blue stragglers could have resulted from stellar collisions.
Hubble's ultraviolet study surveyed 48 globular clusters and revealed the presence of 3,000 blue straggler stars. What was even more intriguing was that the denser the globular cluster, the fewer blue straggler stars were found. Conclusively, the sparser the globular cluster, the greater the number of blue straggler stars detected. For sparse globular clusters, a member of a binary system (i.e., two stars that are bound together by their own gravitational force) may gain fuel from its companion or merge to form a single star that appears to be 'younger'. Unfortunately, such encounters do not take place in denser clusters due to the high possibilities of such stars colliding and breaking apart.
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