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Globular cluster, enormous groupings of hundreds of thousands of stars, that preferentially populate the outer regions of our galaxy and many others, are amongst the most ancient structures in the Universe (in many cases they exceed 10 billion years old). They are probably at least as old as the galaxies whose halos they populate.
For a long time it was believed that globular clusters could not form new stars, given that all the "raw materials" available (gas and dust) had been used up during the first few million years of their long existence. However, already last century, a number of massive blue stars, called "Blue Stragglers", were identified in some of these clusters; whose large mass and consequent short lifetimes indicate that they are much younger than the rest of the red stellar component in globulars.
This unexpected finding was explained by considering that in a region so densely populated by stars, in which the motion of each star is influenced by the complex gravitational pull of all the other stars in the cluster, stars can occasionally collide, producing a blue giant star from the coalescence.
But now the situation is even more complicated, after the discovery, by a group of researchers from McMaster University (Hamilton, Ontario) led by Alison Sills, of a new population of stars that live in globular clusters that are neither created by coalescence nor via the compression of interstellar matter caused by supernova explosions.
As explained by Sills during the CASCA 2011 meeting taking place this week in Ontario, the new population, also made up of young and massive blue stars, could in some way be connected to the birth of the Blue Stragglers, given that they have many properties in common and are found in the same regions of the clusters.
As the new population seems to be formed from material released into space in a non-violent way, and that the fusion of two stars that form a Blue Straggler can be preceded by the release of material, it may be that this is the link between the two classes of star that rejuvenate globular clusters.
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