Blue straggler
In astronomy, a “ blue straggler ” (translatable by “slow blue”) indicates a abnormally blue star in a stellar Amas. Indeed, when one makes diagram “color-magnitude” of cluster (i.e which one places in a diagram for all stars of the cluster the Indice of color according to the magnitude or Luminosité), it appears sometimes stars which are indeed members of the cluster but which, being given the age of the cluster, should have already disappeared on the sequence from the giant reds, or to be itself extinct in white dwarf . It is the result of the normal stellar evolution seeing stars blue (and thus more massive) of a population of a cluster, born all at the same moment, to disappear more quickly, since these stars more quickly burn their tank of Hydrogène. The “blue stragglers”, they, go apparently to counter-current of this effect. One thinks in fact that they are the result of a mass transfer in a binary star when the primary star approaches the end of its life and that its ray increases. The secondary star, usherette, become thus suddenly more massive than it was it initially, and is thus “renovated”, and thus more blue, whereas its true age is that of the cluster.
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