The Evolution of a Globular Cluster
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Shown here is a sequence of artist's impressions explaining the evolution
of a globular cluster. The first graphic shows a globular cluster forming,
where single stars are shown in red and double stars in blue. A globular
cluster then passes through three main phases of evolution, corresponding
to adolescence, middle age, and old age, as shown in the next three
graphics. These "ages" refer to the evolutionary state of the cluster, not
the physical ages of the individual stars.
In the adolescent phase, the stars near the center of the cluster collapse
inward (in more technical parlance this is called "core contraction").
Middle age ("binary burning") refers to a phase when the interactions of
double stars near the center of the cluster prevents it from further
collapse (the stars in green are those currently undergoing
interactions). Finally, old age sets in after the last remaining double
star near the center of the cluster is ejected, and the center of the
cluster collapses inwards ("core collapse"). The final graphic shows a
period of extended old age, when the central region of the cluster expands
and contracts ("gravothermal oscillations) after new double stars are
formed.
New Chandra results suggest that most globular clusters are in adolescence
and a few are in middle age. It was previously thought that most clusters
are in middle age and a few are in old age. [Runtime: 0:19]
View still images
(Credit: Northwestern/W.Finney)
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