(M15, NGC 7078)
(globular cluster with collapsed core)
Messier 15 (M15 or NGC 7078) is a
globular cluster, unusual for the dense packing of stars in the center
(the profile of the density rising all the way to the center),
apparently having experienced a core collapse,
a collapse of the middle region of a globular cluster.
(Globular clusters typically have a central region of a high but
constant density of stars.)
It includes 100,000+ stars, including a planetary nebula,
some pulsars, and variable stars.
Its estimated age is 12 gigayears and it
has a diameter of about 175 ly.
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