The globular cluster Messier 15 in
Pegasus, not visible to the naked eye,
provides a fine contrast to visually brighter
Messier 13. Thirty-four thousand light years away, 70 light
years across, even more massive than Messier 13 (550,000 solar
masses), it is one of the most compact, centrally condensed
clusters known, and is suspected of harboring a medium-mass
black hole. Nearly 12
billion years old, it has an iron content (compared to hydrogen) just
one percent of that of the Sun.
University of Illinois Prairie Observatory.
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