Astronomy & Cosmology -
The globular cluster Palomar 12 was almost certainly captured from the Sagittarius Dwarf about 1.7 billion years ago. It is relatively young compared to most of the clusters in the Milky Way. It is about 64,000 light years away, about 324 light years across, and about 6.5 billion years old. While very large in diameter, the component stars are rather well spread out compared, say, to to Omega Centauri. In 1957, it was classified in error as a dwarf spheroidal galaxy in its own right by Fritz Zwicky, and called Capricornus Dwarf.
Omega Centauri is the largest known cluster in the Milky Way at about five million Solar masses, and containing some ten million stars. It is about 17,000 light years away, 170 light years across, and visible only in the southern hemisphere except during parts of May and June. There is evidence that it is in fact the central core of a dwarf galaxy that the Milky Way captured some time in the past. It is about twelve billion years old. It also appears to harbor its own intermediate mass black hole of about 40,000 solar masses.
Messier 80 is a densely populated globular cluster about 32,600 light-years away, about 96 light-years in diameter, and containing several hundred thousand stars. It contains a large number of so-called "blue stragglers". These are believed to be stars that have lost part of their outer layers from collisions or close encounters with other stars due to the high stellar density, particularly in the core of the cluster. It is intrinsically very bright and is seen easily with binoculars or a small telescope despite its distance from us.
What Is A Globular Cluster?
Globular clusters are approximately spherical groupings of from tens of thousands up to millions of very old, mainly Population II stars. The clusters tend to range from about 10 to 30 light years in diameter, although some are much larger, and orbit their parent galaxy in the halo. The stars are mostly quite small, less than two solar masses, and yellow, like the Sun, to red. Larger, hotter stars would already have finished their life spans in supernovae or as white dwarfs. Globular clusters are very old, having formed around one to two billion years or so after the big bang, but their origins are hotly debated. It appears that the Milky Way is currently capturing globular clusters from the nearby Sagittarius Dwarf and Canis Major Dwarf galaxies.