Archive of Astronomy Questions and Answers

What is a globular cluster, and are there any near the Milky Way?

A globular cluster is a roundish collection of some 100,000 to several million stars which orbit the Milky Way. There are some 125 of these star systems known to be orbiting the Milky Way, but there are probably more than this because some parts of the Milky Way cannot be easily seen from our vantage point. A good upper limit is probably 160 or so globular clusters. Some galaxies such as M87 in Virgo, have 10,000 globular clusters. The nearest, prominent globular cluster to the Earth is M 13 in the constellation Hercules at a distance of 24,900 light years. The globulars 47 Tucana ( distance = 16,500 light years) and Omega Centauri ( distance = 16,200 light years) are also quite spectacular. Have a look at the Messier Image Archive for images of many different globular clusters, or have a look at Messier 13 for an image and additional information about this cluster.

These clusters orbit the Milky Way, not in the plane of the Milky Way, but in the so-called halo region located above and below the flattened disk of our galaxy. They contain some of the oldest stars known, with ages from 9 to 16 billion years. Currently there is a major controversy over the age estimates for these systems being larger than the age of the universe determined from its expansion rate. Evidently, either the stellar astronomers or the cosmologists getting the data from the Hubble Space Telescope are being affected by some 'error' which as yet has not been identified. The universe cannot contain objects older than it is itself!