Globular Clusters

Globular clusters contain thousands to tens of thousands of stars in a spherically bound volume of space around 10 - 50 parsecs across (1 parsec = 3.26 light years or around 3 x 1016 metres). The majority of stars are old, red, evolved, population II stars. Typically, these globular clusters are distributed spherically about our Galaxy including in the Galactic halo. There are approximately 160 globular clusters in our Galaxy as detailed in the catalogues and work of William E. Harris at McMaster University in Hamilton, Canada.

Examples of well-known globular clusters include M3, M13 (the Hercules cluster), M80, 47 Tuc (see Figure 1) and Omega Centauri.

In recent years (since around 2000), another set of clusters have been detected. These are currently known as Super Star Clusters (SSCs) and are typified by Westerlund 1, the Arches and the Quintuplet. These are massive (perhaps up to 50,000 solar masses worth of stars) clusters of young, very bright stars, thought to be globular clusters in the making.

Figure 1: The Hubble Space Telescope's zoomed-in image of the globular cluster, 47 Tucanae.
Credit: NASA, ESA, Digitized Sky Survey (DSS; STcI/AURA/UKSTU/AAO), H. Richer and J. Heyl (University of British Columbia), and J. Anderson and J. Kalirai (STScI)

Which of the following best describes a globular cluster?

A collection of tens to hundreds of old stars
No, globular clusters generally contain more stars than this
A collection of hundreds to thousands of young stars
No, globular clusters generally contain older stars
A collection of tens to hundreds of young stars
No, globular clusters generally contain older stars
A collection of hundreds to thousands of old stars
Yes, globular clusters are old and contain a lot of stars