Australasian Science: Australia's authority on science since 1938

Clusters of Colour

Omega Centauri

Prominent examples of globular clusters in the southern sky include Omega Centauri.

By Christopher Usher and Duncan Forbes

Determining why some globular clusters are blue while others are red is at the heart of understanding how galaxies assembled.

Christopher Usher is a PhD student and Duncan Forbes a Professor in the Centre for Astrophysics and Supercomputing at Swinburne University of Technology.

The full text of this article can be purchased from Informit.

Globular clusters are among the most spectacular objects visible in the night sky with a small telescope. Prominent examples in the southern sky include Omega Centauri and 47 Tucanae.

Since they are made of stars of the same age and chemical composition but different masses, studies of globular clusters in our own galaxy have helped us to understand how populations of stars evolve. Now studies of globular clusters in other galaxies are providing important clues about how galaxies form and evolve.

As some of the oldest objects in the universe, globular clusters are fossils of galaxy formation that provide a unique view of how galaxies assembled. Since they are made up of hundreds of thousands, or even millions of stars, globular clusters can be studied at much greater distances than individual stars.

Massive galaxies have many globular clusters, with our own medium-sized galaxy having about 160 and the most massive galaxies at the centres of galaxy clusters having tens of thousands.

Globular clusters are either blue or red, and why there should be two distinct colour subpopulations has been a matter of debate. The two subpopulations are seen in almost every massive galaxy, suggesting that the process causing the two subpopulations has occurred universally.

Since globular clusters become redder as they age, a large age difference...

The full text of this article can be purchased from Informit.