![]() The name of this cluster belies our early ignorance about their true nature: Omega Centauri was named as if it were a star in the constellation Centaurus! To the unaided eye, it is very stellar in appearance – a bright point of light without any extended structure. The first globular star cluster was catalogued by Ptolemy in 150 AD, known today as Omega Centauri. Large galaxies, like the massive elliptical galaxy M87, have more than 10,000 globular clusters orbiting them. The Milky Way has 157 known globular clusters, 1 though we expect that there could be as many as 200, with the missing globular clusters obscured from our view on the far side of the Milky Way. They exist in the vicinities of large galaxies, orbiting the galaxy in a spherical swarm like a cloud of bees or mosquitoes. Globular star clusters are collections of stars, typically hundreds of thousands to a million stars, which remain mutually bound together by their collective gravitational attraction. Our understanding of the nature of globular star clusters is an excellent illustration of this process. As such, our understanding of the Universe is always bound by our current state of knowledge (what we have already discovered) and limited by both the capabilities of our devices and by chance – were we paying attention when a rare event happened? The net result is that over time our understanding of astronomical phenomena dramatically changes and evolves. We are confined to our own small corner of the Universe, probing outward with a meagre suite of instruments designed to detect and measure what our senses cannot. Experiments cannot be controlled, nor can they be repeated. The difference between the Universe and a conventional laboratory is that researchers are highly constrained by the fact that the Universe is not a hands-on experiment everything we discover is based on non-interactive observations. In astronomy, there are very few laboratory experiments that match the conventional image of laboratories and experiments that are conjured in people’s heads when you say the word “science.” The reason is simple: in astronomy, the Universe is our laboratory. Ideas about natural phenomena and the laws that govern the way Nature works grow organically from the mixing of results and experiments that are carried out in each of these three tiers. The modern scientific enterprise is one that is built around mutually supportive tiers of endeavour: experiment, theory and, increasingly, computation. Associate director of CIERA at Northwestern University Shane Larson explores the role of globular star clusters within the Universe.
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