Globular clusters hold hundreds of thousands of stars in a compact ball hundreds of light years across. From their colours and brightness these stars tell us that they are old – the majority formed at the same time as the Milky Way some 13 billion years ago.
Some globular clusters, however, are younger by several billion years than the majority. Understanding the creation of such star clusters has proven a problem.
The galaxy is known to have settled into its current disk-like shape at this time. This is expected to have drawn in the gas required to form such star clusters.
A study I have been conducting at the Australian National University (ANU) with Gary Da Costa and Dougal Mackey suggests a solution that is not of our galaxy. When we examined the distribution of the younger globular clusters around the Milky Way we saw that these clusters extend out to much greater distances compared with their older counterparts. Furthermore, the younger globular clusters are not scattered randomly about the Milky Way. Rather, they are confined to a plane that meets the disk of our galaxy almost face-on (Fig. 1).
The Milky Way has a flotilla of small satellite galaxies. When the arrangement in space of these satellites was examined, we found that these objects too are in a plane. Our findings show that the plane described by the Milky Way’s satellite...
