This image, taken by the Hubble Space Telescope’s Advanced Camera for Surveys (ACS), shows NGC 121 – a ‘globular cluster’ in the Tucana (Toucan) constellation. Globular clusters are large groups of old stars that orbit around the centers of their galaxies.
NGC 121 is located in one of the Milky Way’s neighboring galaxies, the Small Magellanic Cloud (SMC). Discovered in 1835 by English astronomer John Herschel, in recent years the SMC has been studied in unprecedented detail by astronomers who wish to learn more about the formation and evolution of stars.
Stars develop differently, with their formation depending on their original mass. In many clusters, all of the stars seem to have formed at the same time however in others, there are distinct populations of stars that are of different ages.
Through the study of older stellar populations within globular clusters, astronomers can effectively use them to trace the stellar population of their host galaxies. NGC 121 is thought to be around 10 billion years old, making it the oldest cluster in its galaxy as all of the SMC’s other globular clusters are only 8 billion years old or younger.
However, NGC 121 is still several billions years younger than its counterparts in the Milky Way, and in other nearby galaxies such as the Large Magellanic Cloud. The reason for this age gap is not yet known, it could indicate that the cluster’s formation was initially delayed for some reason in the SMC, or that NGC 121 is the sole survivor of an older group of star clusters.
These queries remain unanswered for now. But by using Hubble, astronomers can analyse and observe these clusters and bring themselves one step closer to understanding the complex formation and evolution of distant cosmic objects.
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