These beautiful stellar groupings are spattered across the cosmos

Written by Nikole Robinson

While there are many fascinating objects in the night sky to turn a telescope towards, star clusters are bountiful starscapes – W glittering clumps of hundreds to millions of stars bound together by their collective gravity and travelling through space as one. As the stars that make up a cluster were born from the same cloud of gas and dust, they have similar ages and chemical compositions. This makes star clusters useful in the study of stellar evolution, as their member stars can be compared to see how stars of different sizes and masses change over time.

Star clusters fall into two categories: open and globular. Globular clusters are older – many over 10 billion years old – with an abundance of yellow and red giant stars. They possess thousands of individual stars and are particularly dense nearer their cores, with immense gravitational forces pulling them into roughly symmetrical spherical shapes. These sparkling stellar collections are most likely to be found in the halos of galaxies, orbiting far from the centre above and below the galactic plane. The Milky Way has around 150 globular clusters in orbit, but the giant elliptical galaxy Messier 87 is known to possess over 1,000 of these star-studded objects, revealing that they’re common across the cosmos.

Open clusters are much less dense, at most made up of a few thousand stars, with the less intense gravity meaning they’re loosely bound together and don’t take on a distinct shape. The stars that make up open clusters are younger, hotter blue stars, and some of these clusters possess enough leftover stellar material that star formation can still take place. Open clusters are found in the discs of galaxies, particularly near spiral arms. Unlike more stable globulars, open clusters are short-lived, with the members likely to drift apart naturally over millions of years or be affected by gravitational perturbations that break up the group.