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How are open clusters different from globular clusters?
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Star cluster
Centre of star cluster 47 Tucanae (NGC 104), showing the colours of various stars.
Most of the brightest stars are older yellow stars, but a few young blue stars are also visible. This picture is a composite of three images taken by the Hubble Space Telescope.
Open clusters and globular clusters differ significantly in their physical characteristics, distribution, and longevity.
Key Differences
- Structure and Appearance: Open clusters are characterized by a loose, sparse appearance and relatively large core radii. In contrast, globular clusters are approximately spherical, densely packed groups of stars.12
- Mass and Population: Open clusters are smaller and less massive, typically containing tens to a few thousand stars with masses around 50 solar masses. Globular clusters are significantly more massive and contain much larger stellar populations.1
- Distribution: Open clusters are concentrated along the plane of the Galaxy, often associated with spiral arms. Globular clusters typically populate the galactic halo.12
- Age and Composition: Open clusters are generally young, often younger than 200 million years, and contain stars with heavy-element abundances similar to or greater than the Sun. Because they are not strongly gravitationally bound, they are susceptible to tidal forces that often dissipate them within a few hundred million years.1
Would you like to learn more about how astronomers determine the ages of these clusters using colour-magnitude diagrams?1