What is the difference between a globular cluster and an open cluster?

They both contain stars but what’s the difference?

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The Pleiades are the most famous open cluster 

The Pleiades are the most famous open cluster. Image Credit: NASA

Asked by Jack Bannister

Both are types of star clusters, but the major differences come down to the age of the stars found within them, where they can be found in a galaxy and their shape.

As their name suggests, globular clusters are globule-shaped balls of hundreds of thousands of stars all crammed into an area a few hundred light years across. They live in the halo of our galaxy and orbit the galactic centre. They are very old, at 12 to 13 billion years, while a few form the cores of smaller galaxies that have been cannibalised by the Milky Way.

On the other hand, open star clusters live in the spiral arms of the galaxy and are very young – the youngest are just several million years old, while the oldest can reach a few billion years old. The stars form together in a cluster inside a nebula and, as they age, they gradually disperse.

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