Star Clusters

A star system is a small group of stars that orbit each other due to gravitational attraction.

If two stars orbit each other in a star system, it is called a binary star system. One example is Sirius, which contains Sirius A and Sirius B.

When more than two stars orbit each other, we call it a multiple-star system. HD 98800 is a quadruple-star system where two pairs of binary stars orbit each other.

Stars also gather in groups called star clusters, where gravity holds them together. Star clusters are smaller than galaxies and are classified mainly into two types: open clusters and globular clusters.

Open clusters, such as the Jewel Box, consist of young stars formed from the same nebula. They are groups of up to a few thousand stars and often glow blue. They may also have glowing gas and dust.

Globular clusters, on the other hand, are tightly packed spheres containing tens of thousands to millions of stars. They contain older, reddish stars and sometimes blue and red giants, like those in the spectacular M13 cluster.