The Great Hercules Globular Cluster

About This Photograph

This is the finest example of a globular star cluster in the northern half of our sky. Also known as M13, this cluster teems with several hundred thousand stars. It is about 145 light years across, and sits at a distance of about 22,000 light years from Earth.

Globular clusters are vast swarms of ancient stars that inhabit the halo of our galaxy, outside of the main disk where most of the stars (and Earth) reside. They can contain anywhere from ten thousand to millions of stars. These stars orbit the collective center of mass of the cluster in a veritable bee hive of motion, and the cluster itself orbits the Milky Way as a distinct object, occasionally plunging right through the main disk and out the other side. Although the cluster appears extremely dense, the distance between individual stars is actually quite large. As a result, stars within them rarely collide, and generally speaking globular clusters survive relatively unscathed by their passage through the galaxy's disk.

Many other galaxies are known to host globular clusters. The Sombrero Galaxy (M104), for instance, has a rich collection.