Globular cluster M5, optical image. A globular cluster is a huge ball of stars that orbits the nucleus of our Milky Way galaxy. Other galaxies have also been found to have a population of orbiting globular clusters. The stars in a globular cluster are very old, amongst the oldest stars in the galaxy. M5 is estimated to be about 13 billion years old, only 0.7 billion years younger than the universe itself. M5 is a large cluster, containing as many as half a million stars within a diameter of some 165 light years. It lies 24,500 light years from Earth in the constellation Serpens.