M5

M5 is located in Serpens about 25,000 light years distant and is one of 160 clusters that orbit the Milky Way core in a spherical halo.  It is estimated that the cluster contains in excess of 100,000 stars which are bound together by their mutual gravitational attraction.  The majority of the stars where formed more than 12 billion years ago making it one of the oldest globular clusters in the Milky Way. The older stars are yellow/red stars giants, whilst the younger blue stars are believed to have been formed from stellar interactions of the densely packed older stars. The concentration of blue stars increases towards the centre where interactions are stronger. Interestingly, it also contains at least 105 low mass periodic variable stars.