Exposure: L 10×240 Bin 1, RGB 10×120 Bin2
Telescope: 10″ RC
Camera: QSI 683
Distance: 24,500 Light Years
Size: 23 Arc Minutes
Cluster Type: Globular Class V
Messier 5 is a large globular cluster in the constellation Serpens. At 13 billion years old it is one of the older globular clusters. It is also fairly large at 23 arc minutes but the majority of the cluster extends out about 17 arc minutes. Like most globular clusters, the stars in M5 were formed at about the same time. The largest short lived stars went supernova early in the clusters life cycle and blew out the remaining gas and dust in the region effectively removing the material for future star formation. The remaining stars fell along the main sequence and were smaller and cooler. This cluster also has many RR Lyrae variable stars and a large amount of Blue Stragglers. The RR Lyrae variable star is a star that fluctuates in brightness over a regular period. To date, 97 RR Lyrae variables have been cataloged. The blue stragglers are stars that are bluer and hotter than the surrounding stars in the cluster. This should not happen in a globular cluster as all stars are formed at about the same time. One theory is two stars had an interaction where they lost outer layers and merged in to one newer hotter star. Another theory is that the two stars had an interaction where one’s outer layers were stripped donating this material to the other star.
Globular clusters are rated according to the distribution of their stars. This rating system was formed by Harlow Shapley and Helen Sawyer Hogg and is known as the Shapley-Sawyer Concentration Class. The ratings use Roman Numerals starting at I and ending at XII. Roman numeral I is used for globular clusters with most of their mass at the core with little surrounding stars away from the core. Roman numeral XII is used for globular clusters with a very loose core with minimal structure. M5 is classified as a Class V globular cluster which describes the cluster as having intermediate concentrations of stars.