Messier 5

Messier 5 (M5) is one of the oldest globular clusters in orbit around the Milky Way.

Like its brother, Messier 3, M5 contains a large number of Cepheid variables and blue stragglers.

Cepheid variables are stars that vary in brightness in a regular, predictable way. This makes it possible for scientists determine the distance to them.

Blue stragglers are stars in an old cluster that appear brighter and bluer than we would expect given the cluster’s age. Scientists are not sure what causes this, but one prominent theory suggests they are the result of star collisions in a densely packed cluster.

Globular clusters are ancient. They are many billions of years old—usually 10 to 13 billion years old—and are almost as old as the universe itself. The stars they contain tend to be very old as well, because star formation inside the cluster has largely ceased. The formation of globular clusters is not well understood. Current research leans toward the idea that they formed from very dense molecular clouds in the early universe.

M5

Distance: 25,000 light years

Number of stars: 100,000

Diameter: 160 light years

Age: 13 billion years