The cosmic riches of Messier 69
NASA’s Hubble Space Telescope has snapped a dazzling image of the globular cluster Messier 69, or M 69 for short.
Essentially, globular clusters are dense collections of old stars. In the picture below, foreground stars appear big and golden when set against the backdrop of the thousands of white, silvery stars that make up M 69.
Another aspect of M 69 lends itself to the bejeweled metaphor: As globular clusters go, M 69 is one of the most metal-rich on record.
In astronomy, the term "metal" has a specialized meaning: it refers to any element heavier than the two most common elements in our Universe, hydrogen and helium.
The nuclear fusion that powers stars created all of the metallic elements in nature, from the calcium in our bones to the carbon in diamonds. Successive generations of stars have built up the metallic abundances we see today.
Because the stars in globular clusters are ancient, their metallic abundances are much lower than more recently formed stars, such as the Sun. Studying the makeup of stars in globular clusters like M 69 has helped astronomers trace back the evolution of the cosmos.
M 69 is located 29 700 light-years away in the constellation Sagittarius (the Archer). The famed French comet hunter Charles Messier added M 69 to his catalogue in 1780. It is also known as NGC 6637.