Messier 55 – Specter Cluster

Difficult to spot from the northern hemisphere, Messier 55 (M55) lies about 17,600 light years away in the southern part of the southern constellation Sagittarius. The stars in M55 are what astronomers call “metal poor.” That means they contain very little other than hydrogen and helium.

Globular clusters are ancient collections of stars that are gravitationally bound together in a spheroidal shape. Some are almost as old as the universe itself. They can contain anywhere from tens of thousands of stars to millions of stars. The stars they house 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. Some larger globular clusters may once have been dwarf galaxies whose larger star populations were stripped away from the core by larger galaxies.

M55 Facts

Distance: 17,600 light years

Number of stars: 100,000

Diameter: 96 light years

Age: 12.3 billion years