Key Facts About Globular Clusters
Meaning: A Globular cluster is a type of star cluster that consists of millions of stars tightly held by gravity. The word “globular" stems from the Latin word globulus, which means “a small sphere". The stars in a globular cluster are more than 1010 years old (Population II stars), which are known to be the oldest stars in the cosmos.
Number of globular clusters in the Milky Way Galaxy: 158 approx. (Current)
Diameter: approx. 20 to 100 parsecs
Average mass of a globular cluster (solar masses): 104 to 105
Approx. number of stars in a globular cluster: 105
Average Density of stars in a globular cluster: 0.4 stars per cubic parsec to 1000 stars per cubic parsec
Luminosity (L-solar): 104 to 106
Location in a galaxy: In a halo about a galaxy.
Color of the brightest stars in a globular cluster: Red - red giant stars typcially with an absolute magnitude of -2.
Brightest globular cluster in the Milky Way: Omega Centauri (NGC 5139 in the constellation Centaurus) with an apparent magnitude 3.7
Brightest globular cluster in the local group of galaxies: Mayall II (G1) in the Andromeda galaxy with an apparent magnitude 13.7
Closest globular cluster: Messier 4 (distance: 7,000 light years)
(Image, top left: the image of the Omega Centauri globular cluster taken from the newly installed Wide Field Camera 3 (WFC3) on board Hubble. The WCF3 was installed in May 2009. Image courtesy of Nasa)
Image above: Globular Cluster M80 in the constellation Scorpius. Image courtesy of NASA.