History

The very small and extremely faint globular cluster Koposov 2 was discovered together with another globular cluster (Koposov 1) in 2007 by Sergey E. Koposov et al. on the images of the «Sloan Digital Sky Survey Data Release 5». The discovery was then confirmed with deeper imaging with the 2.2 Meter telescope at Calar Alto Observatory. ^[374]

Physical Properties

The globular cluster is about 33.3 kpc (109'000 light years) away from us and 26.3 kpc (85'800 light years) from the galactic center in the halo of the Milky Way. The diameter of the cluster is about 3 pc (just under 10 light years). Near the center of Koposov 2 we see through it onto a distant background galaxy.

Globular clusters are usually one of the oldest structures in the universe and consist of very old stars. However, the age of Koposov 2 is «only» estimated to be around 5 billion (5×10⁹) years. The age of the cluster and its metal content corresponds roughly to that of the Sagittarius dwarf galaxy. This and the low concentration suggest that this is not a real globular cluster, but an open star cluster that the Sagittarius dwarf galaxy has lost. To confirm this, further spectroscopic studies are necessary to determine whether the speed of the cluster matches that of the Sagittarius dwarf galaxy. ^[375]