Credit: Aldo Zanetti
Astronomical and Imaging Data
| RA: | 7h 58m 17.0s |
| DEC: | +26° 15′ 18.6″ |
| MAG: | 17.6 |
| Diameter: | unknown |
| Const: | Gem |
| OTA | Celestron 9.25 Edge HD |
| Focal Length | 2350 |
| Camera | ASI2600MC |
| Site | Central Italy |
| Sky Quality | Bortle 3 |
Useful Informations
Koposov 2 (Ko2) is a low-luminosity stellar system in the constellation Gemini. It is in the outer galactic halo of the Milky Way. Sergey Koposov and his team discovered it in 2007 using data from the Sloan Digital Sky Survey. It is one of the faintest and most extreme star clusters identified orbiting our galaxy.
Physical and Orbital Characteristics
Koposov 2 is approximately 33.3 kiloparsecs (about 109,000 light-years) from Earth. It is about 26.3 kiloparsecs (85,800 light-years) from the Galactic Center. It is small for a globular cluster. Its physical diameter is about 3 parsecs (just under 10 light-years). It has a visual magnitude of 17.60. Observers can see through the center of the cluster to a distant background galaxy.
Scientific Debate on Classification
Initially, it was classified as a globular cluster. Recent research has challenged this based on these factors:
- Age: Most Milky Way globular clusters are over 10 billion years old. Koposov 2 is younger, with an estimated age of 5 billion years.
- Metallicity and Origin: Its chemical composition (metal content) and age are similar to the stars of the Sagittarius Dwarf Galaxy.
- Structure: Many astronomers now classify it as an open cluster. It was likely “stripped” or lost from the Sagittarius Dwarf Galaxy during its tidal interactions with the Milky Way.
Evolutionary State
Koposov 2 has a very short half-mass relaxation time of about 55 million years. This suggests it has undergone significant mass segregation. Its remaining survival time is relatively short. It is undergoing evaporation in the Galactic tidal field.