Credit: Aldo Zanetti
Astronomical and Imaging Data
| RA: | 17h 27m 08.50s |
| DEC: | -07° 05′ 35.0″ |
| MAG: | 13.1 |
| Diameter: | 4.95′ |
| Const: | Oph |
| OTA | RC 12″ |
| Focal Length | 2432mm |
| Camera | Moravian C3 61000 |
| Site | Central Italy |
| Sky Quality | Bortle 3 |
Useful Informations
NGC 6539 is a globular cluster located in the constellation Serpens (the Serpent). It is an important object for studying the properties of the Galactic bulge because it resides in its outer parts.
Physical Characteristics
- Age and Metallicity: NGC 6539 is considered a metal-rich globular cluster, with a metallicity ([Fe/H]) of approximately -0.66. This is higher than most globular clusters, which are typically very metal-poor. Its relative richness in heavier elements indicates that its stars were formed from gas that had already been enriched by previous generations of stars. This supports the theory that the Galactic bulge formed earlier and more rapidly than the outer halo. The cluster’s estimated mass is about 536,000 solar masses.
- Diameter and Magnitude: The cluster has an apparent visual magnitude of approximately 9.33, making it a faint object that is difficult to see with the naked eye and requires a small telescope. Its apparent angular diameter is about 7.9 arcminutes, which corresponds to a physical diameter of roughly 60 light-years.
- Distance and Location: NGC 6539 is located approximately 26,600 light-years from the Sun and about 10,000 light-years from the Galactic Center. Its position in the outer Galactic bulge, a region of high interstellar dust and gas, causes significant extinction, which makes it appear fainter and redder than it truly is.
Variable Stars and Dynamics
NGC 6539 is home to a number of variable stars, with a dozen being identified as long-period variables. It is also a known host of a millisecond pulsar (a rapidly rotating neutron star), which was discovered in 1990. The presence of such objects is a testament to the high stellar density within the core of globular clusters, where stellar encounters and interactions are more frequent.