Credit: Aldo Zanetti
Astronomical and Imaging Data
| RA: | 18h 03m 50.51s |
| DEC: | -00° 17′ 51.5″ |
| MAG: | 10.47 |
| Diameter: | 3.4′ |
| Const: | Ser |
| OTA | RC 12″ |
| Focal Length | 2432 |
| Camera | PlayerOne Poseidon M |
| Site | Central Italy |
| Sky Quality | Bortle 4 |
Useful Informations
NGC 6535 is a low-mass, metal-poor globular cluster located in the constellation Serpens. Its low mass and its location close to the galactic bulge make it a particularly interesting subject for studying globular cluster evolution and the potential existence of intermediate-mass black holes (IMBHs).
Key Properties and Structure
NGC 6535 is a relatively small and sparse globular cluster with an estimated mass of about 22,100 solar masses, making it one of the least massive globular clusters in the Milky Way. It is located approximately 22,200 light-years from Earth and about 13,000 light-years from the Galactic Center. The cluster is classified as Class XI, indicating its very loose and sparse concentration of stars.
Despite its small size, NGC 6535 has a surprisingly high mass-to-light ratio, which is a measure of the total mass in a cluster compared to the light it emits. This high ratio, along with a “bottom-light” mass function (a dearth of low-mass stars), has led to the hypothesis that the cluster may harbor a significant amount of dark mass, possibly in the form of a large number of stellar remnants or an intermediate-mass black hole (IMBH). The possibility of an IMBH in this small cluster is particularly intriguing because such objects are typically associated with much more massive stellar systems.
Stellar Populations and Chemical Composition
NGC 6535 is an ancient cluster, with an estimated age of about 12.75 billion years. Its stars are very metal-poor, with a metallicity of just over 1% of the sun’s. This is a common trait of old stellar systems formed in the early universe.
Interestingly, despite its low mass, NGC 6535 has been found to host multiple stellar populations, a phenomenon more typically observed in more massive globular clusters. This is evidenced by an anti-correlation in the abundances of light elements like sodium and oxygen among its stars, suggesting that different generations of stars formed from chemically distinct gas. The cluster also contains a small number of blue stragglers, which are stars that appear to have a younger age than their surroundings, likely formed from stellar collisions or binary star interactions.