Credit: Armen Akopian
Astronomical and Imaging Data
| RA: | 17h 36m 17.23s |
| DEC: | -44° 44′ 07.8″ |
| MAG: | 6.72 |
| Diameter: | 10.2′ |
| Const: | Sco |
| OTA | ASA 1000RC |
| Focal Length | 6500mm |
| Camera | FLI PL16803 |
| Site | El Sauce, Chile |
| Sky Quality | Bortle 1 |
Useful Informations
NGC 6388 is a globular cluster located in the constellation Scorpius. It is one of the most massive and luminous globular clusters in the Milky Way, distinguished by its high stellar density, peculiar stellar population, and an unusually high number of X-ray sources.
Physical Characteristics
- Distance and Apparent Magnitude: Located approximately 33,000 light-years from Earth. With an apparent magnitude of 6.72, it is bright enough to be observed with binoculars.
- Mass and Age: It’s a very massive cluster with an estimated mass of about 1.4×106 solar masses. It’s a very old object, with an age of around 11 billion years.
- Concentration: NGC 6388 is a Shapley–Sawyer Concentration Class III, indicating a highly concentrated core that is not fully resolved from a distance.
Unique Stellar Populations
- Split Red Giant Branch: A key scientific finding in NGC 6388 is the presence of a split red giant branch on its color-magnitude diagram. This indicates at least two distinct stellar populations with different ages or compositions. The presence of these multiple populations suggests that the cluster had a more complex formation history than a single burst of star formation.
- Helium Enrichment: The second generation of stars in NGC 6388 is believed to be significantly enriched in helium, which is thought to be the cause of the split in the red giant branch.
- Oosterhoff Type II Anomaly: NGC 6388 is classified as an Oosterhoff Type II cluster based on its RR Lyrae variable stars, which usually means it should be very metal-poor. However, it has a relatively high metallicity for this class, making it a unique “Oosterhoff-intermediate” cluster.
Black Hole and X-ray Sources
- NGC 6388’s dense core has an unusually high number of low-mass X-ray binaries and other X-ray sources. This abundance is a strong indicator of a dynamically active core, where stars are frequently interacting.
- While an intermediate-mass black hole has been proposed for NGC 6388, conclusive evidence remains elusive. However, the cluster’s high mass and dense core make it a prime candidate for harboring such an object.