NGC 6397
| NGC 6397 | |
|---|---|
A Hubble Space Telescope (HST) image of NGC 6397 | |
| Observation data (J2000 epoch) | |
| Class | IX |
| Constellation | Ara |
| Right ascension | 17h 40m 42.09s |
| Declination | –53° 40′ 27.6″ |
| Distance | 7.8 kly (2.4 kpc) |
| Apparent magnitude (V) | +6.68 |
| Apparent dimensions (V) | 32.0′ |
| Physical characteristics | |
| Mass | 1.14×105 M☉ |
| Radius | 34 ly |
| VHB | 14.2 |
| Metallicity | = –1.76 dex |
| Estimated age | 13.4 ± 0.8 Gyr |
| Notable features | Second closest globular cluster |
| Other designations | GCl 74, Lacaille III.11, Dunlop 366, Bennett 98, Caldwell 86 |
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NGC 6397 (also known as Caldwell 86) is a globular cluster in the constellation Ara that was discovered by French astronomer Nicolas-Louis de Lacaille in 1752. It is located about 7,800 light-years from Earth, making it one of the two nearest globular clusters to Earth (the other one being Messier 4). The cluster contains around 400,000 stars, and can be seen with the naked eye under good observing conditions.
NGC 6397 is one of at least 20 globular clusters of the Milky Way Galaxy that have undergone a core collapse, meaning that the core has contracted to a very dense stellar agglomeration.