NGC 6397 | |
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![]() A Hubble Space Telescope (HST) image of NGC 6397 | |
Observation data (J2000 epoch) | |
Class | IX[1] |
Constellation | Ara |
Right ascension | 17h 40m 42.09s[2] |
Declination | –53° 40′ 27.6″[2] |
Distance | 7.8 kly (2.4 kpc)[3] |
Apparent magnitude (V) | +6.68[4] |
Apparent dimensions (V) | 32.0′ |
Physical characteristics | |
Mass | 1.14×105[5] M☉ |
Radius | 34 ly[6] |
VHB | 14.2 |
Metallicity | = –1.76[7] dex |
Estimated age | 13.4 ± 0.8 Gyr[8] |
Notable features | Second closest globular cluster |
Other designations | GCl 74,[4] Lacaille III.11, Dunlop 366, Bennett 98, Caldwell 86 |
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.[9] It is located about 7,800 light-years from Earth,[3] making it one of the two nearest globular clusters to Earth (the other one being Messier 4). The cluster contains around 400,000 stars,[8] and can be seen with the naked eye under good observing conditions.[10]
NGC 6397 is one of at least 20 globular clusters of the Milky Way Galaxy that have undergone a core collapse,[8] meaning that the core has contracted to a very dense stellar agglomeration.
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