NGC 6397

NGC 6397
A Hubble Space Telescope (HST) image of NGC 6397
Observation data (J2000 epoch)
ClassIX[1]
ConstellationAra
Right ascension17h 40m 42.09s[2]
Declination–53° 40′ 27.6″[2]
Distance7.8 kly (2.4 kpc)[3]
Apparent magnitude (V)+6.68[4]
Apparent dimensions (V)32.0′
Physical characteristics
Mass1.14×105[5] M☉
Radius34 ly[6]
VHB14.2
Metallicity = –1.76[7] dex
Estimated age13.4 ± 0.8 Gyr[8]
Notable featuresSecond closest globular cluster
Other designationsGCl 74,[4] Lacaille III.11, Dunlop 366, Bennett 98, Caldwell 86
See also: Globular cluster, List of globular clusters

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.

  1. ^ Cite error: The named reference hcob849_11 was invoked but never defined (see the help page).
  2. ^ a b Cite error: The named reference aj140_6_1830 was invoked but never defined (see the help page).
  3. ^ a b Salazar, Doris Elen (5 April 2018). "Cosmic 'Yardstick' Measures Distance to One of Universe's Oldest Objects". Space.com. Retrieved 5 April 2018.
  4. ^ a b Cite error: The named reference simbad was invoked but never defined (see the help page).
  5. ^ Cite error: The named reference Vitral+22 was invoked but never defined (see the help page).
  6. ^ distance × sin( diameter_angle / 2 ) = ~34 ly. radius
  7. ^ Cite error: The named reference mnras404_3_1203 was invoked but never defined (see the help page).
  8. ^ a b c Cite error: The named reference eso was invoked but never defined (see the help page).
  9. ^ Jones, K. G. (March 1969). "The search for the nebulae - VI". Journal of the British Astronomical Association. 79: 213–222. Bibcode:1969JBAA...79..213J.
  10. ^ Dunlop, Storm (2005). Atlas of the Night Sky. Collins. ISBN 978-0-00-717223-8.