This cluster is located at a distance of 27.1±1.3kly (8.3±0.4kpc) from the Sun.[3] It is situated toward the galactic bulge of the Milky Way,[3] about 26kly (8.0kpc) from the Galactic Center. The center of the cluster is fairly concentrated, but does not appear to have undergone a core collapse.[7] It has a core radius of 0.85ly (0.26pc), and a half-mass radius of 6.6ly (2.02pc). Observations suggest it is one of the most metal–rich globular clusters in the galaxy, and it is close to solar metallicity.[3] NGC 6440 is a rich target for Astrophysical X-ray sources. As of 2022[update], thirteen pulsars have been discovered in NGC 6440.[3]
References
12Shapley, Harlow; Sawyer, Helen B. (August 1927). "A Classification of Globular Clusters". Harvard College Observatory Bulletin. 849: 11–14. Bibcode:1927BHarO.849...11S.
↑Origlia, L.; etal. (November 2008). "Probing the Galactic Bulge with Deep Adaptive Optics Imaging: The Age of NGC 6440". The Astrophysical Journal Letters. 687 (2): L79–L82. arXiv:0809.3939. Bibcode:2008ApJ...687L..79O. doi:10.1086/593351.
