NGC 6440
Globular cluster in the constellation of Sagittarius
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NGC 6440 is a globular cluster of stars in the southern constellation of Sagittarius. It was discovered by German-English astronomer William Herschel on 28 May 1786. With an apparent visual magnitude of 9.3 and an angular diameter of 4.4′, it can be observed as a fuzzy blob when viewed through a small telescope.[4] Its Shapley–Sawyer Concentration Class is V.[1]
| NGC 6440 | |
|---|---|
HST image of NGC 6440 | |
| Observation data (J2000 epoch) | |
| Class | V[1] |
| Constellation | Sagittarius |
| Right ascension | 17h 48m 52.67s[2] |
| Declination | −20° 21′ 34.5″[2] |
| Distance | 27.1 ± 1.3 kly (8.3 ± 0.4 kpc)[3] |
| Apparent magnitude (V) | 9.3[4] |
| Apparent dimensions (V) | 4.4′[4] |
| Physical characteristics | |
| Mass | > 4.42×105[3] M☉ |
| Metallicity | [Fe/H] = −0.56[3] dex |
| Estimated age | ≈11 Gyr[5] |
| Other designations | NGC 6440[6] |
This cluster is located at a distance of 27.1 ± 1.3 kly (8.3 ± 0.4 kpc) from the Sun.[3] It is situated toward the galactic bulge of the Milky Way,[3] about 26 kly (8.0 kpc) 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 0.85 ly (0.26 pc), and a half-mass radius of 6.6 ly (2.02 pc). 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]
