Credit: Rodrigo Maeda
Astronomical and Imaging Data
| RA: | 17h 48m 52.70s |
| DEC: | -20° 21′ 36.9″ |
| MAG: | 9.2 |
| Diameter: | 4.4′ |
| Const: | Sgr |
| OTA | GSO RC 8″ Carbon Tube |
| Focal Length | 1624mm |
| Camera | ASI294MC |
| Site | Valparaiso, São Paulo, Brazil |
| Sky Quality | Bortle 5 |
Useful Informations
The globular cluster NGC 6440 is a dense, spherical collection of very old stars located in the southern constellation of Sagittarius. It is an important object for stellar astronomy due to its location and unique properties.
Location and Visibility
NGC 6440 is situated toward the Galactic Bulge of the Milky Way, the dense, central region of our galaxy.
- Distance: The cluster is approximately 27.1 ± 1.3 kilolight-years (8.3 ± 0.4 kpc) from the Sun.
- Discovery: It was first cataloged by astronomer William Herschel on May 28, 1786.
- Apparent Magnitude: With an apparent visual magnitude (V) of about 9.3, the cluster can be observed as a faint, fuzzy patch through a small telescope.
Physical and Stellar Characteristics
As a typical globular cluster, NGC 6440 is a gravitationally bound system of hundreds of thousands to a million stars.
- Mass and Structure: It has a mass greater than 4.42×105 solar masses (M⊙). The cluster’s center is highly concentrated, classified as Shapley–Sawyer Concentration Class V. While dense, it is not a core-collapse cluster.
- Its core radius is very small, about 0.85 light-years (0.26 pc).
- The half-mass radius is approximately 6.6 light-years (2.02 pc).
- Age: Its estimated age is very old, around 11 to 13 billion years ( ≈ 11 Gyr).
- Metallicity: NGC 6440 is considered one of the most metal-rich globular clusters in the galaxy. Its measured iron content is around [Fe/H]=−0.56 dex, placing it relatively close to solar metallicity.
Unique Features: X-ray Sources and Pulsars
NGC 6440 is a significant target for X-ray astronomy due to its large population of exotic stellar remnants.
- Pulsars: The cluster is known to contain numerous pulsars (highly magnetized, rapidly rotating neutron stars). As of 2022, thirteen pulsars have been discovered in NGC 6440, including a few in binary systems like “Black Widow” and “Redback” pulsars, which orbit and ablate a very low-mass companion star.
- Stellar Populations: Recent observations by the James Webb Space Telescope (JWST) have revealed variations in the abundance of light elements like helium and oxygen among the cluster’s stars, providing evidence for Multiple Stellar Populations (MPs), which is a common and intensively studied characteristic of globular clusters.