Credit: Jim Fordice
Astronomical and Imaging Data
| RA: | 17h 30m 39.00s |
| DEC: | -31° 35′ 43.9″ |
| MAG: | 16.0 |
| Diameter: | 0.7′ |
| Const: | Sco |
| OTA | Planewave CDK24 |
| Focal Length | 3962mm |
| Camera | QHY 600M |
| Site | Río Hurtado, Chile |
| Sky Quality | Bortle 1 |
Useful Informations
Terzan 4 is a globular cluster located deep within the bulge of the Milky Way galaxy, making it a valuable subject for studying the oldest components and formation history of our galaxy.
Galactic Location and Extinction
The cluster is situated in the direction of the constellation Scorpius. It resides at an estimated distance of approximately 26,000 light years from Earth, placing it remarkably close to the actual Galactic Center, which is also about 26,000 light years away. This proximity to the central region of the Milky Way is the defining observational challenge for Terzan 4.
- Extinction: The cluster lies behind dense clouds of interstellar gas and dust concentrated in the Galactic Bulge. This material causes heavy extinction, which is the absorption and scattering of starlight, particularly in the visible spectrum. This extinction significantly dims and reddens the cluster’s light, making it very faint in ground-based optical observations, which is why it was not discovered until the 1960s by Agop Terzan.
- Observation: Detailed studies, such as those conducted using the Hubble Space Telescope, must utilize infrared and longer wavelength optical instruments to penetrate the obscuring dust clouds, allowing astronomers to resolve individual stars and accurately measure the cluster’s properties.
Physical and Stellar Characteristics
Terzan 4 is a dense, massive collection of millions of stars held together by their mutual gravitational attraction in a roughly spherical shape.
- Age and Metallicity: Scientific analysis of the cluster’s stars indicates that Terzan 4 is an extremely old globular cluster. It is classified as metal-poor, meaning its stars contain a low abundance of elements heavier than hydrogen and helium (astronomers refer to all elements heavier than helium as “metals”). This low metallicity is a characteristic feature of very old stellar populations, which formed before successive generations of massive stars had created and dispersed significant amounts of heavy elements into the galactic medium.
- Dynamical State: The intense gravitational environment created by the high density of stars in its core makes Terzan 4, like other inner bulge clusters, a site of frequent stellar interactions. These interactions can lead to the formation of exotic stellar systems, such as low-mass X-ray binaries.
- Structural Parameters: Measurements of its structure, such as its concentration parameter, classify it as a relatively compact globular cluster, consistent with other clusters located near the Galactic Bulge.