Credit: Aldo Zanetti
Astronomical and Imaging Data
| RA: | 18h 24m 32.81s |
| DEC: | -24° 52′ 11.2″ |
| MAG: | 6.79 |
| Diameter: | 11.2′ |
| Const: | Sgr |
| OTA | Celestron 9.25 Edge HD |
| Focal Length | 2350 |
| Camera | ASI2600MC |
| Site | Central Italy |
| Sky Quality | Bortle 3 |
Useful Informations
NGC 6626, also known as Messier 28 (M28), is a globular star cluster located in the constellation Sagittarius. It’s a dense, ancient stellar system with several notable characteristics that make it a subject of scientific interest.
Key Properties and Composition
M28 is a very old globular cluster, with an estimated age of about 12 billion years. It’s located approximately 18,000 light-years from Earth and has a total mass of around 551,000 solar masses, spanning a diameter of about 60 light-years. The cluster contains at least 50,000 stars, with the brightest stars being around 15th magnitude. It is classified as a Class IV globular cluster, indicating an intermediate concentration of stars with a visible but somewhat spread-out core.
One of its most important features is its metallicity, which is low compared to the sun. This means it has a smaller proportion of elements heavier than helium. Recent spectroscopic studies have shown that the cluster’s stars are not chemically uniform but instead show a spread in light elements like oxygen, sodium, and aluminum, suggesting the presence of at least three distinct sub-populations of stars. This phenomenon, known as multiple populations, is a key area of research in globular cluster formation and evolution.
Pulsars and Neutron Stars
M28 is particularly famous for being the first globular cluster where a millisecond pulsar was discovered. A millisecond pulsar is a rapidly rotating neutron star that emits a beam of electromagnetic radiation. The first one found in M28, designated PSR B1821-24, rotates at an incredible speed, completing one rotation in just about three milliseconds. Since its initial discovery in 1986, many more millisecond pulsars have been found within the cluster, making M28 a significant target for studying these exotic stellar remnants and their formation processes in dense environments.