🧵 This splendid image from Hubble’s Messier Catalog shows only a portion of Messier 55 (M55 or NGC 6809), a globular cluster containing 100,000 stars. ➡️ science.nasa.gov/mission/hubb... Credit: NASA, ESA, A. Sarajedini (FAU), and M. Libralato (STScI, ESA, #JWST); Image Processing: G. Kober 🔭 🧪

2/ M55, located in the southern Sagittarius some 20,000 ly away, has a diameter of around 100 ly & contains an estimated 100,000 stars with 55 variable ones, found in its central part. The cluster, observed at wide field view, as a whole appears spherical like in the smaller image (lower left).

3/3 Why does it appear spherical? Globular clusters are bound together and supported inside by strong gravity, which gives them the typical spherical shape and maintains a relatively high density of stars at their center.

NOTE: Of course, 100,000 stars in the cluster is a number estimated by scientists using indirect methods based on observations and theoretical models.🔭🧪

Hello, Nereide | thanks for the information and very informative article. Got any explicit information on the particular theoretical models? Again, thank you for a wonderful article ! 🔗📲

1/4 Theoretical models are based on well-established frameworks in stellar physics and astrophysics. Among the main ones, without describing them, there are: - Initial Mass Function (IMF). The widely used model is that of Salpeter (1955). Among the modern variants,⤵️

2/4 there are models such as that of Kroupa (2001) or Chabrier (2003). - Stellar Evolution Models Specific models: Codes such as MESA (Modules for Experiments in Stellar Astrophysics) or PARSEC (PAdova and TRieste Stellar Evolution Code). - Dynamical Models: King's Model (1966)⤵️