An open cluster is a collection of closely related stars that formed from a common molecular cloud of dust and cosmic gases. An open cluster of stars is most commonly found in galaxies with active star formation, such as spiral or irregular galaxies. Open clusters are also known as galactic clusters because they are found within a galaxy’s disk. Open cluster stars are typically small in size, containing a few hundred to a few thousand individual stars on average.
In the Milky Way Galaxy, approximately 1100 open clusters have been discovered, though many scientists believe this is a small fraction of the total number of open clusters that exist. Open clusters can be seen with the naked eye on rare occasions. The open clusters Pleiades, Hyades, and Alpha Persei are all examples of visible open clusters. Other clusters, like the Double Cluster, can only be seen with binoculars or telescopes.
An open cluster contains stars that are relatively young, usually less than a few hundred million years old. The ratio of blue, yellow, and red stars within open clusters can be used to estimate the age of the clusters. Clusters with a higher proportion of blue stars are typically younger than clusters with a higher proportion of red and yellow stars.
Each open cluster star, on average, has a few key characteristics. As a result, open clusters may make it easier for scientists and astrophysicists to study the effects of variables on star properties. In most cases, the age and chemical make-up of the stars in an open cluster are comparable. Furthermore, these stars are usually spaced at approximately the same distance from the earth.
The masses of open cluster stars are usually different. The masses of these stars vary in size, with the largest stars in a young cluster weighing between 80 and 100 solar masses. The mass of smaller stars can be as low as 0.08 solar masses.
Gravity usually binds open clusters together only loosely. However, as they orbit the galactic center, they may become disturbed. When they come into close proximity to gas clouds or other clusters, they often experience this disruption. Internal close encounters may also result in the loss of individual stars.
Some scientists believe that open clusters fade away after a billion years, with some stars drifting to the galaxy’s far side and others drifting to the galaxy’s near side. Depending on the cluster’s initial density, the time period for this disbursement can vary. A cluster that is tightly packed usually lasts longer than a cluster that is loosely packed.