Star Cluster

The term refers to groups of stars that are either tightly clustered together (Globular) or loosely (Open). The most well known and famous of clusters must be the Seven Sisters or Pleiades in the constellation of Taurus.

Globular Cluster

Globular clusters tend to be old clusters of stars that can range in numbers from 10,000 to anything up to several million. The shape of Globular Clusters are roughly spherical in nature hence where its name comes from (Globe). As mentioned, they tend to be old stars, born not that long after the the beginning of the universe. Although the vast majority of Globular Clusters contain white and yellow stars, they have been a few blue stars in amongst clusters.

Open Cluster

Stars in an Open Cluster tend to be younger stars compared to Globular Clusters and they don`t tend to be as tightly compact. Open Cluster stars all tend to be made of the same material and can be of different ages. At the birth of the Open Cluster, all the stars will be of the same age but they can die at different rates. All the stars aren`t the same size but be varying sizes. They don`t all stay clustered together as they can different away from one another. Of the two types of cluster, these are the more common of the two types with as many as 1000 having been discovered. An Open Cluster whilst it can loose stars as they move away, it can replace the lost stars with new stars from the same material. This is something that a Globular Cluster is unable to do, that is replace a star which is lost. When a Globular Star is lost, its lost and irreplaceable thereafter.

Age of a Cluster

You can determine the age of the star cluster by looking at the colour of the stars that exist in the cluster. All the stars should be roughly the same age. If the cluster is relatively blue then the stars are hot and young and will only last millions of years. If the cluster is yellow then the cluster will last billions of years. If the cluster is red then the cluster is old and can last trillions of years.

If the cluster is predominantly red but there are some blue stars in amongst the stars then its a good sign that there are Vampire Stars in amongst the cluster. In short, vampire stars suck material and fuel from a close star and as they feed and grow, the Vampire Star can appear blue and younger than other stars in the cluster. Ref: Science Channel