SPACE — Star clusters are groups of hundreds to millions of stars that provide astronomers with important insights through comparisons of the ages and composition of stars. There are three main types of star clusters: globular clusters, open clusters, and stellar associations.
Star clusters form from large interstellar regions filled with gas and dust called molecular clouds. Each of these types of star clusters has different properties that provide different information to astronomers.
Globular star clusters or globular clusters
When seen with the naked eye, globular clusters look like faint streaks of light in the darkness of space. However, a telescope reveals their original form, namely thousands to millions of stars forming a ball with a bright and dense core.
According to the Harvard and Smithsonian Center for Astrophysics, stars in globular clusters formed in the early days of the universe, about 10 billion years ago. This makes them some of the oldest stars in existence.
Due to their very old age, these stars are “metal poor”. This means that the star lacks heavy elements that did not exist in the early universe.
Heavy elements will be created later by supernovae. Because globular clusters have little gas and dust left, they no longer produce new stars.
Astronomers have discovered about 150 globular clusters in the Milky Way galaxy. In contrast, the Andromeda galaxy has about 400, and the M87 galaxy has more than 10,000, according to the Harvard and Smithsonian Center for Astrophysics.
Some well-known globular clusters include Omega Centauri and M13. Omega Centauri is the largest known globular cluster in our galaxy according to NASA. M13 is one of the brightest globular clusters.
Open Cluster
In contrast to globular clusters, open clusters, also known as galactic clusters, do not have a clear shape. Their stars are loosely clustered in amorphous gravitationally bound clusters.
Open clusters contain only hundreds or thousands of stars. This makes open clusters less dense than globular clusters. The open cluster is also much younger.
The oldest stars in open clusters are about a billion years old, according to the Harvard and Smithsonian Center for Astrophysics. Because the cluster is open with fewer stars, it is more loosely bound gravitationally. This means that it is easy for stars in these clusters to migrate away from the group when pulled by other objects, such as giant molecular clouds.
The most famous open cluster is the Pleiades, also known as M45 or Seven Sisters. Other famous open clusters include the Hyades, which is the closest open cluster to Earth, and the Double Cluster, which consists of two side-by-side clusters.
Star association
Stellar associations are groups of tens to hundreds of stars that have similar ages and metals. These groups of stars move in the same direction in the galaxy, but are not bound by gravity.
According to Aaron M. Geller, an astronomer at Northwestern University, some stellar associations likely used to be open clusters, but due to evaporation, they no longer have their gravitational bonds.
2024-02-18 03:30:00
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