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Open and Globular Star Clusters

Star Clusters Fact

What is a 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. They should not be considered as being unique to our galaxy, the Milky Way. A global cluster has been found in NGC 4874 Springer

What is a Globular Star 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.

Globular Clusters tend to be found nearer the Galactic Centre of the galaxy whereas Open ones tend to be further out. The Pleiades Cluster is a good example of an open Cluster, they are in the opposite direction to the centre of the Galaxy, Sagittarius A*. For the opposite, Messier 80 is a Globular Cluster in the constellation of Scorpius.

Some galaxies do not have a Supermassive black hole at its heart, some will have a Globular Cluster at the heart instead.

Omega Centauri, Largest Globular Cluster

The largest Globular Cluster in the galaxy is Omega Centauri located in Centaurus galaxy. The Globular Cluster is estimated to have at least 10 millions stars of different colours and sizes. The combined mass is equivalent to four million solar masses. The picture below is taken from the Hubble space telescope. Some of the blue stars are likely to be blue stragglers, or vampire stars.

Omega Centauri

What is an Open Star 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.

Hyades, Local Star Cluster

The Hyades open star cluster is a local star cluster to us at around 153 light years. The cluster is located in the constellation of Taurus, the bull. The Hyades includes some of the well know Taurian stars such as Ain also known as Epsilon Tauri. Although located near Aldebaran, Aldebaran is not a member of the Hyades. Ain is of particular interest because has an orbiting exoplanet.

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. These vampire stars are referred to as Blue Stragglers. 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

NameMessier_TypeConstellation
Messier 72 (NGC6981)Globular ClusterAquarius
Messier 2 (NGC 7089)Globular ClusterAquarius
Westerlund - 1Star ClusterAra
Messier 36 (NGC1960)Open ClusterAuriga
Messier 37 (NGC2099)Open ClusterAuriga
Messier 38 (NGC1912)Open ClusterAuriga
Praesepe, the Beehive Cluster (M44, NGC2632)Open ClusterCancer
Messier 67 - King Cobra ClusterOpen ClusterCancer
Messier 3 (NGC5272)Globular ClusterCanes Venatici
Messier 41 (NGC2287)Open ClusterCanis Major
Messier 30 (NGC7099)Globular ClusterCapricornus
Westerlund - 2Star ClusterCarina
Messier 103 (NGC581)Open ClusterCassiopeia
Messier 52 (NGC7654)Open ClusterCassiopeia
Pearl ClusterClusterCentaurus
Omega CentauriGlobular ClusterCentaurus
Messier 53 (NGC5024)Globular ClusterComa Berenices
Jewel Box Star ClusterOpen ClusterCrux
Messier 29 (NGC6913)Open ClusterCygnus
Messier 39 (NGC7092)Open ClusterCygnus
Tarantula Nebula (NGC2070)Globular ClusterDorado
Messier 35 (NGC2168)Open ClusterGemini
Messier 92 (NGC6341)Globular ClusterHercules
The Great Hercules Globular Cluster (M13, NGC6205)Globular ClusterHercules
Messier 68 (NGC4590)Globular ClusterHydra
Messier 48 (NGC2548)Globular ClusterHydra
Messier 79 (NGC1904)Globular ClusterLepus
Messier 56 (NGC6779)Globular ClusterLyra
Messier 50 (NGC2323)Open ClusterMonoceros
Messier 62 (NGC6266)Globular ClusterOphiuchus
Messier 107 (NGC6171)Globular ClusterOphiuchus
Messier 14 (NGC6402)Globular ClusterOphiuchus
Messier 19 (NGC6273)Globular ClusterOphiuchus
Messier 12 (NGC6218)Globular ClusterOphiuchus
Messier 9 (NGC6333)Globular ClusterOphiuchus
Messier 10 (NGC6254)Globular ClusterOphiuchus
NGC 6752Globular ClusterPavo
Messier 15 (NGC7078)Globular ClusterPegasus
Messier 34 (NGC1039)Open ClusterPerseus
Messier 46 (NGC2437)Open ClusterPuppis
Messier 47 (NGC2422)Open ClusterPuppis
Messier 93 (NGC2447)Open ClusterPuppis
Messier 71 (NGC6838)Globular ClusterSagitta
Messier 69 (NGC6637)Globular ClusterSagittarius
Messier 70 (NGC6681)Globular ClusterSagittarius
Messier 75 (NGC6864)Globular ClusterSagittarius
Messier 54 (NGC6715)Globular ClusterSagittarius
Messier 55 (NGC6809)Globular ClusterSagittarius
Messier 18 (NGC6613)Open ClusterSagittarius
Messier 21 (NGC6531)Open ClusterSagittarius
Facies, Messier 22 (NGC6656)Globular ClusterSagittarius
Messier 23 (NGC6494)Open ClusterSagittarius
Sagittarius Star Cloud (M24)Milky Way Patch Star Cloud with Open ClusterSagittarius
Messier 25Open ClusterSagittarius
Messier 28 (NGC6626)Globular ClusterSagittarius
Butterfly Cluster (M6, NGC6405)Open ClusterScorpius
Ptolemys Cluster (M7, NGC6475)Open ClusterScorpius
Messier 4 (NGC6121)Globular ClusterScorpius
Messier 80 (NGC6093)Globular ClusterScorpius
Wild Duck Cluster (M11, NGC6705)Open ClusterScutum
Messier 26 (NGC6694)Open ClusterScutum
Messier 5 (NGC 5904)Globular ClusterSerpens
HyadesOpen Star ClusterTaurus
Pleiades (M45)Open ClusterTaurus
47 TucanaeGlobular ClusterTucana

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