Star clusters

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Lupe Rioné, Amateur astronomer (Spain)

Our star, the Sun, was formed about 4.57 billion years ago. It belongs to the spectral class G2, known as a yellow dwarf, a medium-sized star. At the center of the solar system, the Sun keeps numerous planets, comets, and meteors orbiting around it thanks to its gravitational force. Similarly, there are numerous solar systems that house planets. Likewise, stars can group into small or immense clusters of up to millions of stars. These groups are called open or globular star clusters, according to their characteristics.

Open clusters

Also called galactic clusters, because they are found within the galaxy, open clusters are groups of only tens or hundreds of young stars formed from the same nebula. They have a random, usually asymmetric, structure, and their stars are gravitationally bound to each other. Using a moderate telescope, many of the cluster-forming stars may be individually observed, such as the case of the well-known  Pleiades or M45, one of the most amazing star clusters in the sky. 

Pleiades or M45. Credit: Jaume Zapata

Globular clusters

Globular clusters are concentrations of thousands to millions of stars that are gravitationally bound. These objects are usually found in the galactic halo orbiting the host galaxy, but they can also be found in the center of the Milky Way.

Unlike open clusters, globular clusters are home to ancient stars whose ages can reach 13 billion years. In other words, they contain stars that were formed in the early universe. Therefore, they offer information about galactic and stellar evolution. Most of their stars are low-mass red dwarfs and medium-mass yellow stars, and it is estimated that they are regions where no star formation takes place. The density of these clusters is responsible for their spherical and compact structure. There are about 150 known globular clusters in our Milky Way, but our neighbor, the Andromeda Galaxy, is estimated to contain about 500. 

M13 – Globular cluster. Credit: NASA.

Somewhere, something incredible is waiting to be known

Carl Sagan 

M10 – Globular Cluster | Cúmulo Globular

M10 is a very bright and star-rich cluster. Located in the constellation Ofiuco, it is estimated to be approximately 16,000 light-years from the center of our galaxy. An analysis of its radial velocity allows us to deduce that it is moving away from Earth at more than 271,440 km/h.

M9 – Globular Cluster | Cúmulo Globular

Like all globular clusters, M9 is a spectacle in itself, and one of the oldest and most intriguing objects in our galaxy. M9 stands out as one of the closest globular clusters to the center of our galaxy, only 5,500 light-years away.

M8 – Lagoon Nebula | Nebulosa de la Laguna

Like all emission nebulae, M8 or NGC 6523 is a gigantic HII region, that is, a spectacular cradle of stars. With a magnitude of 5.8, this incredible nebula boasts many large, hot stars, whose ultraviolet radiation sculpts the gases and cosmic dust, giving it its characteristic shape.

M7 – Open Cluster | Cúmulo Abierto

Also known as NGC 6475, M7 is an open cluster, that is, a group of gravitationally bound stars formed by the same molecular cloud. It is a very sparse cluster, located in a very rich region of the Milky Way.

M6 – Open Cluster | Cúmulo Abierto

This beautiful cluster comprises more than 200 stars and has a diameter of about 12-20 light-years. It is estimated that its stars were formed about 100 million years ago, which means that while dinosaurs roamed the planet, M6 was just beginning to shine in the sky.

M5 – Globular Cluster | Cúmulo Globular

The globular cluster M5 is probably one of the most interesting because it is one of the oldest, largest, and brightest clusters. It is located in the constellation of The Serpent (Serpens) at a distance of approximately 24,500 light-years.

M4 – Globular Cluster | Cúmulo Globular

Also called NGC 6121, M4 is the closest globular cluster to the Earth. M4 contains about 100,000 stars, and like most globular clusters, it is a very old structure, about 12-13 billion years old.

M3 – Globular Cluster | Cúmulo Globular

M3, also called NGC 5272, is one of the largest and most spectacular clusters that we can observe in our galaxy. In fact, M3 was the first original discovery by Charles Messier.

M2 – Globular Cluster | Cúmulo Globular

M2 is a globular star cluster and the second object in the Messier catalog. Also called NGC 7089, it was discovered in 1746 by French astronomer Jean-Dominique Maraldi.

M1 – Crab Nebula | Nebulosa del Cangrejo

M1 is the remnant of a supernova explosion that was observed by Chinese astronomers during the Song Dynasty in the 11th century.
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