m2 – globular cluster

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Lupe Rioné, Amateur astronomer (Spain)

Type

Globular cluster

Location

Constellation of Aquarius

Distance

37,000 light-years

Size

175 light-years

Globular clusters: Globular clusters are concentrations of thousands to millions of stars joined gravitationally. They all orbit in the halo of a galaxy, although some of them can be located near the center of the Milky Way.

Do you want to know more about stellar clusters?

History and discovery

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, while he was observing a comet. Because many astronomers were “comet hunters” at the time, a wide variety of other celestial bodies such as galaxies, nebulae, and star clusters were discovered. At the time, Maraldi described M2 as a very round nebula.

14 years later, in 1760, Charles Messier observed it on his own. Studying it again in 1764, he described it in his catalog as a nebula, because its structure was not easily distinguishable. However, in 1783 William Herschel detailed M2 much more precisely, and in a very approximate way to how we know it today. Herschel wrote: “The scattered stars were seen with a well-defined focus, in which it seems that the condensed central light is due to the multitude of stars that appeared at various distances behind and close to each other”.

This spectacular composite image of visible and infrared light taken by the Hubble Space Telescope shows the dense core of M2. Credit: Hubble

M2 – Globular Star Cluster. Credits NASA

Location and observation

M2 is located in the constellation of Aquarius, forming a triangle with the stars Alpha and Beta of that constellation. Its localization is easy and can be distinguished as the end of a row of stars. The cluster can be seen from both the northern and southern hemispheres with an apparent magnitude of 6.5. However, without excellent visibility conditions, it is not easy to observe with the naked eye. With the help of a small telescope or binoculars, M2 would be seen as a single object, while with a powerful telescope we can see the stars that make up this beautiful cluster.

Widefield photo where we can see the beautiful M2 Cluster . Credit: Oservatori de la Pobla Torna (OPT)

M2 star cluster. Credit: iniciacion.com

Characteristics 

M2 is one of the most exciting objects to observe. Because globular clusters are ancient structures, these celestial bodies provide professional astronomers with clues about galactic evolution. Located 37,000 light-years away in the galactic halo, and with about 150,000 stars, its Halton Arp color-magnitude diagram (1962) estimated the age of its stars to be between 11 and 13 billion years. That is, they are very old stars that were formed during the dark age of the universe. The structure of the cluster is spherical with a dense, compact core about 3.7 light-years in diameter, while the entire cluster extends about 175 light-years. In the density scale, M2 is the second largest with 12° degrees of density.

The brightest stars in M2 are red and yellow giants, with a magnitude of 16.1, while the stars in its horizontal branch have a brightness of 13.6. The cluster has about 21 variable stars, the first two discovered by Bailey in 1895. Most of them belong to the variable star type RR Lyrae (named after its prototype which is RR de la Lyra). They are variable stars of spectral types A and F. A particularity of this cluster is that it contains a variable star of type RV Tauri (named after RV tau, the variable star in the constellation of Taurus), a type of supergiant variable star. These two types of variable stars show changes in luminosity linked to radial pulsations on their surface, which are accompanied by changes in the spectral type. For this reason, when these stars are at their maximum brightness they can give a different appearance to the cluster. Really fascinating.

M2 – Globular star cluster. Credit: NASA

M2 can be located in the constellation of Aquarius 

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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