m4 – globular cluster


Lupe Rioné, Amateur astronomer (Spain)


Globular cluster


Constellation of Scorpion 


7,200 light-years


75 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.

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Discovery and Location

Also called NGC 6121, M4 is the closest globular cluster to the Earth. It was discovered by Swiss astronomer Jean Philippe Loys de Cheseaux in 1746 in the constellation of Scorpion, near the brightest star in this region of the sky: Antares. Later, in 1764, Charles Messier included it in his catalog as M4. This was the first cluster that Messier “solved”, observing its true nature as a collection of tens of thousands of stars. With a magnitude of +5.6 this celestial body can be seen with the naked eye on a very dark night. With small telescopes of moderate aperture, we can see its spectacular shape.

Image of M4 from the El Querol Observatory (Tarragona). skywatcher 200/1000 reflecting telescope

M4 cluster. Credit: Hubble/NASA


M4 contains about 100,000 stars, and like most globular clusters, it is a very old structure, about 12-13 billion years old. If we consider that the first stars formed about 1 billion years after the Big Bang, it can be seen that it is useful to determine the age of the universe and to study its evolution. In addition, it contains 43 variable stars and also quite a few white dwarfs, so it has a good number of the oldest stars in the Milky Way.

A white dwarf is the result of a red giant star that as it ages expels its outer layers into interstellar space .

Its structure is very disordered (or open) and its central mass is relatively small compared to other clusters. The central mass has a diameter of 8 light years, but its gravitational influence, or the stars linked to the cluster, is 140 light years.

Spectacular image of the star Antares and  M4. Credit: Randy Carter

Artistic recreation of the planet Gemini orbiting the binary system in M4. Credit: NASA

Pulsar in M4

In 1987 the PSR B1620-26 pulsar was discovered in M4, being the first object of this type discovered in a globular cluster. This pulsar is located on the outskirts of the central region of the cluster and has a period of 3 milliseconds, that is, it turns on its axis every 3 thousandths of a second, 10 times faster than the central pulsar of the Crab Nebula.

A pulsar is a rapidly rotating neutron star with an intense magnetic field, inclined with respect to its axis of rotation.

Image taken from the El Querol observatory in Tarragona where we can see the constellation of Scorpion where the globular Cumulus M4 and the Antares Star are located.

Later, it was discovered that PRS B1620-20 was part of a binary system accompanied by a white dwarf. In addition, in 2003 a giant planet between 3 and 10 times the mass of Jupiter was discovered orbiting this binary system. The planet is known as Gemini or Methuselah, due to its age which is estimated at 12 billion years.

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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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