The Most Massive Globular star cluster "Omega Centauri or NGC 5139"

We all must have heard about star clusters. A group of stars is known as a cluster. Clusters can be of two types open cluster, and globular cluster. Some time ago a planet named Methuselah was considered to be the oldest planet in the universe. In fact, the planet was also found as a globularcluster. Omega Centauri is located at a distance of 17,090 light years from us. This cluster is the most massive cluster ever discovered. In a globular cluster, stars are very close to each other and are tightly bound by Gravity. 

All the stars revolve around the galactic core. But Omega Centauri is considered to be the most massive cluster ever. It is estimated to have more than 10 million stars in it. This cluster is so large that its diameter is about 150 light years. It is also known as NGC 5139 or Cald well 80. This is the largest massive cluster ever discovered in the Milky Way galaxy. This cluster can be easily seen from the earth with the naked eyes. 

All the stars in it are only 0.1 light years away from each other. Due to the large number of stars and their short distance from each other, this cluster looks very bright. Omega Centauri has long been considered the only star. It is the first mentioned by Ptolemy In 150 AD.  He recorded it as a star on the horse's back.  Then in 1603 Johann Bayer Named the object Omega Centauri using Ptolemy’s figures. It is not yet known if Omega Centauri is actually a star cluster, not a single star. It was then studied in depth by Edmond Halley in 1677 and listed as the first non-Stellar object.

The object was a discovered to be a globular cluster by the Scottish astronomer James Dunlop in 1826.  This is how it turns out to be a cluster from a single star. This cluster is a very large structure. The number of the star near its Centre is a very large. The total mass of this cluster is estimated to be equal to about 4 million solar messes.  It contains very old stars. These stars are called Population II Stars. These stars are also known as metal poor stars.  Population II type stars are the oldest stars in the universe, mostly found in a globular cluster.

This category includes stars that formed 10 billion to 13 billion years ago. These stars, formed after the big bang, contain a large amount of hydrogen and helium. But the population II stars contain very small amount of heavy metals called oxygen, silicon, neon and iron called Alpha elements.  The number of such stars in the Omega Centauri is very high.  In depth study has a shown that orbital velocity of such stars is much higher than that of other stars.  In addition, the population I type stars include young stars that form from 1 million year to a few billion years ago.

Unlike population II, these stars contain a large amount of Alpha elements. In the Stellar population stars are classified in Astronomy based on their different age generations.  This cluster is thought to be a Core of a destroyed Galaxy. This may have been later absorbed by the Milky Way galaxy. The cluster currently discovered by scientists is the brightest and most massive giant star cluster. Scientists believe that the cluster is a remnant of a pre-existing small Galaxy.

This must have happened a long time ago.  it is generally observed that stars in other clusters are about the same age and have the same chemical composition. But apart from that, the stars in Omega Centauri are quite different.  The chemistry of the stars in it has also been found to be different to it and there are huge difference in the age of the stars. It also has very young stars and very old stars. Scientists are trying to understand why this is a so. Observations made a few years ago have shown that there is a very massive object at the centre of this globular cluster.

To find out what could have happened, scientists observed it with the Hubble Space Telescope and Gemini observatory. Data from  Hubble's advanced camera for surveys show that  stars near the centre of the cluster are orbiting at  it very high speed around its Core. Astronomers try to measure the speed and brightness of stars near the centre. The Scientist says it has an intermediate- mass black hole at its centre. When the mass of the black hole at its centre was calculated, its mass was estimated to be equal to 40,000 solar masses.

This giant black hole is much larger than the stellar mass black hole. But it is much smaller than the supermassive black hole in the centre of a galaxy. At the moment this cluster is a 10 times more massive than any globular cluster. No planets are usually found in such clusters. The gravity of the stars in the cluster does not allow a planet to form. Perhaps this is why planets do not exist in such clusters. There is only room for the stars. As a black hole is found in it centre, it can be assumed that the Omega Centauri must have been a dwarf Galaxy before. Whatever it is for us there are so many more interesting galactic object scattered in every direction to amaze us in this universe.