Generally, the stars live alone and remain in a cluster. The star group is of two types: open and round.
Open star group
These are sometimes called galaxial star clusters because these star clusters are close to us with a comparative point of view and they are in our galaxy milky way itself. In the open star, there can be some dozen stars and some hundred stars. It is believed that all these stars are created from the same nebula and keep the same relative motion. For this reason, the stars of a group are spreading in different directions, and the star group is scattered. These star groups can also be destroyed, but it can happen only when a large star passes through the star group and with its gravitational power, affect the speed of stars.
In some star groups, some stars appear more rather than the rest of the stars, it can also be from the brightness or position of that star. The star shown in the picture is “Pleiades Constellation“, which is called “Seven Sisters” or Pleiades in the West. This star group is known from prehistoric times (700-1000 BC). It is called M45 in scientific term, it is approximately 440 light years away. The 7 stars of this star show with the naked eyes but its 14 stars can be seen from the telescope. But this is the brightest star of this star group, in reality this star has more than 500 stars.
In a new open star, there is a residual substance of its maternal nebula in between the stars. Which is slowly destroyed due to the radiation of stars, gravity. But in the case of Pleiades, it is not so, the material that appears in the middle of this star group is another Nebula.
Globular Star Cluster
These star clusters are quite different from the open star group. Our galaxy is not such a star group in the center of the galaxy, all the circular star clusters are in the outer part of our galaxy. Milky Way has 150 known circular star clusters. Other galaxies may have circular star clusters, but not necessarily. The Andromeda Galaxy (M31) has thousands of star clusters. While the Dwarf galaxy Sagittarius does not have any circular star group.
According to the name, the circular star group is round like a ball while the open star group is in the shape of the mother nebula. There can be thousands of stars, millions of stars in the circular star group.
The circular star group is one of the first masses created at the time of creation of the universe, and it is still after a thousand years. The circular star group of our galaxy is at least 11.3 billion years old. It also helps us to know the age of the universe. The age of the universe can not be less than the age of a star.
Most circular star clusters are in the shape of a giant ball made of taro, but there is a difference in their size. If our sun was part of a circular circular group then night would never happen!