Reality → Matter → Universe → Galaxies
Stars accumulate in gravitationally bound galaxies which, in turn, appear to accumulate in gravitationally bound large-scale structures of the universe. Galaxies take on various shapes: elliptical bodies, disks with spiral arms and barred centers, and irregular shapes. Genesis and evolution are largely unknown [1] .
It is estimated that our galaxy contains 200 billion stars. The number of stars in other galaxies ranges from about 10 million to 1 trillion. Galaxies accumulate in gravitationally bound groups (up to 50 galaxies), clusters (hundreds to thousands of galaxies), and superclusters (many thousands of galaxies). It is estimated that there are millions of superclusters, which apparently form still larger structures at the scale of the universe.
'Open clusters' are groups of stars within a galaxy (more than 1000 such star clusters have been discovered in the Milky Way). The pattern is formed through loose gravitational attraction and can be disturbed by close encounter with other objects. Study of the 'open clusters' gives some insight into the formation of galaxies but cannot explain the occurrence and evolution of the many observed shapes of galaxies.