Galaxies

Galaxies are floating apparitions of matter, dust and other phenomena in space. They are one of the biggest structures in the universe. The biggest galaxies contain up to one hundred trillion stars, whereas the smallest called dwarf galaxies contain up to a billion stars. A galaxy rotates around its center of mass. Galaxies can be divided into three divisions: elliptical, spiral and irregular.
Elliptical: These galaxies have an elliptical shape and the stars in this galaxies are distributed randomly around the center.
Spiral: They have spirals emanating from a disc.
Irregular:These have an irregular shape.
Many galaxies have black holes in their centers, around which they rotate. Galaxies can be further divided into galaxy groups, clusters and superclusters.
Galaxy Groups: These contain 50 or less gravitationally bound galaxies.
Clusters: These contain hundred to thousands of gravitationally bound galaxies.
Superclusters: These contain large groups of galaxy clusters or galaxy groups.
There are more than a 100 billion galaxies in space, each containing up to a billion stars each.