Deepsky-objects has been grouped by their character, these groups are open clusters, globular clusters, planetary nebulae, supernova remnants, bright nebulae, dark nebulae and galaxies. Galaxy Galaxy is a system of stars, dust, and gas held together by gravity. Galaxies are scattered throughout the universe. They range in diameter from a few thousand to half a million light-years. Large galaxies have more than a trillion stars.
Small galaxies have fewer than a billion.
Astronomers have photographed millions of galaxies through telescopes. They estimate that there are about 100 billion galaxies in the universe. Galaxies are distributed unevenly in space. Some galaxies are found alone in space, but most are grouped in formations called clusters. Clusters of galaxies range in size from a few dozen members to several thousand.