20 Years of Hubble Science: Exoplanets

A galaxy is a vast and complex system that consists of stars, star clusters, interstellar gas, dust, and dark matter, all bound together by gravity. Galaxies come in a variety of shapes, sizes, and compositions, and they are the fundamental building blocks of the universe. They can range in size from dwarf galaxies with just a few billion stars to massive galaxies containing trillions of stars.

The Milky Way, for instance, is the spiral galaxy that contains our solar system and is home to billions of stars, including our Sun. Other types of galaxies include elliptical galaxies, which are often more rounded and lack the distinctive spiral arms, and irregular galaxies, which have irregular shapes and structures.

Galaxies are not uniformly distributed throughout the universe but are instead found in groups called galaxy clusters, which are collections of galaxies bound together by gravity, and in even larger structures known as superclusters. The study of galaxies and their properties provides valuable insights into the formation, evolution, and dynamics of the universe as a whole.