Galaxy

A galaxy is a gravitationally bound system of stars, stellar remnants, interstellar gas, dust, and dark matter. The word "galaxy" derives from the Greek term galaxias, meaning "milky," a reference to our own galaxy, the Milky Way. In Hebrew, the word for galaxy is גלקסיה (galaksia), while in Spanish it is galaxia, in French galaxie, and in German Galaxie. Galaxies range in size from dwarfs with just a few hundred million stars to giants with one hundred trillion stars, each orbiting its galaxy's center of mass. Galaxies are categorized according to their visual morphology, including elliptical, spiral, and irregular. They are the fundamental building blocks of the universe, with the largest and most massive ones often found at the center of galaxy clusters. The study of galaxies and their distribution in space is known as cosmology, a branch of astronomy that seeks to understand the origin and evolution of the universe.