Star

Stars were immensely massive celestial bodies that underwent natural, self sustaining nuclear fusion. Due to the nature of this process, stars produced huge amounts of energy in the form of radiation, heat and light. Stars were much more massive than smaller bodies such as planets, and tended to be composed primarily of hydrogen and helium. The immense gravity of stars often caused the aforementioned planets (among other bodies) to orbit around them, a star with one or multiple orbiting planets giving rise to a star system.

Classification
Stars were classified as standards (also main sequence), giants or dwarfs based on their evolution.