A reactor, also called a main reactor or reactor core, was a central power-generation device that was used in space stations and other spacefaring vehicles. The most common reactors included chemical, fission, and fusion reactors, and dated back to the Republic's earliest days. These reactors often required a variety of locally procured fuel sources, while larger starships often utilized fusion systems containing hypermatter-annihilation cores, which generated vast amounts of power. Despite this, most fuel sources were hazardous to organic beings, circulating in ship systems as corrosive liquids or combustible and poisonous gases.
The Death Star and Death Star II, planet-destroying space stations built by the Galactic Empire, both had reactor cores that, when impacted with powerful enough weapons, would explode and destroy the station.