An active galaxy is a type of galaxy that emits an unusually high amount of energy, often in the form of light, radio waves, or X-rays. This energy is typically produced by a supermassive black hole at the galaxy's center, which pulls in surrounding gas and dust. As this material spirals into the black hole, it heats up and emits radiation, making the galaxy appear much brighter than normal. There are different types of active galaxies, including quasars, blazars, and Seyfert galaxies. Each type has unique characteristics based on the orientation of the black hole and the surrounding material. Active galaxies are important for understanding the evolution of galaxies and the role of black holes in the universe.