An accretion disk is a structure formed by diffuse material in orbital motion around a massive central body. Friction and other forces cause the material to spiral inward, releasing immense potential energy as heat and light, often becoming the brightest objects in the universe.
efficiency. The Milky Way is a barred spiral galaxy containing 100–400 billion stars. At its center lies Sagittarius A*, a supermassive black hole around which the entire galaxy rotates.