Final answer:
The unusually luminous centers of some galaxies are powered by accretion onto supermassive black holes, which obtain fuel from the interstellar matter in the galaxy. This process can be observed in quasars and other active galaxies that have jets of energetic particles extending beyond the limits of the parent galaxy.
Step-by-step explanation:
The unusually luminous centers of some galaxies are powered by accretion onto supermassive black holes. Galaxies start out with large amounts of interstellar gas and dust, which can be gradually converted into stars as the galaxy evolves. Any interstellar matter that ventures too close to the black hole may be accreted by it, providing it with fuel and energy. This process can be observed in quasars and other active galaxies that have jets of energetic particles extending beyond the limits of the parent galaxy.