An extremely powerful maser source near the nucleus of an active galaxy, which can originate from material orbiting the nucleus or from the interaction of jets from the nucleus with the surrounding interstellar medium. Megamasers can be more than a million times as powerful as maser sources within our own Galaxy. The most powerful are the OH and H₂O megamasers, which can generate more than 10³⁰ watts of radio power (enough to power 10 000 Suns).