A quasar, or "quasi-stellar object," is an extremely bright and distant active galactic nucleus. They are powered by supermassive black holes at the center of galaxies, where matter falling into the black hole releases enormous amounts of energy, often outshining the entire galaxy. Quasars emit energy across a wide range of wavelengths, including radio waves, visible light, ultraviolet light, X-rays, and even gamma rays. They are among the most luminous and energetic objects in the universe.
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類星體的高解析影像，特別是哈伯太空望遠鏡，已經證明類星體是發生在星系的中心，一些類星體的宿主星系是強烈的交互作用星系或合併中的星系[3]。
