<P> A quasar ( / ˈkweɪzɑːr / ) ( also known as a QSO or quasi-stellar object ) is an extremely luminous active galactic nucleus ( AGN ) . It has been theorized that most large galaxies contain a supermassive central black hole with mass ranging from millions to billions of solar masses . In quasars and other types of AGN , the black hole is surrounded by a gaseous accretion disk . As gas in the accretion disk falls toward the black hole , energy is released in the form of electromagnetic radiation . This radiation can be observed across the electromagnetic spectrum at radio , infrared , visible , ultraviolet , and X-ray , and gamma wavelengths . The power radiated by quasars is enormous : the most powerful quasars have luminosities exceeding 10 watts , thousands of times greater than an ordinary large galaxy such as the Milky Way . </P>
<P> A quasar ( / ˈkweɪzɑːr / ) ( also known as a QSO or quasi-stellar object ) is an extremely luminous active galactic nucleus ( AGN ) . It has been theorized that most large galaxies contain a supermassive central black hole with mass ranging from millions to billions of solar masses . In quasars and other types of AGN , the black hole is surrounded by a gaseous accretion disk . As gas in the accretion disk falls toward the black hole , energy is released in the form of electromagnetic radiation . This radiation can be observed across the electromagnetic spectrum at radio , infrared , visible , ultraviolet , and X-ray , and gamma wavelengths . The power radiated by quasars is enormous : the most powerful quasars have luminosities exceeding 10 watts , thousands of times greater than an ordinary large galaxy such as the Milky Way . </P>
what is at the center of a quasar
what is at the center of a quasar
a supermassive central black hole
a supermassive central black hole