Chapter 14: Active Galaxies and Supermassive Black Holes-First called radio galaxies (283), active galaxies (283) are now known to emit energy at many wavelengths. Because the energy comes from their cores, they are known as active galactic nuclei (283).-Seyfert galaxies (283) are spirals with small, highly luminous cores and spectra that show the nuclei contain highly excited gas.-Double-lobed radio galaxies (285) emit radio energy from areas on either side of the galaxies. As described by the double-exhaust model (286), these lobes appear to be inflated by jets ejected from the nuclei of the galaxies. Where the jets push into surrounding gas, they form hot spots (286).-Jets from active galaxies are at least in part responsible for heating the gas trapped in clusters of galaxies.-The quasars (285) have a star-like appearance but very large red-shifts imply that they are very distant. To be visible at such distances, quasars must be ultra luminous. Yet rapid fluctuations in brightness show that quasars must be small.
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