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Image: Quasar Pair Captured in Galaxy Collision. Credits: X-ray: NASA/CXC/SAO/P. Green et al. Optical: Carnegie Obs./Magellan/W. Baade Telescope/J.S. Mulchaey et al. Strong observational evidence suggests that every massive galaxy hosts a supermassive black hole in its nucleus. The central black hole (BH) is an important component of the galaxy, since the BH mass is correlated with the global properties of the host galaxy, e.g., dispersion velocity, bulge luminosity, or bulge mass.

Image: Colour composite image of Centaurus A, revealing the lobes and jets emanating from the active galaxy’s central black hole. This is a composite of images obtained with three instruments, operating at very different wavelengths. The 870-micron submillimetre data, from LABOCA on APEX, are shown in orange. X-ray data from the Chandra X-ray Observatory are shown in blue. Visible light data from the Wide Field Imager (WFI) on the MPG/ESO 2.2 m telescope located at La Silla, Chile, show the background stars and the galaxy’s characteristic dust lane in close to "true colour". Credit: ESO/WFI (Optical); MPIfR/ESO/APEX/A.Weiss et al. (Submillimetre); NASA/CXC/CfA/R.Kraft et al. (X-ray) A maser, an acronym for 'microwave amplification by stimulated emission of radiation', is a device that produces coherent electromagnetic waves through amplification by stimulated emission. The maser was the forerunner of the laser: they work by the same principle. The difference is...

Image Credit: NASA/Goddard Space Flight Center Radio emission of radio-quiet quasars may be due to stars formation in the quasar host galaxy, to a jet launched by the supermassive black hole, or to relativistic particles accelerated in a wide-angle radiatively-driven outflow.

Credit: NASA/ESA Recently it has been suggested that quasars can be primarily responsible for the reionization of the universe.