sample.short - Unknown Astronomy Major (Draft received a...

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Unknown Astronomy Major (Draft received a grade of B) Active Galactic Nuclei A fascinating area of study in astronomy involves extremely small, compact nuclei of galaxies that emit extremely large amounts of radiation. These Active Galactic Nuclei, usually referred to as AGNs, have several basic characteristics. AGNs have unusually high luminosities, with a large contrast between the brightness of the nucleus and large-scale structures. The continuum emission of AGNs is nonthermal in origin, with more flux in the ultraviolet, infrared, radio, and x-ray regions of the electromagnetic spectrum than is found in normal galaxies. They contain a small region of at most a few lightyears across which undergoes rapid variability. AGNs often appear explosive or have jet-like protuberances. Finally, they often have broad emission lines. Although the basic types of Active Galactic Nuclei each have slightly different characteristics, astronomers believe that all AGNs are fueled by accretion of matter onto a supermassive black hole. Seyfert galaxies, which are usually spiral galaxies, are characterized by lower luminosity, quasar-like nuclei, with the host galaxy clearly detectable. (Quasars, originally termed quasi-stellar objects, are intense, point-like sources of electromagnetic radiation.) Their nuclei are characterized by a high surface brightness. There are two subclasses of Seyferts: Type 1 and Type 2. Type 1 Seyferts have two sets of emission lines superimposed on each other. The first is characteristic of low-density ionized gas ( -3 6 3 cm 10 10 ! " e n ) and has widths on the order of several hundred kilometers per second, which is broader than the emission lines in normal galaxies. These are the
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This note was uploaded on 06/13/2011 for the course PHYSICS 596 taught by Professor Staff during the Fall '08 term at Ohio State.

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sample.short - Unknown Astronomy Major (Draft received a...

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