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Luminous Infrared Galaxies or (LIRG's) are galaxies with luminosities, the measurement of brightness, above . LIRG's are more abundant than starburst galaxies, Seyfert galaxies and quasi-stellar objects at comparable luminosity. Infrared galaxies emit more energy in the infrared than at all other wavelengths combined. A LIRG's luminosity is 100 billion times that of our sun. Galaxies with luminosities above , are Ultra-Luminous Infrared Galaxies (ULIRG's). Many of the LIRG's and ULIRG's are showing interactions and disruptions. Many of these type of galaxies spawn about 100 new stars a year as compared to ours which spawn one a year, this creates the high level of luminosity. More luminous than ULIRGs are the HLIRG, Hyper-Luminous Infrared Galaxies. The most luminous class are the ELIRG, Extremely Luminous Infrared Galaxies. == Origin and Evolution of LIRG's == Infrared galaxies appear to be single, gas rich spirals whose infrared luminosity is created largely by the formation of stars within them. However some galaxies' luminosity come from an Active Galactic Nucleus or AGN. These AGNs reside in compact regions at the centres of galaxies and have higher than normal luminosity. The emission of the AGN has been observed in the radio, infrared, optical, ultra-violet, X-ray and gamma ray wavebands. These types of galaxies were discovered in 1983 with IRAS. In some cases an LIRG's luminosity may come from starburst, the creation of stars, and also an active galactic nucleus. These galaxies contain more energy in the infrared portion of the spectrum, not visible to the naked eye. The energy given off by LIRG's is comparable to that of a quasar, which before was known as the most energetic object in the universe. The reason that we are not able to see the optical light from these galaxies is because they are gas rich, meaning that gases within the galaxy absorb most of the light and re-emit it in the infrared. A large fraction of galaxies in the universe with extreme luminosities such as LIRG's are known to have an active black hole. LIRG's are known to live in denser parts of the universe than non-LIRG's. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Luminous infrared galaxy」の詳細全文を読む スポンサード リンク
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