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翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク Mass-to-light ratio ： ウィキペディア英語版 Mass-to-light ratio In astrophysics and physical cosmology the mass to light ratio, normally designated with the symbol $\backslash Upsilon$〔Mihalas and McRae (1968), ''Galactic Astronomy'' (W. H. Freeman)〕 is the quotient between the total mass of a spatial volume (typically on the scales of a galaxy or a cluster) and its luminosity. These ratios are often reported using the value calculated for the Sun as a baseline ratio which is a constant $\backslash Upsilon\_\backslash odot$ = 5133 kg/W equal to a solar mass () divided by a solar luminosity (), (/). The mass to light ratios of galaxies and clusters are all much greater than $\backslash Upsilon\_\backslash odot$ due in part to the fact that most of the matter in these objects does not reside within stars and observations suggest that a large fraction is present in the form of dark matter. Luminosities are obtained from photometric observations, correcting the observed brightness of the object for the distance dimming and extinction effects. In general, unless a complete spectrum of the radiation emitted by the object is obtained, a model must be extrapolated through either power law or blackbody fits. The luminosity thus obtained is known as the bolometric luminosity. Masses are often calculated from the dynamics of the virialized system or from gravitational lensing. Typical mass to light ratios for galaxies range from 2 to 10 $\backslash Upsilon\_\backslash odot$ while on the largest scales, the mass to light ratio of the observable universe is approximately 100 $\backslash Upsilon\_\backslash odot$, in concordance with the current best fit cosmological model. ==References== 〔 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「Mass-to-light ratio」の詳細全文を読む スポンサード リンク 翻訳と辞書 : 翻訳のためのインターネットリソース Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.