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| In [[astrophysics]] and [[physical cosmology]] the '''mass to light ratio''', normally designated with the symbol <math>\Upsilon</math><ref>Mihalas and McRae (1968), ''Galactic Astronomy'' (W. H. Freeman)</ref> is the quotient between the total [[mass]] of a [[spatial volume]] (typically on the scales of a [[galaxy]] or a [[galaxy cluster|cluster]]) and its [[luminosity]]. These ratios are often reported using the value calculated for the [[Sun]] as a baseline ratio which is a constant <math>\Upsilon_\odot</math> = 5133 [[kilogram|kg]]/[[Watt|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 <math>\Upsilon_\odot</math> 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]].
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| Luminosities are obtained from [[photometry (astronomy)|photometric]] observations, correcting the observed [[brightness]] of the object for the [[cosmic distance ladder|distance dimming]] and [[interstellar extinction|extinction]] effects. In general, unless a complete [[electromagnetic spectrum|spectrum]] of the [[Electromagnetic radiation|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]].
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| Masses are often calculated from the dynamics of the [[virial theorem|virialized system]] or from [[gravitational lens]]ing.
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| Typical mass to light ratios for galaxies range from 2 to 10 <math>\Upsilon_\odot</math> while on the largest scales, the mass to light ratio of the [[observable universe]] is approximately 100 <math>\Upsilon_\odot</math>, in concordance with the [[Lambda-CDM model|current best fit cosmological model]].
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| ==References==
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| <references />
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| ==External links==
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| * {{cite web|last=Merrifield|first=Michael|title=γ – Mass to Light Ratio|url=http://www.sixtysymbols.com/videos/masstolight.htm|work=Sixty Symbols|publisher=[[Brady Haran]] for the [[University of Nottingham]]|year=2009}}
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| [[Category:Physical cosmology]]
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| [[Category:Astrophysics]]
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| {{astronomy-stub}}
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Latest revision as of 05:07, 24 November 2014
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