astrophysics Astrophysics is a science that employs the methods and principles of physics and chemistry in the study of astronomical objects and phenomena. As one of the founders of the discipline, James Keeler, said, astrophysics "seeks to ascertain the ...

and

physical cosmology Physical cosmology is a branch of cosmology concerned with the study of cosmological models. A cosmological model, or simply cosmology, provides a description of the largest-scale structures and dynamics of the universe and allows study of fu ...

the mass-to-light ratio, normally designated with the Greek letter

upsilon Upsilon (, ; uppercase Υ, lowercase υ; ''ýpsilon'' ) or ypsilon is the twentieth letter of the Greek alphabet. In the system of Greek numerals, has a value of 400. It is derived from the phoenician alphabet, Phoenician Waw (letter), waw ...

, , is the quotient between the total

mass Mass is an Intrinsic and extrinsic properties, intrinsic property of a physical body, body. It was traditionally believed to be related to the physical quantity, quantity of matter in a body, until the discovery of the atom and particle physi ...

of a spatial volume (typically on the scales of a

galaxy A galaxy is a Physical system, system of stars, stellar remnants, interstellar medium, interstellar gas, cosmic dust, dust, and dark matter bound together by gravity. The word is derived from the Ancient Greek, Greek ' (), literally 'milky', ...

or a cluster) and its

luminosity Luminosity is an absolute measure of radiated electromagnetic radiation, electromagnetic energy per unit time, and is synonymous with the radiant power emitted by a light-emitting object. In astronomy, luminosity is the total amount of electroma ...

. These ratios are calculated relative to the

Sun The Sun is the star at the centre of the Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light a ...

as a baseline ratio which is a constant = 5133 kg/ W: equal to the

solar mass The solar mass () is a frequently used unit of mass in astronomy, equal to approximately . It is approximately equal to the mass of the Sun. It is often used to indicate the masses of other stars, as well as stellar clusters, nebulae, galaxie ...

divided by the

solar luminosity The solar luminosity () is a unit of radiant flux (Power (physics), power emitted in the form of photons) conventionally used by astronomers to measure the luminosity of stars, galaxy, galaxies and other celestial objects in terms of the output of ...

, . The mass-to-light ratios of galaxies and clusters are all much greater than due in part to the fact that most of the

matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be touched are ultimately composed of atoms, which are made up of interacting subatomic pa ...

in these objects does not reside within stars and observations suggest that a large fraction is present in the form of

dark matter In astronomy, dark matter is an invisible and hypothetical form of matter that does not interact with light or other electromagnetic radiation. Dark matter is implied by gravity, gravitational effects that cannot be explained by general relat ...

. Luminosities are obtained from photometric observations, correcting the observed

brightness Brightness is an attribute of visual perception in which a source appears to be radiating/reflecting light. In other words, brightness is the perception dictated by the luminance of a visual target. The perception is not linear to luminance, and ...

of the object for the distance dimming and

extinction Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

effects. In general, unless a complete

spectrum A spectrum (: spectra or spectrums) is a set of related ideas, objects, or properties whose features overlap such that they blend to form a continuum. The word ''spectrum'' was first used scientifically in optics to describe the rainbow of co ...

of the

radiation In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or a material medium. This includes: * ''electromagnetic radiation'' consisting of photons, such as radio waves, microwaves, infr ...

emitted by the object is obtained, a model must be extrapolated through either

power law In statistics, a power law is a Function (mathematics), functional relationship between two quantities, where a Relative change and difference, relative change in one quantity results in a relative change in the other quantity proportional to the ...

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 lens A gravitational lens is matter, such as a galaxy cluster, cluster of galaxies or a point particle, that bends light from a distant source as it travels toward an observer. The amount of gravitational lensing is described by Albert Einstein's Ge ...

ing. Masses can also be measured through CMB backlighting. Typical mass-to-light ratios for galaxies range from 2 to 10 while on the largest scales, the mass to light ratio of the

observable universe The observable universe is a Ball (mathematics), spherical region of the universe consisting of all matter that can be observation, observed from Earth; the electromagnetic radiation from these astronomical object, objects has had time to reach t ...

is approximately 100 , in concordance with the current best fit cosmological model. Mass-to-light ratios in application can be used to gain insight into the dark matter content and dust extinction in a galaxy. Historically, rotation curves for spiral galaxies have been used to study galaxies, but mass-to-light ratios prove more accurate as a method of measuring mass.

References

External links

* {{cite web, last=Merrifield, first=Michael, title=''ϒ'' – Mass to Light Ratio, url=http://www.sixtysymbols.com/videos/masstolight.htm, work=Sixty Symbols, publisher= Brady Haran for the

University of Nottingham The University of Nottingham is a public research university in Nottingham, England. It was founded as University College Nottingham in 1881, and was granted a royal charter in 1948. Nottingham's main campus (University Park Campus, Nottingh ...

, year=2009 Concepts in astrophysics Physical cosmology Ratios

See also

References

External links