Astrophysics (Index)About

mass-to-light ratio

(M/L, ϒ)
(measure of a population of stars or region)

The mass-to-light ratio (M/L or ϒ) is the ratio of stellar mass to stellar luminosity of a given population of stars, e.g., the population in some particular volume of space. It is often given as solar masses to solar luminosities.

In the solar neighborhood, it is about 3. The mass-to-light ratio is generally larger the smaller the star, so 3 implies lots of stars smaller than the Sun. Galaxies vary from 1 to 30: 30 for seemingly-elderly elliptical galaxies, and 1 for a galaxy with many young stars, which would include large ones. 1 does not mean the stars are generally Sun-like, but that there is sufficient luminosity from large stars to quantitatively compensate for that of the small ones.

Further reading: