mass-to-light ratio

The mass-to-light ratio (M/L or ϒ, the Greek letter upsilon) 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. The value is often given as solar masses to solar luminosities, i.e., scaled so the Sun's M/L is 1. The solar neighborhood value is about 3. The ratio is generally larger the smaller the star, and 3 implies numerous stars smaller than the Sun. Galaxies vary from 1 to 30: 30 for apparently-elderly elliptical galaxies, and 1 for a galaxy with many young stars, which would include large ones. A ratio of 1 does not imply most of a galaxy's stars are Sun-like: more likely it is the result of having enough stars larger than the Sun to balance all the small stars.