ABSTRACT
4.1 Overview
Objects which emit light, whether they are cigars, lightbulbs, stars or galaxies can be characterized by their emitted energy per unit mass. This is parameterized as the mass-to-luminosity ratio (M/L). For cosmological purposes, it is most convenient to express M/L in terms of solar masses and luminosities. For main sequence stars it can be shown that L ∝ Mn where n ≈ 3.5–4. Thus a 10M⊙ star has M/L ≈ 10-3, an M⊙ star has M/L = 1 and a 0.1M⊙ star has M/L ≈ 1000. The term dark matter refers to the the existence of objects which have extreme M/L. Identifying the nature and extent of the dark matter component in the Universe is arguably the most significant unsolved problem in all of cosmology.
