mass-luminosity relation

(M-L relation) An approximate relation between the mass and luminosity of main-sequence stars, predicted by Eddington in 1924. Although having some basis in theory it is obtained empirically from a graph of absolute bolometric magnitude against the logarithm of mass (in solar units), i.e. M /M _O, for a large number of binary stars. Most points lie on an approximately straight line. Since a star's absolute bolometric magnitude is a function of the logarithm of its luminosity (in solar units), i.e. L /L _O, this line is represented by the M-L relation:

log(L /L _O) = n log(M /M _O )

L /L _O = (M /M _O )ⁿ

n averages about 3 for bright massive stars, about 4 for Sun-type stars, and about 2.5 for dim red dwarfs of low mass. The relation holds for main-sequence stars, which all have a similar chemical composition and have similar internal structures and nuclear power sources. It is not obeyed by white dwarfs (degenerate matter) or red giants (extended atmospheres).

Collins Dictionary of Astronomy © Market House Books Ltd, 2006

mass-luminosity relation

[′mas ‚lü·mə′näs·əd·ē ri‚lā·shən]

(astrophysics)

A relation between stellar magnitudes and mass of the stars; when the absolute magnitudes of stars are plotted versus the logarithms of their masses, the points fall closely along a smooth curve.

The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Mass-Luminosity Relation

in astronomy, the relation, deduced from observations of binary stars, between the mass and the luminosity of a star. Such a relation was theoretically predicted by the British astronomer A. Eddington in the early 20th century. In practice, all types of stars, except white dwarfs, conform to the empirically found law. However, the parameters of the relation between the star’s bolometric luminosity L_b and mass m

L_b = kmⁿ

may differ significantly for different groups of stars. Thus, according to the most complete data available by the early 1970’s, k = 0.1 and n = 1.5 for faint stars with bolometric stellar magnitudes M_b of less than 7.5. For brighter stars, up to a bolometric stellar magnitude of M_b = -0.3, k ≈ 1 and n = 4.0.

The mass-luminosity relation, extended to include stars that are not members of binary systems, permits the masses of stars to be estimated from the observationally evaluated luminosities of the stars.

REFERENCE

Martynov, D. Ia. Kurs obshchei astrofiziki. Moscow, 1965.