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Mass-to-light ratios in application can be used to gain insight into the dark matter content and dust extinction in a galaxy. [4] 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. [5]
The relationship is represented by the equation: = where L ⊙ and M ⊙ are the luminosity and mass of the Sun and 1 < a < 6. [2] The value a = 3.5 is commonly used for main-sequence stars. [ 3 ] This equation and the usual value of a = 3.5 only applies to main-sequence stars with masses 2 M ⊙ < M < 55 M ⊙ and does not apply to red giants ...
This latter form of the relation is known as the baryonic Tully–Fisher relation (BTFR), and states that baryonic mass is proportional to velocity to the power of roughly 3.5–4. [ 8 ] The TFR can be used to estimate the distance to spiral galaxies by allowing the luminosity of a galaxy to be derived from its directly measurable line width.
A preliminary description of the three areas of this diagram was made in 2003 by Eric F. Bell et al. from the COMBO-17 survey [1] that clarified the bimodal distribution of red and blue galaxies as seen in the analysis of Sloan Digital Sky Survey data [2] and even in de Vaucouleurs's 1961 analyses of galaxy morphology.
The best-fit value of n correlates with galaxy size and luminosity, such that bigger and brighter galaxies tend to be fit with larger n. [ 5 ] [ 6 ] Setting n = 4 gives the de Vaucouleurs profile : I ( R ) ∝ e − b R 1 / 4 {\displaystyle I(R)\propto e^{-bR^{1/4}}} which is a rough approximation of ordinary elliptical galaxies .
The mass, radius, and luminosity of a star are closely interlinked, and their respective values can be approximated by three relations. First is the Stefan–Boltzmann law, which relates the luminosity L, the radius R and the surface temperature T eff. Second is the mass–luminosity relation, which relates the luminosity L and the mass M.
The observational result of Hubble's law, the proportional relationship between distance and the speed with which a galaxy is moving away from us, usually referred to as redshift, is a product of the cosmic distance ladder. Edwin Hubble observed that fainter galaxies are more redshifted. Finding the value of the Hubble constant was the result ...
Velocity dispersion (y-axis) plotted against absolute magnitude (x-axis) for a sample of elliptical galaxies, with the Faber–Jackson relation shown in blue.. The Faber–Jackson relation provided the first empirical power-law relation between the luminosity and the central stellar velocity dispersion of elliptical galaxy, and was presented by the astronomers Sandra M. Faber and Robert Earl ...