Luminositeter

Luminositeter, plural of luminositet, are a measure of the intrinsic power output of astronomical objects, i.e., the total energy they emit per unit time across all wavelengths. They are usually expressed in watts or in solar luminositeter, with 1 solar luminositet L⊙ equal to about 3.828 × 10^26 W. In astronomy, several related quantities are used for different purposes: bolometrisk luminositet (total across all wavelengths), spektral luminositet Lν (per unit frequency) or Lλ (per unit wavelength), and band- eller driftsluminositet obtained by integrating over a specific wavelength range or filter.

The fundamental relation between luminositeter and observed flux is L = 4π d^2 F for isotropic emitters, where d is the distance to the source and F is the observed flux. In cosmology, the analogous relation involves the luminosity distance dL, with F = L / (4π dL^2). For extended objects like stars, the bolometric luminositet is linked to intrinsic parameters via L = 4π R^2 σ T_eff^4, tying luminositet to radius and effective temperature through the Stefan-Boltzmann law.

Units and magnitudes: astronomers often express luminositeter relative to the Sun, and use bolometric magnitudes Mbol to compare luminositeter. The relation Mbol − Mbol,⊙ = −2.5 log10(L/L⊙) connects luminositet to magnitude. Bolometric corrections convert observed magnitudes in a given band to bolometric values.

Applications: luminositeter are fundamental for characterizing stars, galaxies, and quasars, enabling comparisons of energy output, evolutionary states, and population statistics such as luminosity functions and luminosity density. Accurate measurements require distance estimates, extinction corrections, and modeling of spectral energy distributions.