luminosity distance اپست ِ تابندگی apast-e tâbandegi Fr.: distance de luminosité Distance derived by comparison of → observed and
→ intrinsic luminosities.
If an object has a known luminosity L, and the observed flux is
S, the luminosity distance is defined by
DL = (L/4πS)1/2.
In cosmology, the → expansion of the Universe
results in a diminution of the photon flux and the above
equation fails. The reason is that for a homogeneous
and isotropic Universe (→ Robertson-Walker metric),
the luminosity decreases by a factor (1 + z)4.
Therefore, the luminosity distance is related to the
→ angular diameter distance (DA)
by:
DL = (1 + z)2.DA.
See also: → luminosity; → distance. |
