Mattig formula
Mattig's formula is one of the most important formulae in observational cosmology and extragalactic astronomy which gives relation between radial coordinate and redshift of a given source. It depends on the cosmological model being used and is needed to calculate luminosity distance in terms of redshift.[1]
Without dark energy
Derived by W. Mattig in a 1958 paper,[2] the mathematical formulation of the relation is,[3]
Where, is the radial coordinate distance (proper distance at present) of the source from the observer while is the proper distance and is the comoving distance.
- is the deceleration parameter while is the density of matter in the universe at present.
- is scale factor at present time while is scale factor at any other time.
- is Hubble's constant at present and
- is as usual the redshift.
This equation is only valid if . When the value of cannot be calculated. From this radius we can calculate luminosity distance using the following formula,
When we get another expression for luminosity distance using Taylor expansion,
But in 1977 Terrell devised a formula which is valid for all ,[4]
References
- ↑ Observations in Cosmology, Cambridge University Press
- ↑ Mattig, W. (1958), "Über den Zusammenhang zwischen Rotverschiebung und scheinbarer Helligkeit", Astronomische Nachrichten 284: 109, Bibcode:1958AN....284..109M, doi:10.1002/asna.19572840303
- ↑ Bradley M. Peterson, "An Introduction to Active Galactic Nuclei", p. 149
- ↑ Terrell, James (1977), "The luminosity distance equation in Friedmann cosmology", Am. J. Phys., 45(9): 869–870, Bibcode:1977AmJPh..45..869T, doi:10.1119/1.11065