redshift


Also found in: Dictionary, Thesaurus, Wikipedia.
Related to redshift: Gravitational redshift

redshift

(red -shift) A displacement of spectral lines toward longer wavelength values; for an optical line, the shift would be toward the red end of the visible spectrum. The redshift parameter, z, is given by the ratio δλ/λ, where δλ is the observed increase in wavelength of the radiation and λ is the wavelength of the spectral line at the time of emission from a source, i.e. the wavelength in the ‘normal’ terrestrial spectrum.

The redshifts of astronomical objects within the Galaxy are interpreted as Doppler shifts (see Doppler effect) caused by movement of the source away from the observer. The value of z is then v /c , where v is the relative radial velocity and c is the speed of light. The redshifts of extragalactic sources, including quasars, are also interpreted in terms of the Doppler effect, which for these objects results from the expansion of the Universe. The redshift parameter of a distant galaxy thus gives its velocity of recession; since recessional velocities can be very great, the relativistic expression for redshift must be used:

z = [(c + v )/(c v )]½ – 1

From measurements of galactic redshifts it has been possible to calculate the distances of galaxies, using Hubble's law (see distance determination).

The redshifts described above represent a loss of energy by the photons of radiation in overcoming the effects of recession or expansion. There is another mechanism, however, by which redshifts can be produced, i.e. by which photons can lose energy – the presence of a strong gravitational field. This gravitational redshift was predicted by Einstein in his general theory of relativity. Although the redshifts of galaxies are often interpreted as being caused by the relativistic Doppler effect alone, both the expansion and the gravitational field of the Universe are involved. See also cosmological redshift.

Collins Dictionary of Astronomy © Market House Books Ltd, 2006

redshift

[′red‚shift]
(astrophysics)
A systematic displacement toward longer wavelengths of lines in the spectra of distant galaxies and also of the continuous portion of the spectrum; increases with distance from the observer. Also known as Hubble effect.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
"I'd like to title my book something like Redshift: The Key to Cosmology."
Also, the prevading gravitational fields of other universes in and of themselves would effect a redshift. However, we do not see stellar objects from these other universes being accelerated into our own, and retrogressively being blueshifted by moving toward us.
If, on the other hand, mergers beyond the redshift of 40 were found to not be primordial, it would mean that matter distribution in the universe is not based on Gaussian probability.
Because dt = da/Ha, where a is the scale factor, the proper light-travel time versus redshift is:
Turning this around, by measuring the rate at which a quasar's light appears to vary and comparing this rate to the standard rate at which quasars sampled actually vary, the researchers were able to infer the redshift of the quasar.
"Phallacy" scribe Carl Djerassi also happens to be one of the inventors of the birth control pill, which makes him a poster boy for Redshift's mission.
This redshift would span the entire electromagnetic spectrum.
Dissenters also (http://curious.astro.cornell.edu/about-us/110-the-universe/cosmology-and-the-big-bang/alternate-theories/670-can-tired-light-theory-explain-the-observed-redshifts-of-galaxies-intermediate) argue that a redshift on the electromagnetic spectrum is not the only information scientists have supporting an expanding universe, while the concept of tired light does not take those other elements into consideration.
Recent long-exposure Hubble images taken by Mark Dickinson (now at the National Optical Astronomy Observatory) had shown misshapen "train-wreck" galaxies at a redshift of 1.2, corresponding to a look-back time of two-thirds of the age of the universe.