redshift

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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.

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.
References in periodicals archive ?
If we could measure the redshifts of millions of quasars, we could use them to map the structures in the universe out to a large redshift," Starkman noted.
The light travel time versus redshift is computed as follows (derived from dt = da/[?
We've pushed the experiment's design to a redshift of 7 - it's the most distant we can do with well-established, mature technology, and it's about the most distant where people have been finding objects successfully up to now," he added.
A more ambitious mapping, the Sloan Digital Sky Survey, aims to complete redshift measurements for 1 million galaxies--a quarter of the sky--by 2004, reaching a depth of nearly 8 billion light-years.
Based on the change of measure between LTD and Euclidean Distances, a formula that expresses distances versus redshifts is obtained.
The 2MASS Redshift Survey is a wonderfully complete new look at the local universe -- particularly near the Galactic plane," Masters said.
The current record-holder for distance is a gamma ray burst, discovered in April, with a redshift of 8.
Previous maps constructed from the same infrared data were based on redshift determinations for only about one-third as many galaxies, excluding many of the faintest ones.
Below is shown the derivation of the redshift adjusted distance modulus.
Until now, the record holder for the farthest galaxy had a spectroscopically confirmed redshift of 6.
To date, about 440 of 1,400 ultraviolet dropouts have turned out be faraway galaxies with redshifts between 2.
Two approaches are available for converting the redshifts from observed galaxies into LTDs, one based on cosmological redshifts and the other one on dopplerian redshifts.