Redshift

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observable universe with z=0.01 to z=1089 red corrimiento

Streaming to the red of the spectral lines in the visible spectrum of a super cluster of distant galaxies (right), compared to that of the Sun (left). The wavelength increases to the red and beyond.

Red or blue correction depending on the relative movement between the emitting object and the observer.

Figure illustrating the correction to gravitational red.

In physics and astronomy, the redshift, red approaching, or redshift (in English: redshift) is a phenomenon that occurs when electromagnetic radiation that is emitted or reflected from an object, usually visible light, appears redshifted at the end of the electromagnetic spectrum. More generally, redshift is defined as an increase in the wavelength of electromagnetic radiation received by a detector compared to the wavelength emitted by the source. This increase in wavelength corresponds to a decrease in the frequency of electromagnetic radiation. Similarly, the decrease in wavelength is called the blueshift.

Any increase in wavelength is called a "redshift," even if it occurs in regions of the spectrum corresponding to non-visible electromagnetic radiation, such as gamma rays, X-rays, or ultraviolet radiation. The naming can be confusing as at wavelengths longer than red (eg infrared, microwaves, and radio waves), the "redshifts" actually move away from the red-wavelength. Even so, speaking of frequencies of waves less than red continues to mean that the wavelength tends to lengthen and not to resemble red.

A redshift can occur when a light source moves away from an observer, corresponding to a Doppler shift that changes the perceived frequency of sound waves. Although observing such redshifts—or their equivalent blueshifts—has numerous terrestrial applications (e.g., Doppler radar and radar gun), astronomical spectroscopy uses Doppler redshifts to determine the motion of objects. astronomically distant. This phenomenon was first predicted and observed in the 19th century when scientists began to consider the dynamical implications of the wave nature of light.

Another redshift mechanism is the metric expansion of space, which explains the famous observation of the spectral redshifts of distant galaxies, quasars, and intergalactic gas clouds, which increase proportionally with their distance from the observer. This mechanism is a key feature of the Big Bang model of physical cosmology.

A third type of redshift, gravitational redshift (also known as the Einstein effect), occurs as a result of time dilation near massive objects, in accordance with general relativity.

These three phenomena can be understood under the umbrella of frame transformation laws. There are many other mechanisms with very different physical and mathematical descriptions that can lead to a shift in the frequency of electromagnetic radiation and whose actions may occasionally be known as 'redshift', including scattering and various optical effects.

In astronomy, it is usual to refer to this change in wavelength using a dimensional magnitude called " $z,$ ».

History

The history of redshift began with the development in the 19th century of wave mechanics and the study of the phenomenon associated with the Doppler effect, an effect named after Christian Andreas Doppler offered the first known physical explanation for the phenomenon in 1842. The hypothesis was tested and confirmed using sound waves by the Dutch scientist Christophorus Buys Ballot in 1845. Doppler correctly predicted that the phenomenon should apply to all waves and in particular suggested that the variation in the colors of the stars could be attributed to their motion relative to the Earth. While this attribution turned out to be incorrect (the colors of the stars are indicators of temperature, not motion), Doppler would later be vindicated for verification of redshift observations.

The first Doppler redshift was described in 1848 by the French physicist Hippolyte Fizeau, who indicated that the observed shift in the spectral lines of stars was due to the Doppler effect. This is why the effect is sometimes called the "Doppler-Fizeau effect." In 1868, British astronomer William Huggins was the first to determine the speed of a star receding from Earth using this method.

In 1871, optical redshift was confirmed when the phenomenon was observed at Fraunhofer lines using solar rotation, to about 0.1 Å from red. In 1901 Aristarj Belopolsky verified optical redshift in the laboratory using a system of specular rotation.

The first appearance of the expression "redshift" in the scientific literature was due to the American astronomer Walter Sidney Adams in 1908, where he mentions "Two methods of investigating the nature of the nebular redshift".

Beginning with observations in 1912, Vesto Slipher discovered that many spiral nebulae had considerable redshifts. Edwin Hubble later discovered an approximate relationship between the redshift of such "nebulae" (now known as galaxies) and the distance to them with the formulation of his eponymous Hubble's law. These observations corroborated the work of Alexander Friedman of 1922, in which he found the famous Friedmann equations, showing that the Universe could expand and presented the rate of expansion in that case. Today they are considered strong evidence for an expanding Universe and the Big Bang Theory.

Measurement, characterization and interpretation

A redshift can be measured by looking at the spectrum of light coming from a single source. If there are features in this spectrum such as absorption lines, emission lines or other variations of light intensity, then in principle the redshift can be calculated. For this, it is necessary to compare the observed spectrum with a known spectrum with similar characteristics. For example, hydrogen, when exposed to light, has a spectrum that shows features at regular intervals. If the same pattern of intervals is observed in an observed spectrum but occurs at offset wavelengths, then the redshift of the object can be measured. To determine the redshift of an object therefore requires a range of frequencies or wavelengths. Redshifts cannot be calculated by observing unidentified features whose residual frequencies are unknown or with a spectrum that has no features or white noise (random fluctuations in a spectrum.)

The red (and blue) corrimiento can be characterized by the relative difference between the observed and emitted wavelengths (or frequencies) of an object. In astronomy, it is usual to refer to this change using a dimensioned magnitude called z. Yeah. $lambda$ represents the wavelength f frequency ( ${displaystyle lambda f=c}$ where c is the speed of light, then z is defined by equations:

**Measured from the red run, $z$**
Based on wavelength	Frequency-based
${displaystyle z={frac {lambda _{mathrm {observada} }-lambda _{mathrm {emitida} }}{lambda _{mathrm {emitida} }}}}$	${displaystyle z={frac {f_{mathrm {emitida} }-f_{mathrm {observada} }}{f_{mathrm {observada} }}}}$
${displaystyle 1+z={frac {lambda _{mathrm {observada} }}{lambda _{mathrm {emitida} }}}}$	${displaystyle 1+z={frac {f_{mathrm {emitida} }}{f_{mathrm {observada} }}}}$

After measuring z, the distinction between redshift and blueshift is simply whether z is positive or negative. For example, in blueshifts (z < 0), the Doppler shift is associated with objects approaching the observer where light is shifted to higher energies. Conversely, in redshifts (z > 0), the Doppler effect is associated with objects moving away from the observer with light moving towards lower energies. Likewise, Einstein effect blueshifts are associated with light entering a strong gravitational field while Einstein effect redshifts imply that light is leaving the field.

Mechanisms

A single photon traveling through a vacuum can be redshifted in several different ways. Each of these mechanisms produces a Doppler shift, ie z is independent of wavelength. These mechanisms are described by means of Galilean, Lorentzian or relativistic transformations between one reference system and another.

**Summary of red corrimientos**
Type of corrimiento to red	System Transformation Act	Example of metric	Definition
Doppler red correction	Transformations of Galileo	Euclidian distance	${displaystyle z={frac {v}{c}}}$
Relativist Doppler	Transformations of Lorentz	Minkowski	${displaystyle z=left(1+{frac {v}{c}}right)gamma -1}$
Cosmetic red correction	Relativist transformations	FLRW	${displaystyle z={frac {a_{mathrm {now} }}{a_{mathrm {then} }}}-1}$
Correction to gravitational red	Relativist transformations	Schwarzschild Metric	${displaystyle z={frac {1}{sqrt {1-left({frac {2GM}{rc^{2}}}right)}}}-1}$

Doppler Effect

Main article: Doppler effect

If a light source is moving away from an observer, then redshifts (z > 0) occur. If the source gets closer, then a blueshift occurs. This is valid for all electromagnetic waves and is explained by the Doppler effect. Consequently, this type of redshift is called the Doppler redshift. If the source is moving away from the observer with velocity v, then, ignoring relativistic effects, the redshift is given by

{displaystyle zapprox {frac {v}{c}}}

(Since

{displaystyle gamma approx 1}

, see below)

where c is the speed of light. In the classical Doppler effect, the source frequency is unchanged, but the recessive motion causes the illusion of a lower frequency.

Relativistic Doppler Effect

Main article: Relativistic Doppler Effect

A more complete treatment of Doppler red corrimiento needs the consideration of relativistic effects associated with the movement of sources that move quickly near the speed of light. In brief, objects moving near the speed of light will experience deviations from the simple Doppler effect formula due to the dilation of the time of special relativity that can be corrected by introducing the Lorentz factor $gamma$ in the classic Doppler formula as follows:

{displaystyle 1+z=left(1+{frac {v}{c}}right)gamma }

This phenomenon was first observed in a 1938 experiment conducted by Herbert E. Ives and G.R. Stilwell. As the Lorentz factor only depends on the magnitude of the speed, this causes the shift to red associated with relativistic correction to be independent of the orientation of the motion source. In contrast, the classic part of the formula depends on the projection of the motion of the source in the line of view that provides different results for different orientations. Consequently, for an object moving forming an angle $theta$ with the observer (the null angle has a direct line with the observer), the complete form for the relativist Doppler effect becomes:

{displaystyle 1+z={frac {1+vcos(theta)/c}{sqrt {1-v^{2}/c^{2}}}}}

and only for movements on the line of view ( $theta$ = 0°, this equation is reduced to:

{displaystyle 1+z={sqrt {frac {1+{frac {v}{c}}}{1-{frac {v}{c}}}}}}

For the special case where the source is moving in straight angles ( $theta$ = 90°) to the detector, the relativist red corrimiento is known as the transverse Doppler effect and a red corrimiento of:

{displaystyle 1+z={frac {1}{sqrt {1-v^{2}/c^{2}}}}}

is measured, even though the object is not moving away from the observer. Even if the source is moving toward the observer, if there is a transverse component to the motion then there is some velocity at which the dilation exactly cancels the expected blueshift, and at higher velocities the approaching source would be redshifted.

Space Expansion

Main article: Metric of expansion of the universe

Galaxys with great displacement towards the red of Hubble's ultra-deep field.

In the first part of the centuryXX.Slipher, Hubble and others made the first measures of corrimientos to the red and blue of galaxies beyond the Milky Way. Initially they interpreted these shifts to red and blue as due only to the Doppler effect, but Hubble then discovered a slight correlation between the increase in displacement to red and the increase in galaxy distance. Theoreticians almost immediately realized that these observations could be explained by a different mechanism of corruption to the red. Hubble's law of the correlation between red corrimientos and distances is required by the cosmology models from the general relativity that have a metric expansion of space. As a result, photons spreading through the expanding Universe are extended, creating the Cosmetic red corrimiento. This differs from the shifts to red by Doppler effect described earlier because the push speed (e.g. the transformation of Lorentz) between the source and the observer is not due to the classic transfer between time and energy, but instead the photons increase their wavelength and move towards the red according to the space they are going through is expanded. This effect is prescribed in the current cosmological model as an observable manifestation of the time-dependent cosmic scale factor ( $a$ ) as follows:

{displaystyle 1+z={frac {a_{mathrm {ahora} }}{a_{mathrm {entonces} }}}.}

This type of redshift is called cosmological redshift or Hubble redshift. If the Universe were contracting instead of expanding, we would see distant galaxies blueshifting by an amount proportional to their distance instead of redshifting.

These galaxies are not simply receding by physical velocity away from the observer, rather the intervening space is stretching out, which accounts for the large-scale isotropy effect demanded by the cosmological principle. For cosmological redshifts with z < 0.1 the effects of spacetime expansion are minimal and the redshifts are dominated by the peculiar relative motions between one galaxy to another that cause additional Doppler redshifts and blueshifts. The difference between physical velocity and expansion of space can be illustrated by the Rubber Sheet Expansion of the Universe, a common cosmological analogy used to describe the expansion of space. If two objects are represented by ball bearings and space-time by an expanding rubber sheet, the Doppler effect is caused by the rolling of the balls across the sheet creating a particular motion. Cosmological redshift occurs when the bearing balls stick to the sheet and the sheet is expanded. (Obviously, there are dimensional problems with the model, since the ball bearings should be on the sheet, and the redshift produces velocities greater than the Doppler shift if the distance between two objects is far enough. long.).

Despite the distinction between redshifts caused by the speed of objects and those associated with the expansion of the Universe, astronomers sometimes refer to it as "recession velocity" in the context of redshifts of distant galaxies from the expansion of the Universe, even though it is only an apparent recession. As a consequence, popular literature often uses the expression "Doppler redshift" instead of "cosmological redshift" to describe the motion of galaxies dominated by the expansion of space, despite the fact that a "recessive cosmological velocity" when calculated it will not equal velocity in the relativistic Doppler equation. In particular, the Doppler redshift is bounded by special relativity; so v > c is impossible while, in contrast, v > c is possible for cosmological redshifts because the space separating objects (eg a quasar from Earth) can expand faster than the speed of light. More mathematically, the point of view that "distant galaxies are receding" and the view that "the space between galaxies is expanding" It is related to the change of coordinate system. Expressing it precisely requires working with the mathematics of the Friedman-Lemaître-Robertson-Walker metric.

Mathematic derivation

The observational consequences of this effect can be deduced using the equations of the general relativity describing a homogeneous and isotropic universe. To get the expression of the corrimiento to red, it is part of the equation of a geodésica for a luminous wave, which is:

{displaystyle ds^{2}=0=-c^{2}dt^{2}+{a^{2}dr^{2} over 1-kr^{2}}}

where:

$ds^{2}$ is the space-time interval
${displaystyle dt^{2}}$ is the time interval
${displaystyle dr^{2}}$ is the space interval
c is the speed of light
a is scale factor, dependent on cosmic time
k is the Gaussian curvature

For an observer who observes the crest of a luminous wave in a position ${displaystyle r=0}$ and in a time t = ${displaystyle t_{mathrm {ahora} }}$ , the ridge of the luminous wave was emitted in t = ${displaystyle t_{mathrm {entonces} }}$ in the past and from a distant position ${displaystyle r=R}$ . The integration on the trajectory in both the space and the time on which the luminous wave travels provides:

{displaystyle cint _{t_{mathrm {entonces} }}^{t_{mathrm {ahora} }}{frac {dt}{a}};=int _{R}^{0}{frac {dr}{sqrt {1-kr^{2}}}},}

In general, the wavelength of light is not the same in the two positions and times contemplated due to the changing characteristics of the metric. When the wave was emitted, it had a wavelength ${displaystyle lambda _{mathrm {entonces} }}$ . The following crest of the luminous wave was emitted in a time:

${displaystyle t=t_{mathrm {entonces} }+lambda _{mathrm {entonces} }/c,}$

The observer sees that the next crest of the observed luminous wave, with a wavelength ${displaystyle lambda _{mathrm {ahora} }}$ He arrives in a time:

{displaystyle t=t_{mathrm {ahora} }+lambda _{mathrm {ahora} }/c,}

From this posterior crest has also been emitted from ${displaystyle r=R}$ and is observed in ${displaystyle r=0}$ , you can write the following equation:

{displaystyle cint _{t_{mathrm {entonces} }+lambda _{mathrm {entonces} }/c}^{t_{mathrm {ahora} }+lambda _{mathrm {ahora} }/c}{frac {dt}{a}};=int _{R}^{0}{frac {dr}{sqrt {1-kr^{2}}}},}

The right side of the two integral equations above are identical, therefore:

{displaystyle cint _{t_{mathrm {entonces} }+lambda _{mathrm {entonces} }/c}^{t_{mathrm {ahora} }+lambda _{mathrm {ahora} }/c}{frac {dt}{a}};=cint _{t_{mathrm {entonces} }}^{t_{mathrm {ahora} }}{frac {dt}{a}},}

Operating:

{displaystyle {begin{aligned}0&=int _{t_{mathrm {entonces} }}^{t_{mathrm {ahora} }}{frac {dt}{a}}-int _{t_{mathrm {entonces} }+lambda _{mathrm {entonces} }/c}^{t_{mathrm {ahora} }+lambda _{mathrm {ahora} }/c}{frac {dt}{a}}\&=int _{t_{mathrm {entonces} }}^{t_{mathrm {entonces} }+lambda _{mathrm {entonces} }/c}{frac {dt}{a}}+int _{t_{mathrm {entonces} }+lambda _{mathrm {entonces} }/c}^{t_{mathrm {ahora} }}{frac {dt}{a}}-int _{t_{mathrm {entonces} }+lambda _{mathrm {entonces} }/c}^{t_{mathrm {ahora} }+lambda _{mathrm {ahora} }/c}{frac {dt}{a}}\&=int _{t_{mathrm {entonces} }}^{t_{mathrm {entonces} }+lambda _{mathrm {entonces} }/c}{frac {dt}{a}}-left(int _{t_{mathrm {now} }}^{t_{mathrm {entonces} }+lambda _{mathrm {entonces} }/c}{frac {dt}{a}}+int _{t_{mathrm {entonces} }+lambda _{mathrm {entonces} }/c}^{t_{mathrm {ahora} }+lambda _{mathrm {ahora} }/c}{frac {dt}{a}}right)\&=int _{t_{mathrm {entonces} }}^{t_{mathrm {entonces} }+lambda _{mathrm {entonces} }/c}{frac {dt}{a}}-int _{t_{mathrm {ahora} }}^{t_{mathrm {ahora} }+lambda _{mathrm {ahora} }/c}{frac {dt}{a}}end{aligned}}}

Finally you get

{displaystyle int _{t_{mathrm {ahora} }}^{t_{mathrm {ahora} }+lambda _{mathrm {ahora} }/c}{frac {dt}{a}};=int _{t_{mathrm {entonces} }}^{t_{mathrm {entonces} }+lambda _{mathrm {entonces} }/c}{frac {dt}{a}},}

For very small variations in time (as is a period of a luminous wave) the scale factor is essentially a constant ( ${displaystyle a=a_{mathrm {ahora} }}$ and ${displaystyle a=a_{mathrm {antes} }}$ ). This allows to simplify the integrals:

${displaystyle {frac {t_{mathrm {ahora} }+lambda _{mathrm {ahora} }/c}{a_{mathrm {ahora} }}}-{frac {t_{mathrm {ahora} }}{a_{mathrm {ahora} }}};={frac {t_{mathrm {entonces} }+lambda _{mathrm {entonces} }/c}{a_{mathrm {entonces} }}}-{frac {t_{mathrm {entonces} }}{a_{mathrm {entonces} }}}}$

that can be rewritten as

{displaystyle {frac {lambda _{mathrm {ahora} }}{lambda _{mathrm {entonces} }}}={frac {a_{mathrm {ahora} }}{a_{mathrm {entonces} }}},}

Using the definition of corrimiento to the red provided above, you get the expression of the corrimiento to the cosmological red based on the scale factor you were looking for:

{displaystyle 1+z={frac {a_{mathrm {ahora} }}{a_{mathrm {entonces} }}}}

In a universe like the one we inhabit that expands, the scale factor increases monotonously with time, so, z is positive and the distant galaxies appear with red corrimiento. Using a model of the expansion of the Universe, the corrimiento to red can be related to the age of a observed object, called cosmic-corrupted time ratio. Given a density relationship like ${displaystyle Omega _{0}}$ :

{displaystyle Omega _{0}={frac {rho }{rho _{text{crit}}}}}

Where ${displaystyle rho _{text{crit}}}$ is the critical density of the expanding universe. Large red corrimientos are found:

{displaystyle t(z)={frac {2}{3H_{0}{Omega _{0}}^{1/2}(1+z)^{3/2}}}}

Where $H_0$ is the current Hubble constant, and z is the red corrimiento.

Gravitational Redshift

In the theory of general relativity, time dilation exists within gravitational wells. This is known as the gravitational redshift or Einstein shift. Theoretical proof of this effect is obtained from the Schwarzschild solution of Einstein's equations, of which the redshift associated with a photon traveling through the gravitational field generated by a spherically symmetric mass, without electric charge and non-rotating, can be obtained:

{displaystyle 1+z={frac {1}{sqrt {1-left({frac {2GM}{rc^{2}}}right)}}}}

where:

$G,$ is the gravitational constant,
$M,$ is the mass of the object that creates the gravitational field,
$r,$ is the radial coordinate of the observer (which is analogous to the classic distance from the center of the object, but really is a Schwarzschild coordinate), and
$c,$ It's the speed of light.

This gravitational redshift can be calculated from the assumption of special relativity and the equivalence principle; the full theory of general relativity is not necessary.

The effect is very small but measurable on Earth using the Mossbauer effect, and was first observed in Pound and Rebka's experiment. However, it is significant near a black hole, and when an object approaches At the event horizon the redshift tends to infinity. It is also the dominant cause of the large angular-scale temperature fluctuations in the cosmic microwave background (see the Sachs-Wolfe effect).

Astronomical Observations

The redshift observed in astronomy can be measured because the emission and absorption spectra for atoms are distinctive, calibrated from spectroscopy experiments in terrestrial laboratories. When the redshift of various absorption and emission lines from a single astronomical object is measured, z is found to be extraordinarily constant. Although distant objects may be slightly blurred and the lines broadened, it is only because it can be explained by the thermal and mechanical motions of the source. For these and other reasons, the consensus among astronomers is that the redshifts they observe are due to some combination of these three established forms of Doppler-style redshifts. Alternative hypotheses are not generally considered plausible.

Spectroscopy, as a measurement, is considerably more difficult than simple photometry, which measures the brightness of astronomical objects through filters. When photometric data are the only ones available (for example, in the Hubble Deep Field and the Hubble Ultra Deep Field), astronomers rely on a technique for measuring photometric redshifts. Due to the sensitivity of the filtering over a range of wavelengths and the technique relying on many assumptions about the nature of the spectrum at a light source, the errors for these types of measurements can be in the ranges greater than z = 0.5 and are much less reliable than spectroscopic resolutions. However, photometry allows at least qualitative characterization of a redshift. For example, if a solar-like spectrum has a redshift of z = 1, it would be brighter in the infrared than in the yellow-green color associated with the peak of its blackbody spectrum and the Light intensity will be reduced in the filter by a factor of two (1 +z) (see the K correction for more details on the photometric consequences of redshift).

Local Observations

In nearby objects (within our Milky Way), the observed redshifts are almost always related to the LOS velocities associated with the objects being observed. Observations of such redshifts and blueshifts have allowed astronomers to measure velocities and parameterize the masses of stellar orbits in spectroscopic binaries, a method first employed in 1868 by British astronomer William Huggins. Small redshifts and blueshifts detected in spectroscopic measurements of individual stars are one way astronomers can diagnose and measure the presence and characteristics of planetary systems around other stars. Redshift measurements for fine details are used in helioseismology to determine the precise motions of the Sun's photosphere. Redshifts have also been used to make the first measurements of the rotation of the planets, interstellar cloud velocities, the rotation of galaxies, and the dynamics of the sun. accretion disk in neutron stars and black holes that exhibit displacement Doppler and gravitational redshifts. Additionally, the emission and absorption temperatures of various objects can be obtained by measuring the Doppler broadening, redshifts, and blueshifts along a single line of absorption or emission. Measuring the broadening and shifts Within 21-centimeters of the hydrogen line in different directions, astronomers have been able to measure the recession velocities of interstellar gas, which ultimately revealed the rotation curve of our Milky Way. Similar measurements have been made on other galaxies, such as that of Andromeda. As a diagnostic tool, redshift measurements are one of the most important spectroscopic measurements made in astronomy.

Intergalactic Observations

The most distant objects exhibit the largest redshifts corresponding to the Hubble flow of the Universe. The largest displacements observed, corresponding to the greatest distances and the furthest back in time, are those of cosmic microwave radiation and the numerical value of its displacement, according to the best currently available measurements, which are those published by the Planck Collaboration in 2018, it is approximately z = 1089.8 (z = 0 corresponds to the present moment) and shows the state of the Universe about 13787 million years ago and 372000 years later of the initial moments of the Big Bang.

The specific luminous nuclei of the quasars were the first "highly-displaced objects to the red"( $0.1}" xmlns="http://www.w3.org/1998/Math/MathML">z▪0.1{displaystyle zgs0.1}0.1}" aria-hidden="true" class="mwe-math-fallback-image-inline" src="https://wikimedia.org/api/rest_v1/media/math/render/svg/4f490d8b70333a4c41c3fdde70f471717ce9a694" style="vertical-align: -0.338ex; width:7.158ex; height:2.176ex;"/>$ ) discovered before the improvement of the telescopes allowed the discovery of other highly displaced galaxies. Currently, the highest measured quasar red corrimiento is ${displaystyle z=6.4}$ , with confirmation that the greatest red rush of a galaxy is ${displaystyle z=7.0}$ while other unconfirmed reports more than a gravitational lens observed in a cluster of distant galaxies may indicate that a galaxy has a shift to red ${displaystyle z=10}$ .

For galaxies farther away from the Local Group and close to the Virgo Cluster, but within a few thousand megaparsecs, the redshift is roughly proportional to the distance from the galaxy. This correlation was observed by Edwin Hubble and is known as Hubble's law. Vesto Slipher was the discoverer of galactic redshifts. Around 1912, while Hubble was correlating Slipher's measurements with distances, he measured them by other means to formulate his Law. In the widely accepted model based on general relativity, redshifts are primarily a result of the expansion of the space: this means that the beyond of a galaxy is from us, most of the space has expanded in the time since the light left the galaxy, so most of the light has spread out, most of the light has it has redshifted and so it appears to be moving away from us. Hubble's law comes in part from the Copernican principle. Since it is not normally known how luminous objects are, measurement of redshift is easier than more direct distance measurements, so redshifts are sometimes converted to a measure of distance using Hubble's law.

The gravitational interactions of galaxies with each other and with clusters cause scattering in the normal pattern of the Hubble diagram. The peculiar velocities associated with overlapping galaxies leaving a rough trail of mass from virialized objects in the Universe. This effect leads to such a phenomenon as nearby galaxies (like the Andromeda galaxy) exhibiting blueshifts as we fall toward a common barycenter and cluster redshift maps show a Finger of God due to the scattering of peculiar velocities in a spherical distribution. This added component gives cosmologists an opportunity to measure the masses of objects independent of the light-mass ratio (the ratio of the mass of a galaxy in solar masses with its brightness in solar luminosities), an important tool for measuring dark matter.

Hubble's law linear relationship between distance and redshift assumes that the expansion rate of the Universe is constant. However, when the Universe was much younger, the rate of expansion and then the "constant" Hubble was larger than it is today. For more distant galaxies, whose light has been traveling much longer, the constant expansion rate approximation fails and Hubble's law becomes a non-linear integral relationship dependent on the history of the expansion rate since the emission of light from the galaxy in question. Observations of the redshift distance relationship can then be used to determine the expansion history of the Universe and thus the matter and energy contained.

For a long time it was believed that the rate of expansion had been continuously decreasing since the Big Bang, recent observations of the redshift distance relationship using type Ia supernovae have suggested that in comparatively recent times the Universe has begun to accelerate.

Redshift in expeditions

With the advent of automated telescopes and improvements in spectroscopes, several collaborations have been made to map the Universe at the redshift of space. By combining these redshifts with angular position data, a redshift expedition maps the 3D distribution of matter within a part of the sky. These observations often measure properties of the large-scale structure of the universe. The Great Wall, a large supercluster of galaxies some 500 million light-years away, provides a dramatic example of a large-scale structure that redshift expeditions can detect.

The first redshift expedition was the CfA Redshift Survey, which began in 1977 and completed initial data collection in 1982. More recently, the 2dF Galaxy Redshift Survey found the structure at large scale of a section of the Universe, measuring z values of more than 220,000 galaxies, data collection was completed in 2002 and the final data set was released on June 30, 2003. (In addition to large-scale mapping patterns of galaxies, the 2dF set an upper limit for neutrino mass.) Another notable expedition, the Sloan Digital Sky Survey (SDSS), is ongoing (at least in 2005) and attempts to obtain measurements of about 100 million objects. The SDSS has recorded redshifts for galaxies above 0.4 and has been involved in the detection of quasars beyond z = 6. The DEEP2 Redshift Survey uses the Keck telescopes with the new "DEIMOS]] spectrograph. A follow-up to the DEEP1 pilot program, DEEP2 is designed to measure faint galaxies with redshifts of 0.7 and higher and is therefore planned to complement SDSS and 2dF.

Higher redshifts

Distance chart (in gigantic light years) vs. shift to red according to the Lambda-CDM model.

The objects with the largest redshifts are galaxies and gamma-ray bursts. The most reliable samples come from spectral analyses, the redshift confirmed as the highest being that of the galaxy GN-z11, with z=11.1, that is, 400 million years after the Big Bang. The object that previously The most distant gamma-ray burst is the galaxy UDFy-38135539, with a value of z=8.6. The most distant gamma-ray burst is GRB 090423, discovered in April 2009, it has a redshift of z =8.2. While ULAS J1342+0928 is the most distant known quasar, with a value of z=7.54. The most distant radio galaxy is TN J0924-2201 and has an offset of z=5.2. The most distant molecular material Known far distance is a CO emission from the quasar SDSS J1148 + 5251, with a redshift of z=6.42.

Extremely Red Objects (EROs) are astronomical sources of radiation that emit energy in the red and infrared parts of the electromagnetic spectrum. Such as galaxies with a high star formation rate, or elliptical galaxies with an older stellar population. According to the latest measurements published by the Planck Collaboration in 2018, the microwave background radiation corresponds to a redshift of z=1089.8, that is, it was born about 372,000 years after the Big Bang, and the current distance to the last scattering surface is more than 45 billion light years. In June 2015 it was reported that stars in galaxies emitting Lyman-alpha radiation indicate values of z=6.60. It is likely that such stars existed in a very early universe and began the creation of chemical elements heavier than hydrogen, which are necessary for the formation of planets and any type of life.

Effects due to optical or radioactive transfers

The interactions and phenomena outlined in the subjects of radioactive transfer and physical optics can result in shifts in the wavelength and frequency of electromagnetic radiation. In such cases the displacements correspond to a physical transfer of energy to matter or other photons rather than due to a transformation between reference frames. These displacements may be due to such physical phenomena as the Wolf effect or the scattering of electromagnetic radiation from charged elementary particles, from particles or from refractive index fluctuations in a dielectric medium as occurs in the phenomenon of radio whistles. While such phenomena are known as "redshifts" and "blueshifts", the physical interactions of electromagnetic radiation fields with proper or intermediate matter distinguishes these phenomena from reference frame effects. In astrophysics, the light-matter interactions that provide energy shifts in the radiation field are generally known as "flushing" rather than "redshifted", which as a term, is normally reserved for the mechanisms discussed above.

In many circumstances scattering causes radiation to redden because entropy results from the predominance of many low-energy photons over a few high-energy ones (observing the principle of conservation of energy). Except possibly under carefully controlled, the scattering does not produce the same relative change in wavelength across the entire spectrum; that is, any calculated z is generally a function of wavelength. Further, the scattering of random matter generally occurs at many angles and z is a function of the scattering angle. If multiple scattering occurs or the scattered particles have relative mobility, then spectral line distortion usually also occurs.

In interstellar astronomy, the visible spectrum can appear reddened due to scattering processes in a phenomenon known as interstellar reddening. Similarly Rayleigh scattering causes the atmospheric reddening of the Sun seen in the sunrise or sunset and causes the rest of the sky to appear blue. This phenomenon is distinct from redshift because the spectroscopic lines are not shifted to other wavelengths in reddened objects and there is additional dimming and distortion associated with the phenomenon due to photons being scattered within. and out of the LOS.

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