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Mattig Formula
Mattig's formula was an important formula 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 used to calculate luminosity distance in terms of redshift. It assumes zero dark energy, and is therefore no longer applicable in modern cosmological models such as the Lambda-CDM model, (which require a numerical integration to get the distance-redshift relation). However, Mattig's formula was of considerable historical importance as the first analytic formula for the distance-redshift relationship for arbitrary matter density, and this spurred significant research in the 1960s and 1970s attempting to measure this relation. Without dark energy Derived by W. Mattig in a 1958 paper, the mathematical formulation of the relation is, r_1 = \frac \frac Where, r_1=\frac=\frac is the radial coordinate distance (proper distance at present) of the source from t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Observational Cosmology
Observational cosmology is the study of the structure, the evolution and the origin of the universe through observation, using instruments such as telescopes and cosmic ray detectors. Early observations The science of physical cosmology as it is practiced today had its subject material defined in the years following the Shapley-Curtis debate when it was determined that the universe had a larger scale than the Milky Way galaxy. This was precipitated by observations that established the size and the dynamics of the cosmos that could be explained by Albert Einstein's General Theory of Relativity. In its infancy, cosmology was a speculative science based on a very limited number of observations and characterized by a dispute between steady state theorists and promoters of Big Bang cosmology. It was not until the 1990s and beyond that the astronomical observations would be able to eliminate competing theories and drive the science to the "Golden Age of Cosmology" which was heralde ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Extragalactic Astronomy
Extragalactic astronomy is the branch of astronomy concerned with objects outside the Milky Way galaxy. In other words, it is the study of all astronomical objects which are not covered by galactic astronomy. The closest objects in extragalactic astronomy include the galaxy, galaxies of the Local Group, which are close enough to allow very detailed analyses of their contents (e.g. supernova remnants, Stellar kinematics#Stellar associations, stellar associations). As instrumentation has improved, distant objects can now be examined in more detail and so extragalactic astronomy includes objects at nearly the edge of the observable universe. Research into distant galaxies (outside of our local group) is valuable for studying aspects of the universe such as galaxy evolution and Active galactic nucleus, Active Galactic Nuclei (AGN) which give insight into physical phenomena (e.g. Supermassive black hole, super massive black hole accretion and the presence of dark matter). It is through ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Redshift
In physics, a redshift is an increase in the wavelength, and corresponding decrease in the frequency and photon energy, of electromagnetic radiation (such as light). The opposite change, a decrease in wavelength and increase in frequency and energy, is known as a #Blueshift, blueshift. The terms derive from the colours red and blue which form the extremes of the Visible spectrum, visible light spectrum. Three forms of redshift occur in astronomy and cosmology: Doppler effect, Doppler redshifts due to the relative motions of radiation sources, gravitational redshift as radiation escapes from gravitational potentials, and cosmological redshifts of all light sources proportional to their distances from Earth, a fact known as Hubble's law that implies the expansion of the universe, universe is expanding. All redshifts can be understood under the umbrella of Frame of reference, frame transformation laws. Gravitational waves, which also travel at Speed of light, the speed of light, a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cosmological Model
Physical cosmology is a branch of cosmology concerned with the study of cosmological models. A cosmological model, or simply cosmology, provides a description of the largest-scale structures and dynamics of the universe and allows study of fundamental questions about its origin, structure, evolution, and ultimate fate.For an overview, see Cosmology as a science originated with the Copernican principle, which implies that celestial bodies obey identical physical laws to those on Earth, and Newtonian mechanics, which first allowed those physical laws to be understood. Physical cosmology, as it is now understood, began in 1915 with the development of Albert Einstein's general theory of relativity, followed by major observational discoveries in the 1920s: first, Edwin Hubble discovered that the universe contains a huge number of external galaxies beyond the Milky Way; then, work by Vesto Slipher and others showed that the universe is expanding. These advances made it possi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Luminosity Distance
Luminosity distance ''DL'' is defined in terms of the relationship between the absolute magnitude ''M'' and apparent magnitude ''m'' of an astronomical object. : M = m - 5 \log_\!\, which gives: : D_L = 10^ where ''DL'' is measured in parsecs. For nearby objects (say, in the Milky Way) the luminosity distance gives a good approximation to the natural notion of distance in Euclidean space. The relation is less clear for distant objects like quasars far beyond the Milky Way since the apparent magnitude is affected by spacetime curvature, redshift, and time dilation. Calculating the relation between the apparent and actual luminosity of an object requires taking all of these factors into account. The object's actual luminosity is determined using the inverse-square law and the proportions of the object's apparent distance and luminosity distance. Another way to express the luminosity distance is through the flux-luminosity relationship, : F = \frac where is flux (W·m−2), an ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dark Energy
In physical cosmology and astronomy, dark energy is a proposed form of energy that affects the universe on the largest scales. Its primary effect is to drive the accelerating expansion of the universe. It also slows the rate of structure formation. Assuming that the lambda-CDM model of cosmology is correct, dark energy dominates the universe, contributing 68% of the total energy in the present-day observable universe while dark matter and Baryon#Baryonic matter, ordinary (baryonic) matter contribute 27% and 5%, respectively, and other components such as neutrinos and photons are nearly negligible.Sean Carroll, Ph.D., Caltech, 2007, The Teaching Company, ''Dark Matter, Dark Energy: The Dark Side of the Universe'', Guidebook Part 2. p. 46. Retrieved 7 October 2013, "...dark energy: A smooth, persistent component of invisible energy, thought to make up about 70 percent of the energy density of the universe. Dark energy is smooth because it doesn't accumulate preferentially in galaxi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lambda-CDM Model
The Lambda-CDM, Lambda cold dark matter, or ΛCDM model is a mathematical model of the Big Bang theory with three major components: # a cosmological constant, denoted by lambda (Λ), associated with dark energy; # the postulated cold dark matter, denoted by CDM; # ordinary matter. It is the current ''standard model'' of Big Bang cosmology, as it is the simplest model that provides a reasonably good account of: * the existence and structure of the cosmic microwave background; * the large-scale structure in the distribution of galaxies; * the observed abundances of hydrogen (including deuterium), helium, and lithium; * the accelerating expansion of the universe observed in the light from distant galaxies and supernovae. The model assumes that general relativity is the correct theory of gravity on cosmological scales. It emerged in the late 1990s as a concordance cosmology, after a period when disparate observed properties of the universe appeared mutually inconsistent, and ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Astronomische Nachrichten
''Astronomische Nachrichten'' (''Astronomical Notes''), one of the first international journals in the field of astronomy, was established in 1821 by the German astronomer Heinrich Christian Schumacher. It claims to be the oldest astronomical journal in the world that is still being published. The publication today specializes in articles on solar physics, extragalactic astronomy, cosmology, geophysics, and instrumentation for these fields. All articles are subject to peer review. Early history The journal was founded in 1821 by Heinrich Christian Schumacher,''Publications of the Astronomical Society of the Pacific'', page 60, v.7 (1895) under the patronage of Christian VIII of Denmark, and quickly became the world's leading professional publication for the field of astronomy. Schumacher edited the journal at the Altona Observatory, then under the administration of Denmark, later part of Prussia, and today part of the German city of Hamburg. Schumacher edited the first 31 issu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Proper Distance
Proper length or rest length is the length of an object in the object's rest frame. The measurement of lengths is more complicated in the theory of relativity than in classical mechanics. In classical mechanics, lengths are measured based on the assumption that the locations of all points involved are measured simultaneously. But in the theory of relativity, the notion of simultaneity is dependent on the observer. A different term, proper distance, provides an invariant measure whose value is the same for all observers. ''Proper distance'' is analogous to proper time. The difference is that the proper distance is defined between two spacelike-separated events (or along a spacelike path), while the proper time is defined between two timelike-separated events (or along a timelike path). Proper length or rest length The ''proper length'' or ''rest length'' of an object is the length of the object measured by an observer which is at rest relative to it, by applying standard m ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Comoving Distance
In standard cosmology, comoving distance and proper distance (or physical distance) are two closely related distance measures used by cosmologists to define distances between objects. ''Comoving distance'' factors out the expansion of the universe, giving a distance that does not change in time except due to local factors, such as the motion of a galaxy within a cluster. ''Proper distance'' roughly corresponds to where a distant object would be at a specific moment of cosmological time, which can change over time due to the expansion of the universe. Comoving distance and proper distance are defined to be equal at the present time. At other times, the Universe's expansion results in the proper distance changing, while the comoving distance remains constant. Comoving coordinates Although general relativity allows the formulation of the laws of physics using arbitrary coordinates, some coordinate choices are easier to work with. Comoving coordinates are an example of such a coor ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Deceleration Parameter
The deceleration parameter q in cosmology is a dimensionless measure of the cosmic acceleration of the expansion of space in a Friedmann–Lemaître–Robertson–Walker universe. It is defined by: q \ \stackrel\ -\frac where a is the scale factor of the universe and the dots indicate derivatives by proper time. The expansion of the universe is said to be "accelerating" if \ddot > 0 (recent measurements suggest it is), and in this case the deceleration parameter will be negative. The minus sign and name "deceleration parameter" are historical; at the time of definition \ddot was expected to be negative, so a minus sign was inserted in the definition to make q positive in that case. Since the evidence for the accelerating universe in the 1998–2003 era, it is now believed that \ddot is positive therefore the present-day value q_0 is negative (though q was positive in the past before dark energy became dominant). In general q varies with cosmic time, except in a few specia ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Scale Factor
In affine geometry, uniform scaling (or isotropic scaling) is a linear transformation that enlarges (increases) or shrinks (diminishes) objects by a '' scale factor'' that is the same in all directions ( isotropically). The result of uniform scaling is similar (in the geometric sense) to the original. A scale factor of 1 is normally allowed, so that congruent shapes are also classed as similar. Uniform scaling happens, for example, when enlarging or reducing a photograph, or when creating a scale model of a building, car, airplane, etc. More general is scaling with a separate scale factor for each axis direction. Non-uniform scaling (anisotropic scaling) is obtained when at least one of the scaling factors is different from the others; a special case is directional scaling or stretching (in one direction). Non-uniform scaling changes the shape of the object; e.g. a square may change into a rectangle, or into a parallelogram if the sides of the square are not parallel to the s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
