Overblog Suivre ce blog
Editer l'article Administration Créer mon blog
28 juin 2013 5 28 /06 /juin /2013 08:17

lie in a straight line, the original light source will appear as a ring around the massive lensing object. SONY VAIO VGN-NW11S/S Laptop Keyboard

If there is any misalignment the observer will see an arc segment instead. This phenomenon was first mentioned in 1924 by the St. Petersburg physicist Orest Chwolson,[1] and quantified by Albert Einstein in 1936. It is usually referred to in the literature as anEinstein ring, since Chwolson did not concern himself with the flux or radius of the ring image. More commonly, where the lensing mass is complex (such as galaxy groups and clusters) Lenovo 3000 Y500 Laptop Keyboard

and does not cause a spherical distortion of space–time, the source will resemble partial arcs scattered around the lens. The observer may then see multiple distorted images of the same source; the number and shape of these depending upon the relative positions of the source, lens, and observer, and the shape of the gravitational well of the lensing object.[2]

There are three classes of gravitational lensing:[3] GATEWAY AEPA6TAU111 Laptop Keyboard

1. Strong lensing: where there are easily visible distortions such as the formation of Einstein rings, arcs, and multiple images.

2.  FUJITSU CP254840-01 Laptop Keyboard

The lensing shows up statistically as a preferred stretching of the background objects perpendicular to the direction to the center of the lens. By measuring the shapes and orientations of large numbers of distant galaxies, their orientations can be averaged to measure the shear of the lensing field in any region. This, in turn, can be used to reconstruct the mass distribution in the area: HP Pavilion dv6-3178ee Laptop Keyboard

in particular, the background distribution of dark matter can be reconstructed. Since galaxies are intrinsically elliptical and the weak gravitational lensing signal is small, a very large number of galaxies must be used in these surveys. These weak lensing surveys must carefully avoid a number of important sources of systematic error: the intrinsic shape of galaxies, ASUS X53S Laptop Keyboard

the tendency of a camera's point spread function to distort the shape of a galaxy and the tendency of atmospheric seeing to distort images must be understood and carefully accounted for. The results of these surveys are important for cosmological parameter estimation, to better understand and improve upon the Lambda-CDM model, and to provide a consistency check on other cosmological observations. They may also provide an important future constraint on dark energy.  FUJITSU Lifebook T4220 Laptop Keyboard

3. Microlensing: where no distortion in shape can be seen but the amount of light received from a background object changes in time. The lensing object may be stars in the Milky Way in one typical case, with the background source being stars in a remote galaxy, or, in another case, an even more distant quasar. ASUS F3F Laptop Keyboard

The effect is small, such that (in the case of strong lensing) even a galaxy with a mass more than 100 billion times that of the Sun will produce multiple images separated by only a few arcseconds. Galaxy clusters can produce separations of several arcminutes. In both cases the galaxies and sources are quite distant, many hundreds of megaparsecs away from our Galaxy.  FUJITSU Lifebook T4220 Laptop Keyboard

Gravitational lenses act equally on all kinds of electromagnetic radiation, not just visible light. Weak lensing effects are being studied for the cosmic microwave background as well as galaxy surveys. Strong lenses have been observed inradio and x-ray regimes as well. If a strong lens produces multiple images, there will be a relative time delay between two paths: that is, in one image the lensed object will be observed before the other image. TOSHIBA Satellite L750-ST4N02 Laptop Keyboard

According to general relativity, mass "warps" space–time to create gravitational fields and therefore bend light as a result. This theory was confirmed in 1919 during a solar eclipse, when Arthur Eddington observed the light from starspassing close to the Sun was slightly bent, so that stars appeared slightly out of position. HP 605344-001 Laptop Keyboard

Einstein realized that it was also possible for astronomical objects to bend light, and that under the correct conditions, one would observe multiple images of a single source, called a gravitational lens or sometimes agravitational mirage. HP Pavilion DV7-3065dx Laptop Keyboard

However, as he only considered gravitational lensing by single stars, he concluded that the phenomenon would most likely remain unobserved for the foreseeable future. In 1937, Fritz Zwicky first considered the case where a galaxy could act as a source, something that according to his calculations should be well within the reach of observations. Lenovo 3000 C200 laptop keyboard

It was not until 1979 that the first gravitational lens would be discovered. It became known as the "Twin QSO" since it initially looked like two identical quasistellar objects; it is officially named SBS 0957+561. This gravitational lens was discovered accidentally by Dennis Walsh, Bob Carswell, and Ray Weymann using the Kitt Peak National Observatory 2.1 metertelescope. TOSHIBA Satellite M645-S4070 laptop keyboard

In the 1980s, astronomers realized that the combination of CCD imagers and computers would allow the brightness of millions of stars to be measured each night. In a dense field, such as the galactic center or the Magellanic clouds, many microlensing events per year could potentially be found. This led to efforts such as Optical Gravitational Lensing Experiment, or OGLE, that have characterized hundreds of such events. Packard Bell Easynote TK85 laptop keyboard

Most of the gravitational lenses in the past have been discovered accidentally. A search for gravitational lenses in the northern hemisphere (Cosmic Lens All Sky Survey, CLASS), done in radio frequencies using the Very Large Array (VLA) in New Mexico, led to the discovery of 22 new lensing systems, a major milestone. This has opened a whole new avenue for research ranging from finding very distant objects to finding values for cosmological parameters so we can understand the universe better. HP Pavilion dv6-2124el laptop keyboard

A similar search in the southern hemisphere would be a very good step towards complementing the northern hemisphere search as well as obtaining other objectives for study. If such a search is done using well calibrated and well parameterized instrument and data, a result similar to the northern survey can be expected.  HP 605344-001 laptop keyboard

The use of the Australia Telescope 20 GHz (AT20G) Survey data collected using the Australia Telescope Compact Array (ATCA) stands to be such a collection of data. As the data were collected using the same instrument maintaining a very stringent quality of data we should expect to obtain good results from the search. SONY VAIO VGN-NW250D/W laptop keyboard

The AT20G survey is a blind survey at 20 GHz frequency in the radio domain of the electromagnetic spectrum. Due to the high frequency used, the chances finding gravitational lenses increases as the relative number of compact core objects (e.g. Quasars) are higher (Sadler et al. 2006). This is important as the lensing is easier to detect and identify in simple objects compared to objects with complexity in them.  Packard Bell PEW91 laptop keyboard

This search involves the use of interferometric methods to identify candidates and follow them up at higher resolution to identify them. Full detail of the project is currently under works for publication. SONY VAIO VGN-FS115Z laptop keyboard

In a recent article on Science Daily (Jan. 21 2009) a team of scientists led by a cosmologist from the U.S. Department of Energy's Lawrence Berkeley National Laboratory has made major progress in extending the use of gravitational lensing to the study of much older and smaller structures than was previously possible by stating that weak gravitational lensing improves measurements of distant galaxies.[4] TOSHIBA Satellite L675-S7044 laptop keyboard

Kaiser et al. (1995), Luppino & Kaiser (1997) and Hoekstra et al. (1998) prescribed a method to invert the effects of the Point Spread Function (PSF) smearing and shearing, recovering a shear estimator uncontaminated by the systematic distortion of the PSF. This method (KSB+) is the most widely used method in current weak lensing shear measurements. HP G42-466LA laptop keyboard

Galaxies have random rotations and inclinations. As a result, the shear effects in weak lensing need to be determined by statistically preferred orientations. The primary source of error in lensing measurement is due to the convolution of the PSF with the lensed image. The KSB method measures the ellipticity of a galaxy image. SONY VAIO VGN-FS415M laptop keyboard

The objects in lensed images are parameterized according to their weighted quadrupole moments. For a perfect ellipse, the weighted quadrupole moments are related to the weighted ellipticity. KSB calculate how a weighted ellipticity measure is related to the shear and use the same formalism to remove the effects of the PSF. COMPAQ Presario CQ50-106CA laptop keyboard

KSB’s primary advantages are its mathematical ease and relatively simple implementation. However, KSB is based on a key assumption that the PSF is circular with an anisotropic distortion. It’s fine for current cosmic shear surveys, but the next generation of surveys (e.g. LSST) may need much better accuracy than KSB can provide. Because during that time, the statistical errors from the data are negligible, the systematic errors will dominate. SONY VAIO VGN-FS415M laptop keyboard

imaged quasar, meaning that an intervening mass concentration between Earth and the quasar bends light so that two images of the quasar appear in the sky. This is known as gravitational lensing, and is a consequence of Einsteinian warped space-time. The quasar lies at redshift z = 1.41 (8.7 billion ly), while the lensing galaxy lies at redshift z = 0.355 (3.7 billion ly) ACER Aspire 5810TZ-4657 laptop keyboard

. The lensing galaxy with apparent dimension of 0.42×0.22 arcminuteslies almost in line with the B image, lying 1 arcsecond off. The quasar lies 10 arcminutes north of NGC 3079, in the constellation Ursa Major. The astronomical data services SIMBAD and NASA/IPAC Extragalactic Database (NED) list several other names for this system.  HP HDX18-1050EB laptop keyboard

The Twin Quasar's two images are separated by 6 arcseconds. Both images have an apparent magnitude of 17, with the A component having 16.7 and the B component having 16.5. There is a 417 ± 3 day time lag between the two images.[1]

SONY VAIO VGN-N11S laptop keyboard

The team noticed that the two quasars were unusually close to each other, and that their redshift and visible light spectrum were surprisingly similar. They published their suggestion of "the possibility that they are two images of the same object formed by a gravitational lens".[3]

The Twin Quasar was one of the first directly observable effects of gravitational lensing, which was first described in 1936 by Albert Einstein in his General Theory of Relativity.[4] DELL NSK-DD101 laptop keyboard

Critics however identified a difference in appearance between the two quasars in radio frequency images. In mid 1979 a team led by David Roberts at the VLA(Very Large Array) near Socorro, New Mexico/USA discovered a relativistic jet emerging from quasar A with no corresponding equivalent in quasar B.[5]Furthermore, the distance between the two images, 6 arcseconds, was too great to have been produced by the gravitational effect of the galaxy G1, a galaxy identified near quasar B.  Compaq Mini 730EA laptop keyboard

Young et al. discovered that galaxy G1 is part of a galaxy cluster which increases the gravitational deflection and can explain the observed distance between the images.[6] Finally, a team led by Marc V. Gorenstein observed essentially identical relativistic jets on very small scales from both A and B in 1983 usingVLBI (Very Long Baseline Interferometry).[7]  SONY VGN-FE48E laptop keyboard

The difference between the large-scale radio images is attributed to the special geometry needed for gravitational lensing, which is satisfied by the quasar but not by all of the extended jet emission seen by the VLA near image A. SONY VAIO VGN-AR320E laptop keyboard

Slight spectral differences between quasar A and quasar B can be explained by different densities of the intergalactic medium in the light paths, resulting in differing extinction.[8]

30 years of observation made it clear that image A of the quasar reaches earth about 14 months earlier than the corresponding image B, resulting in a difference of path length of 1.1 ly.  Packard Bell Easynote TK85 laptop keyboard

In 1996 a team at Harvard-Smithsonian Center for Astrophysics led by Rudy E. Schild discovered an anomalous fluctuation in one image's lightcurve, which led to a controversial and unconfirmable theory that there is a planet approximately three Earth masses in size in the lensing galaxy. HP Pavilion dv6-3015tx laptop keyboard

The results remain speculative because the chance alignment that led to its discovery will never happen again. If it could be confirmed, however, it would make it the most distant known planet, 4 billion ly away.[9] HP Pavilion dv6-2070eo laptop keyboard

In 2006, R. E. Schild suggested that the accreting object at the heart of Q0957+561 is not a supermassive black hole, as is generally believed for all quasars, but a magnetospheric eternally collapsing object. Schild's team at the Harvard-Smithsonian Center for Astrophysics asserted that "this quasar appears to be dynamically dominated by a magnetic field internally anchored to its central, rotating supermassive compact object" (R. E. Schild).[10] HP Mini 110-1036TU laptop keyboard

Kitt Peak was selected by its first director, Aden B. Meinel, in 1958 as the site for a national observatory under contract with the National Science Foundation (NSF) and was administered by the Association of Universities for Research in Astronomy. The land was leased from the Tohono O'odham under a perpetual agreement. SONY VAIO VGN-NW11S/S laptop keyboard

The second director (1960 to 1971) was Nicholas U. Mayall. In 1982 NOAO was formed to consolidate the management of three optical observatories — Kitt Peak; the National Solar Observatory facilities at Kitt Peak and Sacramento Peak, New Mexico; and the Cerro Tololo Inter-American Observatory in Chile. HP Pavilion dv5-1026eo laptop keyboard

The observatory sites are under lease from the Tohono O'odham Nation at the amount of a quarter dollar per acre yearly, which was overwhelmingly approved by the Council in the 1950s. In 2005, the Tohono O'odham Nation brought suit against the National Science Foundation to stop further construction of gamma ray detectors in the Gardens of the Sacred Tohono O'odham Spirit I'itoi, which are just below the summit.[2] HP Mini 110-1140TU laptop keyboard

The principal instruments at KPNO are the Mayall 4 metre telescope; the WIYN 3.5 metre telescope; and further 2.1 m, 1.3 m, 0.9 m, and 0.4 m reflecting telescopes. The McMath-Pierce Solar Telescope on the facilities is the largest solar telescope in the world and the largest unobstructed reflector (it doesn't have a secondary mirror in the path of incoming light). The ARO 12m Radio Telescope is also in the location. HP Mini 210 laptop keyboard

In physics, spacetime (also space–time, space time or space–time continuum) is any mathematical model that combines space and time into a single continuum. Spacetime is usually interpreted with space as existing in three dimensions and time playing the role of a fourth dimension that is of a different sort from the spatial dimensions. ASUS X53S laptop keyboard

From a Euclidean space perspective, the universe has three dimensions of space and one of time. By combining space and time into a single manifold, physicists have significantly simplified a large number of physical theories, as well as described in a more uniform way the workings of the universe at both the supergalactic and subatomic levels. HP 633183-001 laptop keyboard

In non-relativistic classical mechanics, the use of Euclidean space instead of spacetime is appropriate, as time is treated as universal and constant, being independent of the state of motion of an observer. In relativistic contexts, time cannot be separated from the three dimensions of space, because the observed rate at which time passes for an object depends on the object's velocity relative to the observer and also on the strength of gravitational fields, which can slow the passage of time. ACER NSK-H3M1D laptop keyboard

In cosmology, the concept of spacetime combines space and time to a single abstract universe. Mathematically it is amanifold consisting of "events" which are described by some type of coordinate system. Typically three spatial dimensions (length, width, height), and one temporal dimension (time) are required.  ACER Extensa 5235 laptop keyboard

Dimensions are independent components of a coordinate grid needed to locate a point in a certain defined "space". For example, on the globe the latitude andlongitude are two independent coordinates which together uniquely determine a location. In spacetime, a coordinate grid that spans the 3+1 dimensions locates events (rather than just points in space), i.e. time is added as another dimension to the coordinate grid.  Lenovo 45N2071 laptop keyboard

This way the coordinates specify where and when events occur. However, the unified nature of spacetime and the freedom of coordinate choice it allows imply that to express the temporal coordinate in one coordinate system requires both temporal and spatial coordinates in another coordinate system. Unlike in normal spatial coordinates,  Packard Bell Easynote TK85 laptop keyboard

there are still restrictions for how measurements can be made spatially and temporally (see Spacetime intervals). These restrictions correspond roughly to a particular mathematical model which differs from Euclidean space in its manifestsymmetry. HP Pavilion dv6-2030ev laptop keyboard

Until the beginning of the 20th century, time was believed to be independent of motion, progressing at a fixed rate in all reference frames; however, later experiments revealed that time slows at higher speeds of the reference frame relative to another reference frame. Such slowing, called time dilation, is explained in special relativity theory. Many experiments have confirmed time dilation, ACER Aspire 3623WXMi laptop keyboard

such as the relativistic decay of muons from cosmic ray showers and the slowing of atomic clocks aboard a Space Shuttle relative to synchronized Earth-bound inertial clocks. The duration of time can therefore vary according to events and reference frames.

When dimensions are understood as mere components of the grid system, rather than physical attributes of space, it is easier to understand the alternate dimensional views as being simply the result of coordinate transformations.  TOSHIBA NB100 laptop keyboard

The term spacetime has taken on a generalized meaning beyond treating spacetime events with the normal 3+1 dimensions. It is really the combination of space and time. Other proposed spacetime theories include additional dimensions—normally spatial but there exist some speculative theories that include additional temporal dimensions and even some that include dimensions that are neither temporal nor spatial (e.g. superspace). SONY KFRMBA220A laptop keyboard

How many dimensions are needed to describe the universe is still an open question. Speculative theories such as string theory predict 10 or 26 dimensions (with M-theorypredicting 11 dimensions: 10 spatial and 1 temporal), but the existence of more than four dimensions would only appear to make a difference at the subatomiclevel.[1] SONY VAIO VGN-N38Z/W laptop keyboard

Arthur Schopenhauer wrote in §18 of On the Fourfold Root of the Principle of Sufficient Reason (1813): "...the representation of coexistence is impossible in Time alone; it depends, for its completion, upon the representation of Space; because, in mere Time, all things follow one another, and in mere Space all things are side by side; it is accordingly only by the combination of Time and Space that the representation of coexistence arises."  HP 576835-001 laptop keyboard

The idea of a unified spacetime is stated by Edgar Allan Poe in his essay on cosmology titled Eureka (1848) that "Space and duration are one." In 1895, in his novel The Time Machine, H.G. Wells wrote, "There is no difference between time and any of the three dimensions of space except that our consciousness moves along it", and that "any real body must have extension in four directions: it must have Length, Breadth, Thickness, and Duration." TOSHIBA Satellite L355-S7905 laptop keyboard

Marcel Proust, in his novel Swann's Way (published 1913), describes the village church of his childhood's Combray as "... a building which occupied, so to speak, four dimensions of space—the name of the fourth being Time..."  DELL AEGM7U00110 laptop keyboard

Partager cet article

Repost 0
Published by batterys
commenter cet article