What Is the Most Distant Object That Frank Can Focus on While Wearing This Older Pair of Glasses?

Light bending by mass between source and observer

A light source passes backside a gravitational lens (point mass placed in the middle of the prototype). The aqua circle is the light source equally it would be seen if there were no lens, while white spots are the multiple images of the source (see Einstein band).

A gravitational lens is a distribution of affair (such as a cluster of galaxies) between a distant lite source and an observer, that is capable of bending the calorie-free from the source as the light travels toward the observer. This effect is known as gravitational lensing, and the amount of bending is one of the predictions of Albert Einstein's general theory of relativity.^{[i] [2]} Treating light every bit corpuscles travelling at the speed of light, Newtonian physics too predicts the bending of light, but only half of that predicted past general relativity.^{[iii] [iv] [5] [6]}

Although Einstein made unpublished calculations on the subject in 1912,^[7] Orest Khvolson (1924)^[8] and Frantisek Link (1936)^[9] are by and large credited with being the showtime to discuss the issue in print. However, this effect is more normally associated with Einstein, who published an article on the discipline in 1936.^[10]

Fritz Zwicky posited in 1937 that the result could allow galaxy clusters to deed equally gravitational lenses. Information technology was not until 1979 that this effect was confirmed by observation of the so-called Twin QSO SBS 0957+561.

Description [edit]

Gravitational lensing – intervening galaxy modifies advent of a galaxy far backside it (video; artist's concept).

This schematic image shows how calorie-free from a distant galaxy is distorted by the gravitational effects of a foreground galaxy, which acts like a lens and makes the distant source appear distorted, merely magnified, forming feature rings of light, known as Einstein rings.

An analysis of the baloney of SDP.81 acquired by this event has revealed star-forming clumps of matter.

Unlike an optical lens, a betoken-like gravitational lens produces a maximum deflection of light that passes closest to its middle, and a minimum deflection of lite that travels furthest from its center. Consequently, a gravitational lens has no unmarried focal signal, merely a focal line. The term "lens" in the context of gravitational light deflection was first used past O.J. Lodge, who remarked that it is "not permissible to say that the solar gravitational field acts like a lens, for it has no focal length".^{[11] [ page needed ]} If the (light) source, the massive lensing object, and the observer lie in a straight line, the original calorie-free source volition appear as a band around the massive lensing object (provided the lens has circular symmetry). If there is whatever misalignment, the observer volition meet an arc segment instead. This phenomenon was first mentioned in 1924 by the St. Petersburg physicist Orest Khvolson,^[12] and quantified by Albert Einstein in 1936. It is normally referred to in the literature every bit an Einstein band, since Khvolson did not business organization himself with the flux or radius of the ring image. More normally, where the lensing mass is complex (such as a galaxy group or cluster) and does non cause a spherical baloney of spacetime, 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.

There are three classes of gravitational lensing:^{[xi] [ page needed ] [13]}

Strong lensing

Where at that place are hands visible distortions such equally the formation of Einstein rings, arcs, and multiple images. Despite being considered "stiff", the effect is in general relatively small, such that even a galaxy with a mass more 100 billion times that of the Lord's day will produce multiple images separated by just 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.

Weak lensing

Where the distortions of background sources are much smaller and tin only be detected by analyzing large numbers of sources in a statistical style to discover coherent distortions of only a few percent. The lensing shows up statistically as a preferred stretching of the background objects perpendicular to the management to the centre of the lens. By measuring the shapes and orientations of large numbers of distant galaxies, their orientations tin can exist averaged to measure the shear of the lensing field in any region. This, in turn, can exist used to reconstruct the mass distribution in the area: in particular, the background distribution of dark affair 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, the trend of a camera'south signal spread function to distort the shape of a milky way and the trend of atmospheric seeing to distort images must be understood and advisedly accounted for. The results of these surveys are of import for cosmological parameter estimation, to better sympathise and better upon the Lambda-CDM model, and to provide a consistency check on other cosmological observations. They may as well provide an important future constraint on dark energy.

Microlensing

Where no distortion in shape tin can be seen but the amount of low-cal received from a groundwork object changes in fourth dimension. The lensing object may be stars in the Milky way in one typical example, with the background source existence stars in a remote milky way, or, in another case, an fifty-fifty more distant quasar. In extreme cases, a star in a afar galaxy tin can human action equally a microlens and magnify some other star much farther away. The first example of this was the star MACS J1149 Lensed Star 1 (also known as Icarus), that is to date the farthest star e'er observed, thank you to the boost in flux due to the microlensing effect.

Gravitational lenses act equally on all kinds of electromagnetic radiation, not only visible light, and also in not-electromagnetic radiation, like gravitational waves. Weak lensing effects are beingness studied for the catholic microwave background as well as milky way surveys. Stiff lenses have been observed in radio and 10-ray regimes as well. If a strong lens produces multiple images, in that location will be a relative time delay between 2 paths: that is, in one epitome the lensed object will exist observed before the other image.

History [edit]

One of Eddington's photographs of the 1919 solar eclipse experiment, presented in his 1920 paper announcing its success

Henry Cavendish in 1784 (in an unpublished manuscript) and Johann Georg von Soldner in 1801 (published in 1804) had pointed out that Newtonian gravity predicts that starlight will curve effectually a massive object^[xiv] as had already been supposed by Isaac Newton in 1704 in his Queries No.one in his book Opticks.^[15] The same value as Soldner'due south was calculated by Einstein in 1911 based on the equivalence principle alone.^{[11] [ folio needed ]} Withal, Einstein noted in 1915, in the process of completing general relativity, that his (and thus Soldner'southward) 1911-result is simply one-half of the correct value. Einstein became the offset to calculate the correct value for calorie-free angle.^[xvi]

The showtime observation of light deflection was performed by noting the modify in position of stars as they passed near the Sunday on the celestial sphere. The observations were performed in 1919 by Arthur Eddington, Frank Watson Dyson, and their collaborators during the total solar eclipse on May 29.^[17] The solar eclipse allowed the stars about the Sun to be observed. Observations were fabricated simultaneously in the cities of Sobral, Ceará, Brazil and in São Tomé and Príncipe on the west coast of Africa.^[18] The observations demonstrated that the light from stars passing close to the Sunday was slightly bent, and so that stars appeared slightly out of position.^[19]

Bending lite around a massive object from a afar source. The orange arrows show the apparent position of the background source. The white arrows show the path of the low-cal from the true position of the source.

In the formation known as Einstein's Cross, 4 images of the same afar quasar appear around a foreground galaxy due to strong gravitational lensing.

The result was considered spectacular news and made the front page of virtually major newspapers. It made Einstein and his theory of full general relativity world-famous. When asked by his assistant what his reaction would accept been if general relativity had not been confirmed by Eddington and Dyson in 1919, Einstein said "So I would experience sorry for the dear Lord. The theory is correct anyway."^[20] In 1912, Einstein had speculated that an observer could see multiple images of a single lite source, if the light were deflected around a mass. This issue would make the mass act as a kind of gravitational lens. However, every bit he only considered the effect of deflection effectually a unmarried star, he seemed to conclude that the phenomenon was unlikely to exist observed for the foreseeable time to come since the necessary alignments betwixt stars and observer would be highly improbable. Several other physicists speculated nearly gravitational lensing as well, only all reached the aforementioned conclusion that it would be nearly impossible to notice.^[10]

Although Einstein made unpublished calculations on the subject field,^[7] the first discussion of the gravitational lens in print was past Khvolson, in a brusque commodity discussing the "halo effect" of gravitation when the source, lens, and observer are in about-perfect alignment,^[8] at present referred to as the Einstein ring.

In 1936, subsequently some urging by Rudi Due west. Mandl, Einstein reluctantly published the short commodity "Lens-Like Action of a Star By the Difference of Light In the Gravitational Field" in the journal Science.^[10]

In 1937, Fritz Zwicky offset considered the case where the newly discovered galaxies (which were called 'nebulae' at the time) could act as both source and lens, and that, considering of the mass and sizes involved, the event was much more likely to be observed.^[21]

In 1963 Yu. G. Klimov, Southward. Liebes, and Sjur Refsdal recognized independently that quasars are an ideal light source for the gravitational lens effect.^[22]

It was non until 1979 that the first gravitational lens would be discovered. Information technology 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 by Dennis Walsh, Bob Carswell, and Ray Weymann using the Kitt Peak National Observatory two.1 meter telescope.^[23]

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 equally the galactic center or the Magellanic clouds, many microlensing events per year could potentially be establish. This led to efforts such equally Optical Gravitational Lensing Experiment, or OGLE, that have characterized hundreds of such events, including those of OGLE-2016-BLG-1190Lb and OGLE-2016-BLG-1195Lb.

Caption in terms of spacetime curvature [edit]

False gravitational lensing (black hole passing in front of a background galaxy).

In general relativity, light follows the curvature of spacetime, hence when low-cal passes around a massive object, it is aptitude. This means that the light from an object on the other side will be bent towards an observer's eye, but like an ordinary lens. In general relativity the speed of lite depends on the gravitational potential (i.eastward. the metric) and this bending tin can be viewed as a upshot of the light traveling along a slope in low-cal speed. Light rays are the boundary betwixt the future, the spacelike, and the by regions. The gravitational attraction tin be viewed as the motion of undisturbed objects in a background curved geometry or alternatively as the response of objects to a force in a apartment geometry. The angle of deflection is:

${\displaystyle \theta ={\frac {4GM}{rc^{2}}}}$

toward the mass M at a distance r from the affected radiation, where G is the universal constant of gravitation and c is the speed of light in a vacuum.

Since the Schwarzschild radius ${\displaystyle r_{\text{southward}}}$ is defined every bit ${\displaystyle r_{\text{southward}}={2Gm}/{c^{2}}}$ and escape velocity ${\displaystyle v_{\text{e}}}$ is divers equally ${\textstyle v_{\text{east}}={\sqrt {2Gm/r}}=\beta _{\text{e}}c}$ , this can also be expressed in elementary course as

${\displaystyle \theta =2{\frac {r_{\text{s}}}{r}}=2\left({\frac {v_{\text{due east}}}{c}}\right)^{2}=2\beta _{\text{e}}^{ii}}$

Search for gravitational lenses [edit]

This image from the NASA/ESA Hubble Infinite Telescope shows the galaxy cluster MACS J1206.

Most of the gravitational lenses in the past have been discovered accidentally. A search for gravitational lenses in the northern hemisphere (Cosmic Lens All Heaven Survey, Class), washed in radio frequencies using the Very Large Array (VLA) in New United mexican states, led to the discovery of 22 new lensing systems, a major milestone. This has opened a whole new artery for research ranging from finding very distant objects to finding values for cosmological parameters so we can understand the universe meliorate.

A similar search in the southern hemisphere would be a very skilful pace 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 musical instrument and data, a event similar to the northern survey can be expected. The use of the Australia Telescope xx 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 await to obtain good results from the search. 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 of finding gravitational lenses increases as the relative number of compact core objects (e.g. quasars) are higher (Sadler et al. 2006). This is important equally the lensing is easier to detect and identify in unproblematic objects compared to objects with complexity in them. This search involves the use of interferometric methods to identify candidates and follow them upwardly at higher resolution to place them. Full detail of the project is currently under works for publication.

Milky way cluster SDSS J0915+3826 helps astronomers to study star formation in galaxies.^[24]

Microlensing techniques take been used to search for planets exterior our solar system. A statistical analysis of specific cases of observed microlensing over the time period of 2002 to 2007 found that most stars in the Milky way galaxy hosted at least i orbiting planet within 0.5 to 10 AUs.^[25]

In 2009, weak gravitational lensing was used to extend the mass-10-ray-luminosity relation to older and smaller structures than was previously possible to improve measurements of afar galaxies.^[26]

As of 2013^[update] the most afar gravitational lens milky way, J1000+0221, had been found using NASA'southward Hubble Space Telescope.^{[27] [28]} While it remains the most afar quad-image lensing galaxy known, an even more than distant two-prototype lensing galaxy was subsequently discovered by an international team of astronomers using a combination of Hubble Space Telescope and Keck telescope imaging and spectroscopy. The discovery and analysis of the IRC 0218 lens was published in the Astrophysical Journal Messages on June 23, 2014.^[29]

Inquiry published Sep 30, 2013 in the online edition of Physical Review Letters, led past McGill University in Montreal, Québec, Canada, has discovered the B-modes, that are formed due to gravitational lensing effect, using National Scientific discipline Foundation's South Pole Telescope and with assistance from the Herschel space observatory. This discovery would open up the possibilities of testing the theories of how our universe originated.^{[30] [31]}

Solar gravitational lens [edit]

Albert Einstein predicted in 1936 that rays of lite from the same direction that skirt the edges of the Lord's day would converge to a focal point approximately 542 AUs from the Sun.^[34] Thus, a probe positioned at this distance (or greater) from the Lord's day could use the Lord's day as a gravitational lens for magnifying distant objects on the reverse side of the Sun.^[35] A probe'southward location could shift around equally needed to select different targets relative to the Sunday.

This distance is far beyond the progress and equipment capabilities of infinite probes such as Voyager 1, and beyond the known planets and dwarf planets, though over thousands of years 90377 Sedna will move further away on its highly elliptical orbit. The high proceeds for potentially detecting signals through this lens, such every bit microwaves at the 21-cm hydrogen line, led to the suggestion by Frank Drake in the early days of SETI that a probe could be sent to this distance. A multipurpose probe SETISAIL and afterward FOCAL was proposed to the ESA in 1993, but is expected to exist a difficult task.^[36] If a probe does pass 542 AU, magnification capabilities of the lens will go on to act at further distances, as the rays that come to a focus at larger distances pass further away from the distortions of the Sunday'southward corona.^[37] A critique of the concept was given by Landis,^[38] who discussed issues including interference of the solar corona, the high magnification of the target, which will make the design of the mission focal plane hard, and an analysis of the inherent spherical abnormality of the lens.

In 2020, NASA physicist Slava Turyshev presented his idea of Direct Multipixel Imaging and Spectroscopy of an Exoplanet with a Solar Gravitational Lens Mission. The lens could reconstruct the exoplanet image with ~25 km-calibration surface resolution, enough to see surface features and signs of habitability.^[39]

Measuring weak lensing [edit]

Galaxy cluster MACS J2129-0741 and lensed milky way MACS2129-1.^[forty]

Kaiser, Squires and Broadhurst (1995),^[41] Luppino & Kaiser (1997)^[42] and Hoekstra et al. (1998) prescribed a method to invert the furnishings 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 near widely used method in weak lensing shear measurements.^{[43] [44]}

Galaxies take random rotations and inclinations. Every bit a upshot, the shear effects in weak lensing demand to be determined past statistically preferred orientations. The primary source of mistake 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. The shear is proportional to the ellipticity. 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 employ the aforementioned formalism to remove the effects of the PSF.^[45]

KSB's primary advantages are its mathematical ease and relatively simple implementation. However, KSB is based on a key assumption that the PSF is round with an anisotropic distortion. This is a reasonable assumption for catholic shear surveys, merely the next generation of surveys (e.g. LSST) may demand much meliorate accuracy than KSB can provide.

Gallery [edit]

• 

  Sunburst Arc galaxy.^[46]

• 

  Gravitationally lensed Quasar.^[47]

• 

  In SDSS J0952+3434, the lower arc-shaped milky way has the characteristic shape of a milky way that has been gravitationally lensed.^[48]

• 

  Warped and distorted around SDSS J1050+0017.^[49]

• 

  Galaxy SPT0615-JD existed when the Universe was just 500 million years quondam.^[l]

• 

  Gravitational lenses found in the DESI Legacy Survey data^[51]

• 

  Gravitational lenses found in the DESI Legacy Survey information^[52]

• 

  The lensing phenomenon allows for features as minor every bit about 100 light-years or less.^[53]

• 

  Gravitational lens discovered at redshift z = 1.53.^[56]

• 

  Gravitational Lensing Graphic (Jan eight, 2020)

• 

  Hubble Showcases Hamilton's Object

Gravitationally-lensed distant star-forming galaxies.^[57]

Meet also [edit]

• Terrestrial atmospheric lens
• Gravitational lensing formalism
• Stiff gravitational lensing
  • Einstein cross
  • Einstein band
• Weak gravitational lensing
• Gravitational microlensing
• SN Refsdal
• Euclid (spacecraft), to measure gravitational lensing

Historical papers and references [edit]

• Khvolson, O (1924). "Über eine mögliche Form fiktiver Doppelsterne". Astronomische Nachrichten. 221 (20): 329–330. Bibcode:1924AN....221..329C. doi:ten.1002/asna.19242212003.
• Einstein, Albert (1936). "Lens-like Action of a Star by the Deviation of Light in the Gravitational Field". Science. 84 (2188): 506–7. Bibcode:1936Sci....84..506E. doi:10.1126/science.84.2188.506. JSTOR 1663250. PMID 17769014. S2CID 38450435.
• Renn, Jürgen; Tilman Sauer; John Stachel (1997). "The Origin of Gravitational Lensing: A Postscript to Einstein's 1936 Science newspaper". Science. 275 (5297): 184–6. Bibcode:1997Sci...275..184R. doi:ten.1126/science.275.5297.184. PMID 8985006. S2CID 43449111.

References [edit]

Notes

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5. ^ Gabor Kunstatter; Jeffrey M Williams; D E Vincent (1992). Full general Relativity And Relativistic Astrophysics - Proceedings Of The 4th Canadian Conference. Globe Scientific. p. 100. ISBN978-981-4554-87-9. Extract of page 100
6. ^ Pekka Teerikorpi; Mauri Valtonen; K. Lehto; Harry Lehto; Gene Byrd; Arthur Chernin (2008). The Evolving Universe and the Origin of Life: The Search for Our Catholic Roots (illustrated ed.). Springer Science & Business organization Media. p. 165. ISBN978-0-387-09534-9. Extract of page 165
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Bibliography

• "Accidental Astrophysicists". Science News, June thirteen, 2008.
• "XFGLenses". A Calculator Program to visualize Gravitational Lenses, Francisco Frutos-Alfaro
• "G-LenS". A Point Mass Gravitational Lens Simulation, Marker Boughen.
• Newbury, Pete, "Gravitational Lensing". Institute of Applied Mathematics, The University of British Columbia.
• Cohen, N., "Gravity's Lens: Views of the New Cosmology", Wiley and Sons, 1988.
• "Q0957+561 Gravitational Lens". Harvard.edu.
• Bridges, Andrew, "Well-nigh distant known object in universe discovered". Associated Press. February 15, 2004. (Uttermost galaxy found by gravitational lensing, using Abell 2218 and Hubble Infinite Telescope.)
• Analyzing Corporations ... and the Creation An unusual career path in gravitational lensing.
• "HST images of potent gravitational lenses". Harvard-Smithsonian Center for Astrophysics.
• "A planetary microlensing event" and "A Jovian-mass Planet in Microlensing Event OGLE-2005-BLG-071", the commencement extra-solar planet detections using microlensing.
• Gravitational lensing on arxiv.org
• NRAO Class home page
• AT20G survey
• A diffraction limit on the gravitational lens consequence (Bontz, R. J. and Haugan, M. P. "Astrophysics and Space Scientific discipline" vol. 78, no. 1, p. 199-210. August 1981)

Farther reading

• Blandford & Narayan; Narayan, R (1992). "Cosmological applications of gravitational lensing". Annual Review of Astronomy and Astrophysics. 30 (1): 311–358. Bibcode:1992ARA&A..xxx..311B. doi:10.1146/annurev.aa.thirty.090192.001523.
• Matthias Bartelmann; Peter Schneider (2000-08-17). "Weak Gravitational Lensing" (PDF). Archived from the original (PDF) on 2007-02-26.
• Khavinson, Dmitry; Neumann, Genevra (June–July 2008). "From Primal Theorem of Algebra to Astrophysics: A "Harmonious" Path" (PDF). Notices of the AMS. 55 (half-dozen): 666–675. .
• Petters, Arlie O.; Levine, Harold; Wambsganss, Joachim (2001). Singularity Theory and Gravitational Lensing. Progress in Mathematical Physics. Vol. 21. Birkhäuser.
• Tools for the evaluation of the possibilities of using parallax measurements of gravitationally lensed sources (Stein Vidar Hagfors Haugan. June 2008)

External links [edit]

• Video: Evalyn Gates – Einstein's Telescope: The Search for Dark Matter and Dark Energy in the Universe Archived 2018-09-02 at the Wayback Machine, presentation in Portland, Oregon, on April xix, 2009, from the writer'southward recent book bout.
• Audio: Fraser Cain and Dr. Pamela Gay – Astronomy Cast: Gravitational Lensing, May 2007

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Source: https://en.wikipedia.org/wiki/Gravitational_lens

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