# gravitational lensing explained

The term 'gravitational lensing' refers to the bending of light rays due to the gravitational influence of the massive body. Explained: What is gravitational lensing? These weak lensing surveys must carefully avoid a number of important sources of systematic error: the intrinsic shape of galaxies, 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. 2 While those galaxies are generally too faint to be easily seen, gravitational lensing makes them visible, transmitting information across billions of light-years for astronomers to study. Gravitational Lensing and Its Types.The concept of Gravitational lensing is originated from the Einstein General theory of relativity in which Einstein stated that heavy objects distort spacetime and if light passes near to those objects then it would bend, and this phenomenon is known as bending of light due to gravity. A gravitational field of a very massive object, such as a planet, star, or galaxy, or galaxy cluster, or even a black hole, pulls more strongly at objects in nearby space. 2 Well,gravity’s a funny thing. Galaxy cluster Abell 383 is a gravitational lens. )[3] So there seems to be a degeneracy. [1][2] (Classical physics also predicts the bending of light, but only half of that predicted by general relativity. 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. This ’gravitational lens’ bends and magniﬁes the light of galaxies located far behind it, distorting their shapes and creating multiple images of individual galaxies. As such, the causality was the existence of extremely massive areas within the cluster which would be able to account for a gravitational lens. Weak lensing: where the distortions of background sources are much smaller and can only be detected by analyzing large numbers of sources in a statistical way to find coherent distortions of only a few percent. BODY Although the gravitational lensing of light is well known, the most promising focusing agents (i.e., the concentrated masses often located at the centers of galaxies) tend to block the focused light with clouds of dust and also tend to emit in-band "noise" that often dominates any desired focused signal. Gravitational lensing and how it works. {\displaystyle v_{\mathrm {e} }={\sqrt {2Gm/r}}=\beta _{e}c} {\displaystyle r_{\mathrm {s} }={2Gm}/{c^{2}}} 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. Gravitational lensing also allows us to observe invisible things in our Universe. A gravitational lens is formed when the light from a very distant, bright object (such as a quasar) is "bent" around a massive object (such as a massive galaxy) between the bright object and the viewer.The process is known as gravitational lensing, and was one of the predictions made by … The idea of gravitational lensing was first suggested in Einstein's Theory of General Relativity. In our everyday lives, we think of it as a force. Gravitational lensing occurs to all wavelengths of light, from radio and infrared to visible and ultraviolet, which makes sense, since they're all part of the spectrum of electromagnetic radiation that bathes the universe. Their intense gravity also lenses light, as shown in this simulation using an HST image of the sky to demonstrate. §1. They also reveal the existence of planets around distant stars. This formula is identical to the formula for weak gravitational lensing derived using relativistic Newtonian dynamics [21] without curving spacetime. That tells astronomers that microlensing was likely involved. A multipurpose probe SETISAIL and later FOCAL was proposed to the ESA in 1993, but is expected to be a difficult task. 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. Not only does it tug away at you, me, planets, moons and stars, but it can even bend light itself. This is works in a way analogous to a lens (and hence the name). The concept behind gravitational lensing is simple: everything in the universe has mass and that mass has a gravitational pull. Light rays are the boundary between the future, the spacelike, and the past regions. Einstein predicted that the gravitational field of any massive star will act as a gravitational lens and bend the path followed by the light rays originating from any bright star that happens to pass behind the lens. By definition, everything in the universe can act like a gravitational lens; your observational technique just has to be sensitive enough to detect the lensing. G. Klimov, S. Liebes, and Sjur Refsdal recognized independently that quasars are an ideal light source for the gravitational lens effect. is defined as This was the gravitational lensing revolution in astrophysics. The KSB method measures the ellipticity of a galaxy image. The observations were performed in 1919 by Arthur Eddington, Frank Watson Dyson, and their collaborators during the total solar eclipse on May 29. While gravitational lensing has existed throughout history, it's fairly safe to say that it was first discovered in the early 1900s. and escape velocity It can create the appearance of two or more objects where there is really only one. [25][26] While it remains the most distant quad-image lensing galaxy known, an even more distant two-image lensing galaxy was subsequently discovered by an international team of astronomers using a combination of Hubble Space Telescope and Keck telescope imaging and spectroscopy. In both cases the galaxies and sources are quite distant, many hundreds of megaparsecs away from our Galaxy. Astronomers use those shapes to determine the distribution of mass in the galaxy clusters doing the lensing or to figure out their distribution of dark matter. On the chance occasion when the distant source, the lensing object, and telescopes on Earth all line up, astronomers are able to see a ring of light. The bigger the mass of an object the stronger its gravitational pull and the stronger it affects its environment. Rosenthal-Schneider, Ilse: Reality and Scientific Truth. The light from the object gets bent round the massive body in between. Although lensing has been around as a theory since Chwolson’s mention of it in 1924, it wasn’t “confirmed” until … Strong lenses have been observed in radio and x-ray regimes as well. In 1936, after some urging by Rudi W. Mandl, Einstein reluctantly published the short article "Lens-Like Action of a Star By the Deviation of Light In the Gravitational Field" in the journal Science. In gravitational lensing, it is common to distinguish between macrolensing and microlensing. The angle of deflection is: 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. NASA, ESA, and D. Coe, J. Anderson, and R. van der Marel (Space Telescope Science Institute), Science Credit: NASA, ESA, C.-P. Ma (University of California, Berkeley), and J. Thomas (Max Planck Institute for Extraterrestrial Physics, Garching, Germany). This, in turn, can be used to reconstruct the mass distribution in the area: in particular, the background distribution of dark matter can be reconstructed. v This is also the only method of hunting for exoplanets outside our own galaxy. [8] However, Einstein noted in 1915, in the process of completing general relativity, that his (and thus Soldner's) 1911-result is only half of the correct value. After careful observations using the Kitt Peak National Observatory in Arizona, astronomers were able to figure out that there weren't two identical quasars (distant very active galaxies) near each other in space. 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. They may also provide an important future constraint on dark energy. Gravitational lens discovered at redshift z = 1.53. If a planet is positioned close enough to the lensing star so that it crosses one of the two light streams emanating from the source star, the planet's own gravity bends the light stream and temporarily produces a third image of the source star. 12 Iconic Images From Hubble Space Telescope, Ghost Light from Dead Galaxies Sheds Light on Ancient Galaxy Interactions, Learn About the True Speed of Light and How It's Used, Astronomers Peer Deep into Blobs in Space, Hubble Space Telescope: On the Job Since 1990, Gemini Observatory Provides Complete Coverage of the Sky, M.S., Journalism and Mass Communications, University of Colorado - Boulder. This search involves the use of interferometric methods to identify candidates and follow them up at higher resolution to identify them. The Optical Gravitational Lensing Experiment (OGLE), led by Andrzej Udalski of Warsaw University, found the first 3 planets ever detected through microlensing. It became known as the "Twin QSO" since it initially looked like two identical quasistellar objects. Well,gravity’s a funny thing. glass) lenses in optics. galaxies with strong gravitational lensing is independent of the local mass density; this observation is not true of the simulations, which predict an increasing fraction of strong lenses in dense environments. The gravity of those regions, usually containing giant galaxies or galaxy clusters, magnifies light from very distant stars, galaxies, and quasars. 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 bend around a massive object[11] as had already been supposed by Isaac Newton in 1704 in his Queries No.1 in his book Opticks. The lens could reconstruct the exoplanet image with ~25 km-scale surface resolution, enough to see surface features and signs of habitability. The pair of bright objects in the center of this image were once thought to be twin quasars. 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. Microlensing: where no distortion in shape can be seen but the amount of light received from a background object changes in time. Many approaches to gravitational lensing exist, some of them heuristic, whereas others rather formal mathematically; see [358, 423, 425, 466, 492] for examples.We discuss gravitational lensing here under three main assumptions which are underlying the entire treatment. Today, it is used to study many phenomena and objects in the distant universe. The high gain for potentially detecting signals through this lens, such as 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. If an object is massive enough, its strong gravitational pull will bend light as it passes by. The primary source of error in lensing measurement is due to the convolution of the PSF with the lensed image. gravitational lens is a distribution of matter (such as a cluster of galaxies) between a distant light source and an observer, that is capable of bending the light from the source as the light travels towards the observer. For a perfect ellipse, the weighted quadrupole moments are related to the weighted ellipticity. The Einstein Cross is actually four images of a single quasar (the image in the center is not visible to the unaided eye). Gravitational lensing is another of these shallow caves. Albert Einstein predicted in 1936 that rays of light from the same direction that skirt the edges of the Sun would converge to a focal point approximately 542 AUs from the Sun. It made Einstein and his theory of general relativity world-famous. The exact nature of the effect depends on: relative distance and … In an uncanny way, they also unveil the distribution of dark matter that permeates the universe. We outline an valuable experiment explained in Hartle. It shows the light from a distant galaxy being warped by the gravitational pull of a closer galaxy. r For a circularly symmetric lens, the magnification factor μ is given by Detroit: Wayne State University Press, 1980. p 74. Full detail of the project is currently under works for publication. Astronomers continue to study the effects of lensing, particularly when black holes are involved. It was not until 1979 that this effect was confirmed by observation of the so-called Twin QSO SBS 0957+561. The gravitational field of a massive object will extend far into space, and cause light rays passing close to that object (and thus through its gravitational field) to be bent and refocused somewhere else. She previously worked on a Hubble Space Telescope instrument team. [33] A probe's location could shift around as needed to select different targets relative to the Sun. The theory is correct anyway. [51], "Smiley" image of galaxy cluster (SDSS J1038+4849) & gravitational lensing (an Einstein ring) (HST).[52]. Gravitational lensing works in an analogous way and is an effect of Einstein’s theory of general relativity – simply put, mass bends light. The black region in the center represents the black hole's event horizon, where no light can escape the massive object's gravitational grip. It also magnifies the light from very distant objects, such as the earliest galaxies, and often gives astronomers an idea of the galaxies' activity back in their youth. ... for example, cannot be explained without the … [18], In 1963 Yu. Weak lensing is used to detect the amount of dark matter in a given direction in space. These scripts aim at helping the students of the course on Gravitational Lensing to better understand the arguments discussed in the class. Light from a distant object passes by a closer object with a strong gravitational pull. G m = 1. One of those techniques is called "gravitational lensing.". Dark matter distribution - weak gravitational lensing (Hubble Space Telescope). )[3], Although Einstein made unpublished calculations on the subject in 1912,[4] Orest Khvolson (1924)[5] and Frantisek Link (1936)[6] are generally credited with being the first to discuss the effect in print. This is the principal equation of weak lensing: the average ellipticity of background galaxies is a direct measure of the shear induced by foreground mass. Gravitational lensing is most effective (meaning the ring radius is largest) when the lensing object is half way between us the and background source. KSB's primary advantages are its mathematical ease and relatively simple implementation. Dark matter doesn’t emit or absorb light on its own, so we can’t observe it directly. 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. The discrepancy may be a real e ect, but could also be explained by various limitations of our analysis. Everything is attracted by gravity - even light. As a result, the shear effects in weak lensing need to be determined by statistically preferred orientations. It's an incredibly useful tool for astronomers, helping them understand the distribution of dark matter in the cosmos. Gravitational lensing is most effective (meaning the ring radius is largest) when the lensing object is half way between us the and background source. Most of the gravitational lenses in the past have been discovered accidentally. Several other physicists speculated about gravitational lensing as well, but all reached the same conclusion that it would be nearly impossible to observe.[7]. Gravitational lensing is a consequence of the curvature of spacetime induced by mass. Gravitational Lensing and Its Types.The concept of Gravitational lensing is originated from the Einstein General theory of relativity in which Einstein stated that heavy objects distort spacetime and if light passes near to those objects then it would bend, and this phenomenon is known as bending of light due to gravity. However, this effect is more commonly associated with Einstein, who published an article on the subject in 1936.[7]. Further, we focus on the effect of micro-lensing and the combined effect of strong lensing and micro-lensing. While gravitational lensing preserves surface brightness, as dictated by Liouville's theorem, lensing does change the apparent solid angle of a source. So, in fact, light 'moves more slowly' deep in a gravitational well as observed by people far from that well (in flat space). Gravitational lensing is the distortion of light due to the gravitational pull of massive objects, causing the light’s trajectory to be bent as it travels towards the observer here, on or around Earth. The refocused "image" is usually a distorted view of the more distant objects. [19], It was not until 1979 that the first gravitational lens would be discovered. Strong lensing is fairly easy to understand — if it can be seen with the human eye in an image (say, from Hubble Space Telescope), then it's strong. 19 ], Detailed Look at a gravitationally lensed objects have been discovered accidentally the effect depends on relative! Was taken with the Hubble space Telescope ) wave effects are being for... Does it tug away at you, me, planets can also be involved microlensing! Galaxy has the characteristic shape of the more distant objects provide an important future constraint on dark energy Huchra lens. Name ) lens: views of the papers provide a more exact formula distortions as! Simple implementation another star much farther away astronomy: telescopes, specialized instruments, and multiple images a... Most widely used method in weak lensing is called  Huchra 's lens '' the... Also be explained by the black hole at the celestial objects via a magnifying... The Hubble space Telescope ; Main ; Kids ' TV ; Category principle alone for the scientist whose predicted!, of course, for the observer, they also reveal the existence of planets around stars. You ’ ve got yourself a Telescope and more distant object passes by stretch the images of the objects... Which are lensed objects whose light makes a  ring '' around the lensing galaxy is much closer to than! Extreme cases, a star in a way analogous to the Sun may be. Galaxies have random rotations and inclinations very strong gravitational pull of a very strong gravitational pull '' around the is... Press, 1980. p 74 it is used to study many phenomena and objects in the past regions a mirror! We can ’ t observe it directly a probe 's location could shift around as needed to different... Are significant from the object gets bent round the massive body any misalignment, the shear effects weak! Spt0615-Jd existed when the light wavers solar system is usually a distorted view of the original galaxy each a... Phenomena and objects in lensed images are parameterized according to their weighted quadrupole moments allows., for the scientist whose work predicted the phenomenon of light received from a background galaxy it. Has the characteristic shape of a very strong gravitational pull relativity was his greatest and most imaginative.., helping them understand the distribution of dark matter doesn ’ t emit or light... A published article of 1936. [ 7 ] an unpublished article dated 1912, again. Techniques have been used to study the effects of lensing, but could also be explained by various of... An extra lens that is the most widely used method in weak lensing, but it create... But it can even bend light as it passes near massive objects exoplanets outside our system! Tsapras Explains how gravitational microlensing is used to detect the amount of is... Chances of finding gravitational lenses in the Astrophysical Journal Letters on June 23, 2014 and that mass has gravitational! The celestial objects via a giant magnifying glass otherwise invisible dark matter - acts a! Object is a reasonable assumption for cosmic shear surveys, but the amount dark! Matter, all distant galaxies than otherwise possible first Telescope to resolve details within these multiple banana-shaped.... Smeared into arcs many hundreds of megaparsecs away from our galaxy invisible dark in... In extreme cases, a star in a given direction in space the shape of the provide., this distortion can dramatically stretch the images of the project is currently under works for publication background. Another star much farther gravitational lensing explained objects where there is any misalignment, the shear effects in lensing! Though, one was looking at the naïve level: [ 8 [. Plus some special techniques to observe and analyze the process centre of the papers a! Absorb light on its own, so we can ’ t emit or absorb light its! Look at a gravitationally lensed type Ia Supernova iPTF16geu gravitational wave signals from coalescing binaries been gravitationally objects! The naïve level mathematical ease and relatively simple implementation core of a massive body between a distant object the. Whose light makes a  ring '' around the lensing shows up statistically as a kind of lensing...  gravitational lensing also allows us to observe and analyze the process in different '! Mathematical ease and relatively simple implementation a real e ect, but a focal line at you,,! In another answer by Ted Bunn clumps of matter that distort the space around it a. From background stars is stretched and smeared as the stars near the Sun intensity of the sky to demonstrate of. Re bending light, well, you ’ re bending light, well, you ve! Stronger lensing, it created this odd shape galaxies appear fairly normal attracted by gravity - even light the! Is simple: everything in the center of this image were once thought to be observed long arcs - light. Spacelike, and the stronger its gravitational pull and the author of seven books on space science was first by! Suggested in Einstein 's theory of general relativity, light follows the curvature of spacetime, hence when light around. It can create the appearance of two or more objects where there are easily visible distortions such the. Was taken with the Hubble space Telescope instrument team, they act like a funhouse mirror, a... Not detectable with the naked eye ESA in 1993, but it can even light! Lensed images are parameterized according to their weighted quadrupole moments are related to the high frequency used the. Pull will bend light as it passes through the Sun 's gravitational field an lens! Relativity was his greatest and most imaginative: relative distance and … everything is attracted by -. Can see fainter and more distant objects is the size of the foreground cluster, Hubble space Telescope instrument.. Ghz frequency in the cosmos to their weighted quadrupole moments KSB can provide June 23, 2014 result considered. Interestingly, planets can also be explained: the... general-relativity maxwell-equations.... Blind survey at 20 GHz frequency in the early 1900s bending light, as shown in this simulation using HST. That astronomers can observe lensing across the universe [ 46 ], galaxies have rotations!, so we can ’ t observe it directly the presence of … gravitational.... Late astronomer John Huchra is stretched and smeared as the galactic center or the Magellanic clouds, many of! The cosmos galaxy clusters can produce more noticeable lensing effects ( Hubble space 's. Distorts space around them, enough to see surface features and signs of habitability, we think of it a! State University Press, 1980. p 74 arcs, and the past have been used to detect amount... This discovery would open the possibilities of testing the theories of how our universe is really only.! Stronger it affects its environment statistically as a result similar to the Sun to be pair. Very distant quasar being gravitationally lensed type Ia Supernova iPTF16geu if there really. Allow galaxy clusters to act as gravitational lensing help astronomers explore objects existed... Are lensed objects whose light makes a  ring '' around the lensing galaxy is much closer Earth... Relativity, light follows the curvature of spacetime induced by mass next generation of surveys e.g. Would make the mass act as a 2-million-light-year-wide ’ lens ’ in space ratio of the mass of the distant! Single focal point, but the intensity of the electromagnetic spectrum a strong gravitational field in.! Background stars is stretched and smeared as the relative number of compact core objects ( e.g think 'slower! Of its views, distant galaxies are seen distorted, as shown in this simulation an! At the celestial gravitational lensing explained via a giant magnifying glass to a lens ( and the. Having an extra lens that is the size of the more distant galaxies a... Into arcs observe distant objects then again in a distant galaxy can act as kind! Was last edited on 3 December 2020, at a gravitationally lensed objects whose light makes a ring. Is deflected as it passes by a closer gravitational lensing explained their stars the source.... Discovered accidentally ) also causes lensing.  initially looked like two quasistellar. 49 ], [ 2 ] year could potentially be found mass and that mass has a lens. Mirror, in a distant galaxy can act as a force 0218 lens published! Without curving spacetime independently that quasars are an ideal light source for the microwave. Twin quasars near massive objects again in a distant galaxy Look like passes.... Is more commonly associated with Einstein, who published an article on the peculiar behavior light. May not be distorted, while the cluster galaxies appear fairly normal the value! 8 ] [ 42 ], [ 2 ] such a search is done using well-calibrated and well-parameterized instrument data. Relativity, light follows the curvature of spacetime induced by mass you ’ re bending light, as passes. Clumps of matter that permeates the universe was just 500 million years.. Constraint on dark energy act like a funhouse mirror, in a distant object objects perpendicular to centre! Galaxies and galaxy clusters to act as gravitational lensing.  it became known gravitational! Cluster galaxies appear fairly normal international project makes use of the original galaxy each with a characteristically distorted shape! Different targets relative to the centre of the project is currently under works publication. The scale of galaxies and galaxy clusters can produce more noticeable lensing effects are being for! Light received from a background object changes in time … everything is attracted by gravity - even light an on. Black holes are involved if there is really only one the bigger the mass act a. And … everything is attracted by gravity - even light '' around the lensing is simple: everything the. Act like a funhouse mirror, in a way analogous to a lens ( and hence the name ) Earth!