What is Gravitational lensing: Definition and 82 Discussions

A 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. 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. (Classical physics also predicts the bending of light, but only half of that predicted by general relativity.)Although Einstein made unpublished calculations on the subject in 1912, Orest Khvolson (1924) and Frantisek Link (1936) are generally credited with being the first to discuss the effect in print. However, this effect is more commonly associated with Einstein, who published an article on the subject in 1936.Fritz Zwicky posited in 1937 that the effect could allow galaxy clusters to act as gravitational lenses. It was not until 1979 that this effect was confirmed by observation of the so-called Twin QSO SBS 0957+561.

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  1. R

    Astrophysics Problem (gravitational lensing)

    Homework Statement I need some help with the following problem: http://img543.imageshack.us/img543/9630/lensq.jpg The Attempt at a Solution First I have tried to work out the radius of the Einstein ring: r_E = \sqrt{\frac{4GM}{c^2}}.\sqrt{\frac{D_1D_{1s}}{D_s}} =...
  2. S

    Gravitational lensing due to earth

    It is known that light from stars bend near surface of sun due to its mass. Similarly light will bend near Earth's surface (may be insignificant due to less mass). My question is that sunlight that strikes Earth's surface travels a straight path from sun or a curves near Earth's surface ?
  3. grav-universe

    Gravitational lensing derivation using equivalence principle

    I have been trying to work this out for the last couple of weeks, but I just keep getting the Newtonian deviation in angle for a path of a photon traveling from x=-∞ to x=∞. At first I tried putting the actual path into a computer simulation, transforming back and forth between the hovering...
  4. Angelos K

    Multiple images in gravitational lensing

    Dear all, so far I have only studied weak lensing. Therefore I understand little about multiple images.The light paths, by Fermat's principle, have to correspond to stationary points of the (proper) time delay. Minima, maxima saddle points. Basics are nicely reviewed here [p.14]...
  5. H

    3D cloaking changing gravitational lensing ?

    Do the new optical and time shifting versions of 3D cloaking present a challenge to gravitational lensing as a valid proof of gravity ? Am curious if the time shifting constituent of the theories can mimic the redshifting observed in arcs and lenses also. Seems that with the findings of...
  6. H

    Gravitational lensing and the speed of light

    Hello all, Would like to get some feed-back on some questions I had about special/general relativity and a thought experiment. In the case of gravitational lensing, an obvious case being the Earth is lined up with the sun which is lined up with a distant star. From Earth the star is seen...
  7. L

    Gravitational lensing anomaly?

    Hi, The recent Astronomy Picture of the Day: http://apod.nasa.gov/apod/ap111221.html Has the following caption: ...the gravity of a luminous red galaxy (LRG) has gravitationally distorted the light from a much more distant blue galaxy. I was under the impression that the more...
  8. 6

    Gravitational Lensing or Inferior Mirage?

    Can gravitational lensing also be explained by the refraction of light from a more distant object through a gradient of radiant heat and dense cool space? Same difference? Or completely separate and unrelated? If unrelated, how can this optical phenomenon be determined as a result of...
  9. G

    Gravitational Lensing deflection angle question

    I wasn't sure whether this was the right place to post this since it isn't really coursework, but it seems like it could be. My problem is with the deflection angle of light for several point masses. The deflection for a point mass can be described as: \frac{4GM}{c^{2}\xi} where \xi...
  10. J

    Einstein's 1911 prediction (Gravitational Lensing)

    Hi. I am trying to make my way through http://www.mathpages.com/rr/s8-09/8-09.htm one step at a time if I have too. I already got stuck once, where it says: The paper makes it sound like these two variables are constant, but the way it should be defined is "Let t1 be the time...
  11. T

    Photon wavelength shift from gravitational lensing?

    The basic question is: will a photon traveling through a vacuum lose some of its energy due to interactions with gravity from a massive body? Gravitational lensing implies that the photon will change its initial direction but is its energy conserved (i.e. differences in blueshift/redshift...
  12. M

    Gravitational lensing paradoxon

    Let us assume that two light rays are started at the same time symmetrically (towards the left and towards the right side of the star) which are diffracted due to the gravitational effect of a star and they meet each other at the same place behind the star. The meeting is the same event...
  13. A

    Fermats P & Gravitational Lensing

    Fermat's principle states that light travels the path of stationary time, I've read up on this from several sources and I've come to realize that this means that it will travel paths of extrema, (maxima, minima & saddle points). For minima, refraction is often given as an example (minizing...
  14. J

    Gravitational lensing and red shift

    Hi I'm new to the forums. I have a question I hope you guys can help me understand. When gravitational lensing produces multiple images of the same object, do they undergo any red/blue shift? And if so, is the frequency shift the same for each image?
  15. J

    Can Chromatic Aberration arise from Gravitational Lensing?

    I've been puzzled by this. If light of different frequencies (like ultra violet to infra-red) would experience different refraction angles in the presence of a powerful gravity field. I understand that light has zero rest mass but has effective mass given the fact it's in motion. What I'm...
  16. scupydog

    Gravitational lensing angle equation

    Hello. In the attached a diagram there are 2 stars on the left, the upper star is the apparent position as veiwed from Earth and the lower star the true position. The central star is the Sun Could anyone give or direct me to an equation for the angle by which the light is deflected aº in...
  17. N

    Can Gravitational Lensing Cause a Star to Appear Twice Simultaneously?

    Gravitational lensing displaces the apparent direction of a star outwards away from a gravitational source. Do you think it would be possible to see the same star at least twice simultaneously, one either side of this gravitational source? Even more likely, if the gravitational source was great...
  18. D

    Gravitational lensing - 2 questions

    Observer O sees object S in the imaginary position S', because of the gravitational lensing caused by the heavy mass M. Question 1. If O is positively charged and S is negatively charged, in what difrection acts the coloumb force - S or S' ? Question 2. If S is massive (but is still much...
  19. L

    Gravitational Lensing: Extent & Effects on Universe

    What is the extent of gravitational lensing? i mean, if every single star, black hole, galaxy ect is lensing light in all directions it would surely make the true nature/structure of the universe far different than is observable, right? we could be seeing the same object in two completely...
  20. J

    Gravitational Lensing Deflection angle

    Does anyone know where I could find (online) a derivation of the deflection angle in gravitational lensing: alpha = 4GM/Rc^2 Thank you
  21. M

    Gravitational lensing and diffraction patterns

    Does gravitational lensing cause diffraction patterns, such as those seen by single, double, etc slit diffraction? In other words, would x-rays from object X get bent "less" than say microwaves or infrared? Would this happen if the light was passing between binary stars only, or could it...
  22. N

    Question on gravitational lensing

    I was wondering whether one has examined the spectrum of gravitational lensed light (nice description on wikipedia : http://en.wikipedia.org/wiki/Gravitational_lensing ). Have there been indications on some red or blue shifts in the light from different parts of the observed ring? Does anyone...
  23. J

    Gravitational lensing and Dark matter

    Does anyone know if gravitational lensing confirms the existence of Dark matter?
  24. wolram

    Gravitational Lensing and Frequency-Dependent Light Travel Time

    Light that has traveled millions of years is gravitationaly (lensed) around a body, if there is any frequency dependant light travel time ,would it not show up as if it had been split by a prism when it was lensed around said body, or would the various frequencies recombine?
  25. S

    Can Fermat's principle be applied to gravitational lensing?

    Light having to travel through a gravitational field deflects towards the mass and thus increases the length and duration of its journey (traveling through more curved space-time takes more proper time than traveling through less curved space-time) I understand that unlike in refraction, light's...
  26. S

    Gravitational Lensing: Learn More about Einstein Rings

    I read that when a galaxy comes in the path of light coming from a quasar, its path bends slightly resulting in the formation of a giant luminous arc (called einstein ring). The phenomenon is called gravitational lensing. Can someone tell me something more about gravitational lensing ? Please...
  27. H

    Gravitational Lensing: Where to See It Through a Telescope

    Hi I was wondering where in the universe is gravitational lensing that i can see first hand through my telescope. Thanks!:biggrin:
  28. C

    Gravitational Lensing & Light?

    Why does light bend when it encounters a black hole or a star? Does a black hole have a refractive index? It must depend on its mass if it does. A star can produce an effect knows as gravitational lensing which bends light in much the same way as an optical lens bends light, how does this...
  29. B

    Gravitational Lensing: Why Does it Only Create Clones?

    I was wondering... Why doesn't Gravitational Lensing ever create a ring when bending light from an obstructed star? It seems to always create 2,3 or 4 clones of the star. I can't get my head around this, maybe I'm missing something fundamental? Your posts are appriciated. Regards, Sam
  30. R

    Gravitational Lensing: How Does it Work?

    I have heard of two physical phenomena: 1. A photon traveling from one location to another, goes the path that takes the shortest time. (More correctly, the quickest paths has the highest probability amplitude) 2. Time is slowed down in a gravitational field. Is this how gravitational...
  31. S

    Shapiro Effect and Gravitational Lensing

    I have been searching for alternatives to BBT and the doppler effect to explain everything, and have been dissapointed to find a lot of crackpots out there. I have recently found this website: http://www.geocities.com/newastronomy/Index.htm and the thing makes all kinds of sense (to my...
  32. G

    Why Does Einstein's Theory Predict an Odd Number of Gravitational Lens Images?

    Gravitational Lensing - question An article published today at http://spaceflightnow.com/news/n0402/11lens/ stated that "Einstein's general theory of relativity predicts there should be an odd number of images, yet almost all observed lenses have only 2 or 4 known images." How and Why does...
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