Does Gravitational Lensing Cause Red Shift in Light?

In summary, light does get redshifted during lensing when passing by a massive object such as a galaxy or cluster. However, the effects on measurements of the Cosmic Microwave Background Radiation (CMBR) and distant redshifted galaxies are negligible. The added length of the path does not significantly contribute to redshifting. Refraction and lensing do not change the frequency of light. The Sachs-Wolfe effect is a special case that occurs when photons pass through a massive extended body, causing them to be slightly less redshifted when exiting the region. This effect is only significant for extremely large systems, where the dominant cause of changing gravitational potential wells is dark energy.
  • #1
Tanelorn
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Does light get red shifted during lensing, when it passes by an object with great mass such as a galaxy or cluster?

If so then what are the effects on measurements of the CMBR and most distant red shifted galaxies?

If true then presumably some light would be red shifted more than others resulting in frequency dispersion?
 
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  • #2
Think about shining a laser horizontally along a road from point A to point B, one mile apart and each one foot off the ground. Now put a 2 foot diameter beach ball in the middle of the path and require that the light beam go from point A to a point just above the beach ball and then on to point B. I don't think the added length of the path would cause any significant red shifting.

I think the CMB measurements ignore any lensing, and since lensing really is only used to show the effects of GR, it's irrelevant to measurements of distant galaxies (assuming I'm right about the added red shift being insignificant).

All of this is just what I hope is an educated guess. I haven't done any math on this and if I'm off, I'm sure someone more knowledgeable will jump in and let us know.
 
  • #3
What if the light bends around an object and significantly changes direction?
 
  • #4
Tanelorn said:
What if the light bends around an object and significantly changes direction?
That might make very slightly more difference, but that is not what happens with galactic lensing.
 
  • #5
Tanelorn said:
What if the light bends around an object and significantly changes direction?
Doesn't really matter. Lensing just changes the direction of light beams. It doesn't impact their wavelength. It does change light travel time and distance, which may have some impact on the redshift, but it's a very minor impact. I doubt it is measurable.
 
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Light gets blueshifted as it approaches a massive body then redshifted by the same amount as it departs. The net effect is zero - re: http://curious.astro.cornell.edu/ab...hen-it-is-gravitationally-lensed-intermediate. There is, however, a special case called the Sachs-Wolfe effect that occurs when photons pass through a massive extended body. Those photons are slightly less redshifted when they exit such a region.
 
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  • #8
Chronos said:
Light gets blueshifted as it approaches a massive body then redshifted by the same amount as it departs. The net effect is zero - re: http://curious.astro.cornell.edu/ab...hen-it-is-gravitationally-lensed-intermediate. There is, however, a special case called the Sachs-Wolfe effect that occurs when photons pass through a massive extended body. Those photons are slightly less redshifted when they exit such a region.
Just to expand upon the Sachs-Wolfe effect, this occurs as a result of the gravitational potential well changing over the time the photon passes through it. Obviously this will only be a significant effect for extremely large systems, where the dominant cause of changing gravitational potential wells is dark energy, which causes the gravitational potential of large systems to decay slowly over time.
 
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What is red shift due to lensing?

Red shift due to lensing is a phenomenon in which light from a distant object is bent or distorted by the gravitational pull of a massive object, such as a galaxy or a black hole. This bending of light causes the wavelength of the light to appear longer, resulting in a shift towards the red end of the spectrum.

How does red shift due to lensing occur?

Red shift due to lensing occurs when light passes through a region of space with a strong gravitational field. The gravitational pull of the massive object causes the path of the light to curve, resulting in a change in its wavelength and thus a red shift.

What is the significance of red shift due to lensing?

Red shift due to lensing is significant because it provides a way for scientists to study and measure the mass and distribution of dark matter in the universe. It also allows for the detection and study of distant galaxies and objects that would otherwise be too faint to observe.

How is red shift due to lensing measured?

Red shift due to lensing is measured using spectroscopy, which involves analyzing the spectrum of light emitted by an object. By comparing the observed spectrum to the expected spectrum, scientists can determine the amount of red shift and calculate the amount of gravitational lensing that has occurred.

Are there different types of red shift due to lensing?

Yes, there are two types of red shift due to lensing: gravitational lensing and cosmological red shift. Gravitational lensing occurs due to the bending of light by a massive object, while cosmological red shift is caused by the expansion of the universe. Both types of red shift can be observed and studied by scientists to learn more about the structure and evolution of the universe.

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