Gravitational lensing and red shift

In summary, gravitational lensing does not cause any red/blue shift of light deflected by a massive body. This is because the effect is very small and usually cancels out due to equal amounts of blueshift and redshift. However, if the gravitational potential changes during the time light is traversing the object, there may be a noticeable change in redshift. This can occur when light is lensed by a very large object, such as a galaxy. The anisotropies in the CMB are also affected by this effect. Additionally, if you are close to a black hole, light from distant stars may be blue shifted, while light from sources closer to the black hole will be red shifted.
  • #1
jollett
3
0
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?
 
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  • #2
jollett said:
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?

No, there is no red/blue shift of light deflected by a massive body. At least, nothing of that sort has been observed. In principle, one can expect that photons passing near a massive body should lose a part of their energy (and frequency) due to the tidal effect. However, this effect is very small.

Eugene.
 
  • #3
meopemuk said:
No, there is no red/blue shift of light deflected by a massive body. At least, nothing of that sort has been observed. In principle, one can expect that photons passing near a massive body should lose a part of their energy (and frequency) due to the tidal effect. However, this effect is very small.

Eugene.

Are you saying that gravitational fields don't shift light? Do you mean that there is no difference between the redshift of two equidistant galaxies, one of them being lensed by a closer gravitational object? Is this always true or is this because the shift is so small it's undetectable, and if redshift is subject to the curvature of space, could there be a noticeble change in redshift if the lensing object is massive enough or the distance of the lensed object is even further away?

Don't gravitiational fields affect time? Surely an intervening gravitational lensing body would have some kind of time effect on the light being lensed around it as well as the distance the light has to travel being increased due to the curvature of space around the lensing object?
 
  • #4
Usually, for gravitational lensing, the blueshift incurred while the light is "dropping into" the gravitational potential matches the redshift incurred while the light is escaping from the gravitational potential, so that the net effect is 0. This is not true if the gravitational potential changes during the time light is traversing the object. I think this happens when light is lensed by a very large object (e.g. a galaxy) rather than like a star, but I'm not sure. I do know that the anisotropies in the CMB are due to this effect (there's a paper on it, but I forget by who).
 
  • #5
Matterwave said:
Usually, for gravitational lensing, the blueshift incurred while the light is "dropping into" the gravitational potential matches the redshift incurred while the light is escaping from the gravitational potential, so that the net effect is 0. This is not true if the gravitational potential changes during the time light is traversing the object. I think this happens when light is lensed by a very large object (e.g. a galaxy) rather than like a star, but I'm not sure. I do know that the anisotropies in the CMB are due to this effect (there's a paper on it, but I forget by who).


Right. If you were close to a black hole then light from distant stars would be blue shifted. If the light source is closer to the black hole than you are then the light you see will be red shifted.
 

1. What is gravitational lensing and how does it occur?

Gravitational lensing is a phenomenon that occurs when the path of light from a distant source is bent as it passes near a massive object, such as a galaxy or cluster of galaxies. This bending of light is caused by the gravity of the massive object, and it can create distorted or magnified images of the source. This effect was first predicted by Einstein's theory of General Relativity.

2. How does gravitational lensing affect our understanding of the universe?

Gravitational lensing allows us to see objects that would otherwise be too faint or too far away to observe. It also provides a way to study the distribution of dark matter in the universe, as the lensing effect is influenced by the amount of mass in the lensing object. By studying gravitational lensing, we can gain insights into the structure and evolution of the universe.

3. What causes red shift in light and how is it related to gravitational lensing?

Red shift is a phenomenon that occurs when the wavelength of light is stretched, causing it to appear more red. This stretching of light can be caused by the Doppler effect, which is the result of an object moving away from us. In the case of gravitational lensing, the bending of light by massive objects can also cause a red shift in the light from distant sources, as the light must travel a longer path to reach us.

4. Can gravitational lensing be used to study other objects besides galaxies?

Yes, gravitational lensing can also be used to study other massive objects in the universe, such as black holes and quasars. In fact, gravitational lensing has been used to discover and study some of the most distant and massive black holes known.

5. How is gravitational lensing different from other types of lensing, such as optical lensing?

Gravitational lensing is different from other types of lensing, such as optical lensing, because it is caused by the distortion of space-time by massive objects, rather than by the physical properties of a lens. This means that gravitational lensing can occur on a much larger scale and can be used to study objects that are much farther away than what is possible with traditional optical lenses.

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