# Gravitational Lensing and Redshift

• SHISHKABOB
In summary, it appears that there is not a significant change in the redshift of an image that is lensed.

#### SHISHKABOB

hi there, I was just at a seminar in which the speaker was talking about using gravitational lensing to investigate galaxy clusters

my question is pretty simple: is there any effect on the redshift of the image of an object which is "lensed" by the gravitational lensing phenomenon? I would imagine that it would not, because all that's going on is bending of the path that the light is taking. However, I am not very well educated on the topic, and perhaps there are things that I am not taking into account.

A photon is blue shifted as it enters a gravitational field, then redshifted by the same amount as it exits. Intervening matter [i.e., a lensing body] has no effect.

Chronos said:
A photon is blue shifted as it enters a gravitational field, then redshifted by the same amount as it exits. Intervening matter [i.e., a lensing body] has no effect.

Is this because the force of the gravity on the photon as it enters the gravitational field 'pulls' the photon inward, thus shortening the wavelength and blueshifting it? And as it leaves the gravitational field, the gravity is pulling on it, which causes the wavelength to increase, thus redshifting it?

Light Bearer said:
Is this because the force of the gravity on the photon as it enters the gravitational field 'pulls' the photon inward, thus shortening the wavelength and blueshifting it? And as it leaves the gravitational field, the gravity is pulling on it, which causes the wavelength to increase, thus redshifting it?

Pretty much, yes.

Chronos said:
A photon is blue shifted as it enters a gravitational field, then redshifted by the same amount as it exits. Intervening matter [i.e., a lensing body] has no effect.

thanks

Is there enough space in local group that lensed image through one can have measurable difference of cosmological redshift compared to its sister image through "clean" space?

## 1. What is gravitational lensing?

Gravitational lensing is a phenomenon in which the gravitational pull of a massive object, such as a galaxy or cluster of galaxies, bends and magnifies the light from objects behind it, making them appear distorted or duplicated.

## 2. How does gravitational lensing affect our observations of distant objects?

Gravitational lensing can magnify and distort the light from distant objects, allowing us to see them in more detail and from different angles. It can also create multiple images of the same object, giving us a better understanding of its shape and structure.

## 3. What is the difference between strong and weak gravitational lensing?

Strong gravitational lensing occurs when the lensing object is massive enough to create distinct and highly distorted images of the background object. Weak gravitational lensing, on the other hand, produces subtle distortions in the shape of the background object.

## 4. How does redshift play a role in gravitational lensing?

Redshift is a phenomenon in which light from distant objects appears shifted towards longer wavelengths due to the expansion of the universe. In gravitational lensing, the redshift of the background object can be used to measure the mass and distribution of the lensing object.

## 5. Can gravitational lensing be used to study dark matter?

Yes, gravitational lensing can be a powerful tool for studying dark matter, as it can reveal the presence and distribution of this invisible substance through its gravitational effects on light. By studying the lensing of light from distant objects, scientists can map out the distribution of dark matter in the universe.