Question on gravitational lensing

[notknowing]

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 know?

Rudi Van Nieuwenhove

 

[notknowing]

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 know?

Rudi Van Nieuwenhove

I realized that I should have been more specific. What I meant is "has one observed variations in red shifts in the light from different parts of the ring ?"

 

[Chris Hillman]

Are you talking about an Einstein ring? (There are a few examples of almost perfect Einstein rings which have been observed.) What kind of variations do you have in mind?

 

[meopemuk]

As far as I know, the gravitational deflection of light should not affect light's frequency. If there are experiments showing the opposite I would be interested to get the reference.

Eugene.

 

[Chris Hillman]

Well, in gtr, light bending certainly does not depend on frequency (in the geometrical optics approximation), but it's not clear to me what he has in mind.

 

[notknowing]

Well, in gtr, light bending certainly does not depend on frequency (in the geometrical optics approximation), but it's not clear to me what he has in mind.

Sorry for the late reply (have been sick). I was just wondering whether some strong kind of space-dragging effects around rotating galaxies or rotating black holes could possibly lead to a shift in frequency. Or would it only lead to a time difference ?

 

[Chris Hillman]

Straightening out Light-bending (Mk1:3)

Rudi, sorry, but I don't yet understand your question. Did you take the point (already mentioned by meopemuk) that according to gtr, "light bending" (e.g. in "gravitational lensing") does not depend on the frequency of the light being bent?

 

[notknowing]

Rudi, sorry, but I don't yet understand your question. Did you take the point (already mentioned by meopemuk) that according to gtr, "light bending" (e.g. in "gravitational lensing") does not depend on the frequency of the light being bent?

Yes, I know that light bending as such does not depend on the frequency of the light. The question is what happens in case of strong frame dragging effects, so in which the galaxy or black hole has a very large mass and high angular momentum. What would happen if we observe lensed light (from stars far beyond this large rotating mass) in this case? At one side, the light would encounter a "space rotation" in the same direction as the propagating light and at the other side the "space rotation" would be in the other direction. How would this show up in the observed light. I know the effects are small, but I'm just wondering about the physical effect.

Rudi Van Nieuwenhove

 

[Chris Hillman]

This is discussed extensively in Chandrasekhar, Mathematical Theory of Black Holes.