Einstein cross and gravitational lensing

[pavelcherepan]

Hi everyone!

 

This may be a silly question but anyway here goes. So with Einstein cross we have a quadrupled image of a distant quasar which happens due to gravitational lensing by a nucleus of a spiral galaxy in the foreground. Why do we see 4 distinct images of the quasar? I mean, if a quasar is sort of directly behind the lensing galaxy and if the gravitational field of galactic nucleus is more or less uniform I would expect to see a blurred circle, not 4 separate images. What am I missing here?

Edited April 1, 2015 by pavelcherepan

[Spyman]

I think you got it already, they are not lined up perfectly and the gravity field is not uniform.

 

Hundreds of gravitational lenses are currently known. About half a dozen of them are partial Einstein rings with diameters up to an arcsecond, although as either the mass distribution of the lenses is not perfectly axially symmetrical, or the source, lens, and observer are not perfectly aligned, we have yet to see a perfect Einstein ring.

http://en.wikipedia.org/wiki/Einstein_ring

[pavelcherepan]

Oh, cool, thanks! For some reason I missed the part about rings