by JohnD » Sun Dec 17, 2017 3:31 pm
Thank you, Chris, but ...'oblong' ? A rectangular solid, with faces that have equal opposite sides? I suppose that might focus four images!
Would a classic spiral galaxy have an 'oblongish' gravity field? Equal on either side of the poles, and either side of the disc, but different in either position?
But, this page by Louis Marmet addresses my question, and says, " If the mass is concentrated in a small volume, only two images are produced by the gravitational lens (and if the quasar is centered on the lensing mass, a ring appears)"
http://www.marmet.org/cosmology/einsteincross/ Marmet explains the second pair by supposing that the lensing mass is not a point source, "but the lens would need to have a very complex shape."
I've learnt today!
John
Thank you, Chris, but ...'oblong' ? A rectangular solid, with faces that have equal opposite sides? I suppose that might focus four images!
Would a classic spiral galaxy have an 'oblongish' gravity field? Equal on either side of the poles, and either side of the disc, but different in either position?
But, this page by Louis Marmet addresses my question, and says, " If the mass is concentrated in a small volume, only two images are produced by the gravitational lens (and if the quasar is centered on the lensing mass, a ring appears)" http://www.marmet.org/cosmology/einsteincross/ Marmet explains the second pair by supposing that the lensing mass is not a point source, "but the lens would need to have a very complex shape."
I've learnt today!
John