Re: gravitational lensing

[John Roberts <roberts@xxxxxxxxxxxxxxxxx>]

>Date: Thu, 7 Mar 1996 20:28:00 -0600
>From: telscope@xxxxxxxxxx (Peter Abrahams)
>Subject: gravitational lensing

>A recent post referred to gravitational lensing of light from distant
>galaxies, and asked whether multiple images of the galaxy would be stereo
>pairs.  Such questions boggle the mind and leave me speechless at the reach
>of the unfettered imagination.
>...I do not believe they would be a stereo pair.  
>--The images are extremely faint, fuzzy and small.
>--They are smeared, and are not a likeness.  The smearing is symmetrical,
>and the images make right and left hand pairs.
>--The more distant galaxy is an enormous distance behind the nearer galaxy.
>The stereo base is the width of the near galaxy, probably small compared to
>the intergalactic distance.

I'm not sure about the last item, but agree that the others would be a
problem. One source I read noted that if the gravitational lens were completely
symmetric, the resulting image would be a ring. Asymmetries in the lens can 
result in two or four ("Einstein cross") images that look more or less like the
original light source. But I don't think this ever occurs without some sort of
distortion. It's conceivable that computer analysis could pick out some
corresponding distinctive features and reconstruct a partial 3D model.

John R. [See message header for full name]


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