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  1. #1
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    Default Mathematical explanation for Einstein's Cross



    Does anyone understand why there are four (plus the central) images of the Quasar in Einstein's Cross instead of a doublet, arcs or a circle? If the quadruple image is caused by non-symmetrical mass distribution in the galactic "lens," then what is that distribution?

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    more than likely because of the shape of the galaxy or even maybe galaxies between it and us -
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  3. #3
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    Default RE: Mathematical explanation for Einstein's Cross

    The precise type of image obtained from a gravitational lens is indeed strongly dependent on the shape (specifically the mass distribution) of the lensing galaxy (or cluster of galaxies), as well as the alignment of the source, lensing object and observer. A full Einstein ring can only be achieved with a very compact spherical mass or one with a circularly symmetric mass distribution around the line of sight. Lenses with asymmetric mass distributions can produce smeared arcs and multiple images, including the the quadruple images seen in the Einstein Cross. Most objects producing strong lensing are massive, dense, usually elliptical galaxies or clusters of galaxies. The modeling of the mass distribution of the lens based on the observed image is thus a complicated business, but has been pretty thoroughly addressed.

    The section on gravitational lensing in this article by J. Cohn of Berkeley has many links to web sources, including methods and software for modeling lens mass distributions:
    What is Theoretical Physical Cosmology?

    Other links relevant to the different types of images formed by gravitational lenses are:
    Zooite Guide to Strong Gravitational Lenses
    and
    Possible strong gravitational lenses

    A demonstration of lensing by Peter Newberry referred to in the previous article is here:
    Gravitational Lensing Demonstration

    An example of software used for this purpose developed for the "CASTLES" project is here:
    "GRAVLENS" - Software for Gravitational Lensing

    It's been a long while since I worked on this stuff. I enjoyed the opportunity to review it and hope it helps.
    Jerry

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    rspowell7 (05-21-2011)

  5. #4
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    Well that's telling them - thanks Graypath ( or is it Col Sanders younger brother?)
    I usually have the concept but not the maths - I gave up maths at e^1-t.
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  6. #5
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    Well...not sure I have the will to follow all of the math anymore myself. Should be left to the youngsters! As for the Colonel - no relation and I don't have a white suit, but he is from Kentucky like me and I met him once in Lexington when I was a college student long ago!
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  7. #6
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    Default

    Thanks for the thoughtful reply and the references. My buddy at the gym thinks that the lens for Einstein's Cross is a spiral or eliptical galaxy almost edge on. I'll see what the references say. Thanks again.

  8. #7
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    I think there's two galaxies at right angles to each other
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  9. #8
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    Default

    Jennifer. Thanks for responding. Wow, two perpendicular galaxies? I hadn't considered that. So, from your viewpoint, the actual mass distribution of the gravitational lensing associated with Einstein's Cross is still an open question? No wonder I can't find a reference!

 

 

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  1. Why is Einstein's Cross a cross?
    By Robin Leadbeater in forum UK Astronomy Forum
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    Last Post: 11-04-2003, 10:17 AM

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