Why is Einstein's Cross a cross?

Does anyone know of an explanation why the gravitationally lensed quasar in
Einsteins Cross appears as four symmetric point images instead of perhaps a
ring as one might expect if the lensing object was a point source? Does it
tell us something about the structure of the lensing galaxy? If so what?

Robin

"Robin Leadbeater" wrote in message
...
Does anyone know of an explanation why the gravitationally lensed quasar
in
Einsteins Cross appears as four symmetric point images instead of perhaps
a
ring as one might expect if the lensing object was a point source? Does
it
tell us something about the structure of the lensing galaxy? If so what?



It's OK, someone else has pointed me to the answer. I was on the right
lines. If you are interested, see

http://brahms.phy.vanderbilt.edu/cla.../gravitational
lens.html

Robin