View Full Version : Gravitational lenses

2004-Feb-13, 04:49 PM
In this recent artcle
it says that almost all known gravitational lenses have an even number of images visible, while theory predicts odd numbers. How does this lensing work exactly, and why would we expect odd numbers. And of course why do we see only even numbers?

2004-Feb-13, 08:59 PM
I found this resource:


It has a few simulations as well as examples, hope it helps

2004-Feb-13, 09:51 PM
After you read all the information at this pdf file site.... especially the Introduction. I am sure you will understand...

Hope this help


2004-Feb-13, 11:17 PM
Thanks Tiny,
This paper is way over my head, if people talk about 4 d space-time and Lorentzian Manifolds, I'm lost. It could all be very true what is said (the basic premise of this article is that there is no need for odd numbered images in lensing), but I wasn't even aware that there was a problem at all.
So maybe someone could explain where the problem started (in plain English) and then explain what the article is all about (I mean this article http://www.iam.ubc.ca/~newbury/lenses/lenses.html)


2004-Feb-14, 03:54 AM
Simple, English? Can not locate, specifics. :ph34r:

2004-Feb-14, 11:20 AM
Gravitational lensing? Occurs when light travels in a gravitational field. Typically only noticable in strong gravitational fields (ie. sun, black hole). It was originally predicted with the General Theory of Relativity. It occurs when light is bent toward the body of mass because of gravitation. It makes stars appear to be in different positions than they should be. Or in a black holes' case the light is focused, or a whole group of stars may look like 1 really bright star.

Hope this helps.

2004-Feb-14, 07:57 PM
Thanks, Matthew,
Ad you say, the principle of gravitational lensing is the bending of light by strong gravity fields much like an optical lens. The problem stated in the article is that an odd number of images are expected from a distant source (quasar) when it is lensed by a closer galaxy. What is found is almost always an even number of images. Whys are these odd numbers expected and why do we see even numbers?
Before this article I never heard of this problem and for a long time it was believed (wasn't Zwicky the guy who searched for lenses?) that gravitational lensing was too rare to observe. Only in the last decades many "lenses" and images have been found.

2004-Feb-15, 04:59 AM
Lensing, gravitaional, quasar. Recent funding for tech. :ph34r: I suppose all the support HAS helped. Rollin, rollin, rollin...diggin, diggin, diggen..Rawhide :P

2004-Feb-15, 05:17 AM
Only in the last decades many "lenses" and images have been found. That stands to reason, as our understanding and techniques have improved.

Just as Victoria said, i think - we keep on diggin'

2004-Feb-15, 11:07 AM
Yes, Damien, that answers my second question (as did Victoria although I needed your "explanation" to understand what she meant; yes i'm quite dense), but the first question is still unanswered; why does theory predict odd numbers of images and why do we see even numbers. Is there a problem with the theory or is there a problem with the observations?

2004-Feb-16, 05:03 PM
I saw this Hubble image
and it shows a very deep field image of galaxies, apparently some of them are lensed (and at the edge of the Universe). The strange streaks and all kinds of funny features that are visible, are they also caused by lensing, or are these semi-circular "galaxies" actually the way we see them?
Some of these features are in front of normal shaped galaxies, does that mean that they can't be the result of lensing?