Einstein's Cross/APOD 05/03/27

Comments and questions about the APOD on the main view screen.
Axel
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Einstein's Cross/APOD 05/03/27

Post by Axel » Sun Mar 27, 2005 10:47 pm

Why is it four images rather than a ring?

Kid
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Post by Kid » Mon Mar 28, 2005 11:32 am

It was already explained in that picture
tell me if i am repeating questions

Axel
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Really?

Post by Axel » Mon Mar 28, 2005 1:34 pm

I'm sorry, I don't see the explanation. The caption says that the light bent by gravitational lensing produces four images of the distant quasar, but it does not explain why there are not eight, or sixteen, or thirty-seven images, or a uniform ring.

makc
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Post by makc » Mon Mar 28, 2005 3:29 pm

I can't find perfect explanation link, but in a few words it goes like this: you see ring when light source is directly behind the mass; if it is not so "directly" behind, you see arcs; if it is not behind "at all", you see multiple images. Try reading here.

Update: things are getting even more complex, if you 'll consider a number of masses on the light path:
http://www.cita.utoronto.ca/%7Ehoekstra/lensing.html wrote:Image
The paths of three light rays travelling through a computer simulation. The deflections have been grossly
enhanced (in the real universe the deflections are very small). All the filaments and clusters change the
paths and the shape of the galaxy we observe at Earth has been changed (it original shape can be seen at
the left side of the image). Credit: S. Colombi (IAP), CFHT Team.

Axel
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Post by Axel » Mon Mar 28, 2005 4:00 pm

Thanks for the link and the very informative diagram from the CFHT group. I took a quick look and decided it's worth mentioning Dr Kaiser's course on galaxies at Southampton:
http://www.astro.soton.ac.uk/~crk/PH227/
The webpage you referenced is one of its nodes.

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Orca
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Post by Orca » Tue Mar 29, 2005 4:58 am

BANG wrote:It was already explained in that picture
Wow...noob, aka BANG, getting snappy about an explanation...that's ironic...

makc
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Post by makc » Tue Mar 29, 2005 6:17 am

Orca wrote:...getting snappy about an explanation...that's ironic...
No, that's rather typical. People learn from other people, and that ain't necessary good things every time :(

Kid
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Post by Kid » Fri Apr 01, 2005 10:21 am

naaaaaaa. i am just stupid, thats all!
tell me if i am repeating questions