Einstein Cross vs. Ring: Understanding the Alignment of Quasar G2237+030

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    Cross Einstein Ring
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Discussion Overview

The discussion revolves around the phenomenon of gravitational lensing as exemplified by the Einstein cross (G2237+030) and the conditions under which it produces multiple images versus an Einstein ring. Participants explore the alignment of the quasar with the galactic nucleus and the implications for lensing effects.

Discussion Character

  • Exploratory, Technical explanation, Conceptual clarification

Main Points Raised

  • One participant notes that the Einstein cross shows four images of the quasar, suggesting good alignment with the galactic nucleus.
  • Another participant proposes that an Einstein ring occurs only with perfect alignment, while a nearly perfect alignment results in two images.
  • It is mentioned that if the lens is not a point but an extended ellipsoidal object, more than two images can be produced.
  • A participant shares a link to a simulation tool that allows users to visualize different lensing scenarios, including Einstein rings and crosses.
  • Another participant expresses gratitude for the information shared, indicating engagement with the discussion.

Areas of Agreement / Disagreement

Participants express varying views on the conditions necessary for the formation of an Einstein ring versus an Einstein cross, indicating that multiple competing views remain without a clear consensus.

Contextual Notes

Some assumptions about the nature of the lensing object and the alignment conditions are not fully explored, leaving room for further clarification and discussion.

Who May Find This Useful

Individuals interested in gravitational lensing, astrophysics, and the study of quasars may find this discussion relevant.

Jorrie
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The Einstein cross (G2237+030) shows 4 reasonably symmetrically spaced images of the very distant quasar, indicating that our alignment with the galactic nucleus to quasar line is fairly good.

How is that it does not show an Einstein ring instead of the cross?

Grav-lens-Einstein_Cross.jpg
 
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Jorrie said:
How is that it does not show an Einstein ring instead of the cross?

I think that a ring occurs only for perfect alignment.

A sperical point lens for which the alignment is almost (but not quite) perfect produces two images. Hartle has a nice treatment of the images shapes in this case.

If the lens is a not a point (very small) sphere, e.g., an extended ellipsoidal object, more than two images can be produced.
 
Ditto George, but I add a link to The World's Greatest GTR Simulation!http://www.iam.ubc.ca/~newbury/lenses/lenses.html
Here you can play with your heart's content, producing Einstein rings, Einstein crosses, arcs, and so on, by moving around the background object being lensed, wrt the foreground galaxy.

At the site mentioned in my sig you can find other simulations which I have some reason to think are not entirely incorrect. Caution is advised in all other cases!
 
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